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<rfc ipr="trust200902" docName="draft-ietf-spring-srv6-srh-compression-23" categ <rfc xmlns:xi="http://www.w3.org/2001/XInclude" ipr="trust200902" docName="draft
ory="std" consensus="true" submissionType="IETF" updates="8754" tocInclude="true -ietf-spring-srv6-srh-compression-23" number="9800" category="std" consensus="tr
" sortRefs="true" symRefs="true"> ue" submissionType="IETF" updates="8754" obsoletes="" tocInclude="true" sortRefs
<front> ="true" symRefs="true" version="3" xml:lang="en">
<title abbrev="Compressed SRv6 Segment List Encoding">Compressed SRv6 Segmen
t List Encoding (CSID)</title>
<front>
<title abbrev="Compressed SRv6 Segment List Encoding">Compressed
SRv6 Segment List Encoding (CSID)</title>
<seriesInfo name="RFC" value="9800"/>
<author initials="W." surname="Cheng" fullname="Weiqiang Cheng" role="editor "> <author initials="W." surname="Cheng" fullname="Weiqiang Cheng" role="editor ">
<organization>China Mobile</organization> <organization>China Mobile</organization>
<address> <address>
<postal> <postal>
<country>China</country> <country>China</country>
</postal> </postal>
<email>chengweiqiang@chinamobile.com</email> <email>chengweiqiang@chinamobile.com</email>
</address> </address>
</author> </author>
<author initials="C." surname="Filsfils" fullname="Clarence Filsfils"> <author initials="C." surname="Filsfils" fullname="Clarence Filsfils">
skipping to change at line 80 skipping to change at line 68
</author> </author>
<author initials="F." surname="Clad" fullname="Francois Clad" role="editor"> <author initials="F." surname="Clad" fullname="Francois Clad" role="editor">
<organization>Cisco Systems, Inc.</organization> <organization>Cisco Systems, Inc.</organization>
<address> <address>
<postal> <postal>
<country>France</country> <country>France</country>
</postal> </postal>
<email>fclad.ietf@gmail.com</email> <email>fclad.ietf@gmail.com</email>
</address> </address>
</author> </author>
<date year="2025" month="June"/>
<date year="2025" month="February" day="06"/> <area>RTG</area>
<workgroup>spring</workgroup>
<area>General</area>
<workgroup>SPRING</workgroup>
<keyword>Internet-Draft</keyword>
<abstract>
<?line 244?>
<t>Segment Routing over IPv6 (SRv6) is the instantiation of Segment Routing (SR) <!-- [rfced] Please insert any keywords (beyond those that appear in
on the IPv6 dataplane. This document specifies new flavors for the SRv6 endpoin the title) for use on https://www.rfc-editor.org/search. -->
t behaviors defined in RFC 8986, which enable the compression of an SRv6 segment
list. Such compression significantly reduces the size of the SRv6 encapsulation
needed to steer packets over long segment lists.</t>
<t>This document updates RFC 8754 by allowing a Segment List entry in the Segmen t Routing Header (SRH) to be either an IPv6 address, as specified in RFC 8754, o r a REPLACE-CSID container in packed format, as specified in this document.</t> <keyword>example</keyword>
<abstract>
<t>Segment Routing over IPv6 (SRv6) is the instantiation of Segment Routing (SR)
on the IPv6 data plane. This document specifies new flavors for the SRv6 endpoi
nt behaviors defined in RFC 8986, which enable the compression of an SRv6 segmen
t list. Such compression significantly reduces the size of the SRv6 encapsulatio
n needed to steer packets over long segment lists.</t>
<t>This document updates RFC 8754 by allowing a Segment List entry in the
Segment Routing Header (SRH) to be either an IPv6 address, as specified in RFC 8
754, or a REPLACE-CSID container in packed format, as specified in this document
.</t>
</abstract> </abstract>
</front> </front>
<middle> <middle>
<?line 250?>
<?line 250?> <section anchor="introduction">
<name>Introduction</name>
<section anchor="introduction"><name>Introduction</name> <t>The Segment Routing (SR) architecture <xref target="RFC8402"/> describe
s two data plane instantiations of SR: SR over MPLS (SR-MPLS) and SR over IPv6 (
<t>The Segment Routing (SR) architecture <xref target="RFC8402"/> describes two SRv6).</t>
data plane instantiations of SR: SR over MPLS (SR-MPLS) and SR over IPv6 (SRv6). <t>SRv6 Network Programming <xref target="RFC8986"/> builds upon the IPv6
</t> Segment Routing Header (SRH) <xref target="RFC8754"/> to define a framework for
constructing a network program with topological and service segments.</t>
<t>SRv6 Network Programming <xref target="RFC8986"/> builds upon the IPv6 Segmen <t>Some SRv6 applications, such as strict path traffic engineering, may re
t Routing Header (SRH) <xref target="RFC8754"/> to define a framework for constr quire long segment lists. Compressing the encoding of these long segment lists i
ucting a network program with topological and service segments.</t> n the packet header can significantly reduce the header size. This document spec
ifies new flavors to the SRv6 endpoint behaviors defined in <xref target="RFC898
<t>Some SRv6 applications such as strict path traffic engineering may require lo 6"/> that enable a compressed encoding of the SRv6 segment list.
ng segment lists. Compressing the encoding of these long segment lists in the pa
cket header can significantly reduce the header size. This document specifies ne
w flavors to the SRv6 endpoint behaviors defined in <xref target="RFC8986"/> tha
t enable a compressed encoding of the SRv6 segment list.
This document also specifies new SRv6 endpoint behaviors to preserve the compres sion efficiency in multi-domain environments.</t> This document also specifies new SRv6 endpoint behaviors to preserve the compres sion efficiency in multi-domain environments.</t>
<t>The SRv6 endpoint behaviors defined in this document leverage the SRv6
data plane defined in <xref target="RFC8754"/> and <xref target="RFC8986"/>; the
behaviors are compatible with the SRv6 control plane extensions for IS-IS <xref
target="RFC9352"/>, OSPF <xref target="RFC9513"/>, and BGP <xref target="RFC925
2"/>.</t>
<t>This document updates <xref target="RFC8754"/> by allowing a Segment Li
st entry in the SRH to be either an IPv6 address, as specified in <xref target="
RFC8754"/>, or a REPLACE-CSID container in packed format, as specified in <xref
target="sec-replace"/>.</t>
</section>
<section anchor="terminology">
<name>Terminology</name>
<t>This document leverages the terms defined in <xref target="RFC8402"/>,
<xref target="RFC8754"/>, and <xref target="RFC8986"/>, in particular segment, s
egment list, Segment Identifier (SID), SID list, SR policy, prefix segment, adja
cency segment, SRH, SR domain, SR source node, SR segment endpoint node, transit
node, SRv6 endpoint behavior, flavor, SID block, locator, function, and argumen
t. The reader is assumed to be familiar with this terminology.</t>
<t>This document introduces the following new terms:</t>
<t>The SRv6 endpoint behaviors defined in this document leverage the SRv6 data p <dl spacing="normal" newline="false">
lane defined in <xref target="RFC8754"/> and <xref target="RFC8986"/>, and are c <dt>Locator-Block:</dt><dd>The most significant bits of a SID locator
ompatible with the SRv6 control plane extensions for IS-IS <xref target="RFC9352 that represent the SRv6 SID block. The Locator-Block is referred to as
"/>, OSPF <xref target="RFC9513"/>, and BGP <xref target="RFC9252"/>.</t> "B" in <xref target="RFC8986" sectionFormat="of" section="3.1"/>.</dd>
<dt>Locator-Node:</dt><dd>The least significant bits of a SID locator
<t>This document updates <xref target="RFC8754"/> by allowing a Segment List ent that identify the SR segment endpoint node instantiating the SID. The
ry in the SRH to be either an IPv6 address, as specified in <xref target="RFC875 Locator-Node is referred to as "N" in <xref
4"/>, or a REPLACE-CSID container in packed format, as specified in <xref target target="RFC8986" sectionFormat="of" section="3.1"/>.</dd>
="sec-replace"/>.</t> <dt>Compressed-SID (CSID):</dt><dd>A compressed encoding of a SID. The
CSID includes the Locator-Node and Function bits of the SID being
</section> compressed. If either constituent of the SID is empty (zero length),
<section anchor="terminology"><name>Terminology</name> then the same applies to its CSID encoding.</dd>
<dt>CSID container:</dt><dd>A 128-bit IPv6 address that functions as a
<t>This document leverages the terms defined in <xref target="RFC8402"/>, <xref container holding a list of one or more CSIDs and the Argument (if
target="RFC8754"/>, and <xref target="RFC8986"/>, in particular segment, segment any) of the last CSID.</dd>
list, Segment Identifier (SID), SID list, SR policy, prefix segment, adjacency <dt>CSID sequence:</dt><dd>A group of one or more consecutive SID list
segment, SRH, SR domain, SR source node, SR segment endpoint node, transit node, entries encoding the common Locator-Block and at least one CSID
SRv6 endpoint behavior, flavor, SID block, locator, function, and argument. The container.</dd>
reader is assumed to be familiar with this terminology.</t> <dt>Compressed SID list:</dt><dd>A segment list encoding that reduces
the packet header length thanks to one or more CSID sequences. A
<t>This document introduces the following new terms:</t> compressed SID list also contains zero, one, or more uncompressed
SIDs.</dd>
<t><list style="symbols"> <dt>Global Identifiers Block (GIB):</dt><dd>The pool of CSID values
<t>Locator-Block: The most significant bits of a SID locator that represent th available for global allocation.</dd>
e SRv6 SID block. The Locator-Block is referred to as &quot;B&quot; in Section 3 <dt>Local Identifiers Block (LIB):</dt><dd>The pool of CSID values
.1 of <xref target="RFC8986"/>.</t> available for local allocation.</dd>
<t>Locator-Node: The least significant bits of a SID locator that identify the </dl>
SR segment endpoint node instantiating the SID. The Locator-Node is referred to
as &quot;N&quot; in Section 3.1 of <xref target="RFC8986"/>.</t>
<t>Compressed-SID (CSID): A compressed encoding of a SID. The CSID includes th
e Locator-Node and Function bits of the SID being compressed. If either constitu
ent of the SID is empty (zero length), then the same applies to its CSID encodin
g.</t>
<t>CSID container: A 128-bit IPv6 address that functions as a container holdin
g a list of one or more CSIDs, and the Argument (if any) of the last CSID.</t>
<t>CSID sequence: A group of one or more consecutive SID list entries encoding
the common Locator-Block and at least one CSID container.</t>
<t>Compressed SID list: A segment list encoding that reduces the packet header
length thanks to one or more CSID sequences. A compressed SID list also contain
s zero, one, or more uncompressed SIDs.</t>
<t>Global Identifiers Block (GIB): The pool of CSID values available for globa
l allocation.</t>
<t>Local Identifiers Block (LIB): The pool of CSID values available for local
allocation.</t>
</list></t>
<t>In this document, the length of each constituent part of a SID is referred to
as follows.</t>
<t><list style="symbols">
<t>LBL is the Locator-Block length of the SID.</t>
<t>LNL is the Locator-Node length of the SID.</t>
<t>FL is the Function length of the SID.</t>
<t>AL is the Argument length of the SID.</t>
</list></t>
<t>In addition, the Locator-Node and Function length (LNFL) is the sum of the Lo
cator-Node length and the Function length of the SID. It is also referred to as
the CSID length.</t>
<section anchor="requirements-language"><name>Requirements Language</name>
<t>The key words &quot;MUST&quot;, &quot;MUST NOT&quot;, &quot;REQUIRED&quot;, &
quot;SHALL&quot;, &quot;SHALL NOT&quot;, &quot;SHOULD&quot;, &quot;SHOULD NOT&qu
ot;, &quot;RECOMMENDED&quot;, &quot;NOT RECOMMENDED&quot;, &quot;MAY&quot;, and
&quot;OPTIONAL&quot; in this document are to be interpreted as described in BCP
14 <xref target="RFC2119"/> <xref target="RFC8174"/> when, and only when, they a
ppear in all capitals, as shown here.</t>
</section>
</section>
<section anchor="basic-concepts"><name>Basic Concepts</name>
<t>In an SR domain, all SRv6 SIDs instantiated from the same Locator-Block share <t>In this document, the length of each constituent part of a SID is refer
the same most significant bits. In addition, when the combined length of the SR red to as follows:</t>
v6 SID Locator, Function, and Argument is smaller than 128 bits, the least signi <ul spacing="normal">
ficant bits of the SID are padded with zeros. <li>
<t>LBL is the Locator-Block length of the SID.</t>
</li>
<li>
<t>LNL is the Locator-Node length of the SID.</t>
</li>
<li>
<t>FL is the Function length of the SID.</t>
</li>
<li>
<t>AL is the Argument length of the SID.</t>
</li>
</ul>
<t>In addition, the Locator-Node and Function length (LNFL) is the sum of
the Locator-Node length and the Function length of the SID. It is also referred
to as the "CSID length".</t>
<section anchor="requirements-language">
<name>Requirements Language</name>
<t>
The key words "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>", "<bcp14>REQU
IRED</bcp14>", "<bcp14>SHALL</bcp14>", "<bcp14>SHALL
NOT</bcp14>", "<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NOT</bcp14>", "<bcp14>
RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>",
"<bcp14>MAY</bcp14>", and "<bcp14>OPTIONAL</bcp14>" in this document are to
be interpreted as
described in BCP&nbsp;14 <xref target="RFC2119"/> <xref target="RFC8174"/>
when, and only when, they appear in all capitals, as shown here.
</t>
</section>
</section>
<section anchor="basic-concepts">
<name>Basic Concepts</name>
<t>In an SR domain, all SRv6 SIDs instantiated from the same Locator-Block
share the same most significant bits. In addition, when the combined length of
the SRv6 SID Locator, Function, and Argument is smaller than 128 bits, the least
significant bits of the SID are padded with zeros.
The compressed segment list encoding seeks to decrease the packet header length by avoiding the repetition of the same Locator-Block and reducing the use of pad ding bits.</t> The compressed segment list encoding seeks to decrease the packet header length by avoiding the repetition of the same Locator-Block and reducing the use of pad ding bits.</t>
<t>Building upon, and fully compatible with, the mechanisms specified in <
<t>Building upon and fully compatible with the mechanisms specified in <xref tar xref target="RFC8754"/> and <xref target="RFC8986"/>, the compressed segment lis
get="RFC8754"/> and <xref target="RFC8986"/>, the compressed segment list encodi t encoding leverages a SID list compression logic at the SR source node (see <xr
ng leverages a SID list compression logic at the SR source node (see <xref targe ef target="sec-source-node"/>) in combination with new flavors of the SRv6 endpo
t="sec-source-node"/>) in combination with new flavors of the SRv6 endpoint beha int behaviors that process the compressed SID list (see <xref target="sec-endpoi
viors that process the compressed SID list (see <xref target="sec-endpoint"/>).< nt"/>).</t>
/t> <t>An SR source node constructs and compresses the SID list depending on t
he SIDs instantiated on each SR segment endpoint node that the packet is intende
<t>An SR source node constructs and compresses the SID list depending on the SID d to traverse, as well as its own compression capabilities. The resulting compre
s instantiated on each SR segment endpoint node that the packet is intended to t ssed SID list is a combination of CSID sequences, for the SIDs that the SR sourc
raverse, as well as its own compression capabilities. The resulting compressed S e node was able to compress, and uncompressed SIDs, which could not be compresse
ID list is a combination of CSID sequences, for the SIDs that the SR source node d. In case the SR source node is able to compress all the SIDs in the SID list,
was able to compress, and uncompressed SIDs, which could not be compressed. In the compressed SID list comprises only CSID sequences (one or more) and no uncom
case the SR source node is able to compress all the SIDs in the SID list, the co pressed SIDs. Conversely, the compressed SID list comprises only uncompressed SI
mpressed SID list comprises only CSID sequences (one or more), and no uncompress Ds when the SR source is unable to compress any of the constituent SIDs.</t>
ed SIDs. Conversely, the compressed SID list comprises only uncompressed SIDs wh </section>
en the SR source is unable to compress any of the constituent SIDs.</t> <section anchor="sec-endpoint">
<name>SR Segment Endpoint Flavors</name>
</section> <t>This section defines two SR segment endpoint flavors: NEXT-CSID and REP
<section anchor="sec-endpoint"><name>SR Segment Endpoint Flavors</name> LACE-CSID, for the End, End.X, End.T, End.B6.Encaps, End.B6.Encaps.Red, and End.
BM behaviors of <xref target="RFC8986"/>.</t>
<t>This section defines two SR segment endpoint flavors, NEXT-CSID and REPLACE-C <t>This section also defines a REPLACE-CSID flavor for the End.DX6, End.DX
SID, for the End, End.X, End.T, End.B6.Encaps, End.B6.Encaps.Red, and End.BM beh 4, End.DT6, End.DT4, End.DT46, End.DX2, End.DX2V, End.DT2U, and End.DT2M behavio
aviors of <xref target="RFC8986"/>.</t> rs of <xref target="RFC8986"/>.
A counterpart NEXT-CSID flavor is not defined for these behaviors. Any SID can b
<t>This section also defines a REPLACE-CSID flavor for the End.DX6, End.DX4, End e the last element of a CSID sequence compressed using the NEXT-CSID flavor (see
.DT6, End.DT4, End.DT46, End.DX2, End.DX2V, End.DT2U, and End.DT2M behaviors of <xref target="sec-next"/>) and the aforementioned SRv6 endpoint behaviors are a
<xref target="RFC8986"/>. lways in the last position in a SID list; thus, there is no need for any modific
A counterpart NEXT-CSID flavor is not defined for these behaviors: since any SID ation of the behaviors defined in <xref target="RFC8986"/>.</t>
can be the last element of a CSID sequence compressed using the NEXT-CSID flavo <t>Future documents may extend the applicability of the NEXT-CSID and REPL
r (see <xref target="sec-next"/>) and the aforementioned SRv6 endpoint behaviors ACE-CSID flavors to other SRv6 endpoint behaviors (see <xref target="sec-future"
are always in the last position in a SID list, there is no need for any modific />).</t>
ation of the behaviors defined in <xref target="RFC8986"/>.</t> <t>The use of these flavors, either individually or in combination, enable
s the compressed segment list encoding.</t>
<t>Future documents may extend the applicability of the NEXT-CSID and REPLACE-CS <t>The NEXT-CSID flavor and the REPLACE-CSID flavor both leverage the SID
ID flavors to other SRv6 endpoint behaviors (see <xref target="sec-future"/>).</ Argument to determine the next SID to be processed, but employ different SID lis
t> t compression schemes.
With the NEXT-CSID flavor, each CSID container is a fully formed SRv6 SID with t
<t>The use of these flavors, either individually or in combination, enables the he common Locator-Block for all the CSIDs in the CSID container, a Locator-Node,
compressed segment list encoding.</t> and Function that are those of the first CSID, and an Argument carrying the sub
sequent CSIDs.
<t>The NEXT-CSID flavor and the REPLACE-CSID flavor both leverage the SID Argume
nt to determine the next SID to be processed, but employ different SID list comp
ression schemes.
With the NEXT-CSID flavor, each CSID container is a fully formed SRv6 SID with t
he common Locator-Block for all the CSIDs in the CSID container, a Locator-Node
and Function that are those of the first CSID, and an Argument carrying the subs
equent CSIDs.
With the REPLACE-CSID flavor, only the first element in a CSID sequence is a ful ly formed SRv6 SID. It has the common Locator-Block for all the CSIDs in the CSI D sequence, and a Locator-Node and Function that are those of the first CSID. Th e remaining elements in the CSID sequence are CSID containers carrying the subse quent CSIDs without the Locator-Block.</t> With the REPLACE-CSID flavor, only the first element in a CSID sequence is a ful ly formed SRv6 SID. It has the common Locator-Block for all the CSIDs in the CSI D sequence, and a Locator-Node and Function that are those of the first CSID. Th e remaining elements in the CSID sequence are CSID containers carrying the subse quent CSIDs without the Locator-Block.</t>
<t>Regardless of which flavor is used, the IPv6 address carried in the Des
<t>Regardless of which flavor is used, the IPv6 address carried in the Destinati tination Address field of the IPv6 header is a valid SRv6 SID conforming to <xre
on Address field of the IPv6 header is a valid SRv6 SID conforming to <xref targ f target="RFC9602"/>.</t>
et="RFC9602"/>.</t> <t>In the remainder of this document, the term "a SID of this document" re
fers to any End, End.X, End.T, End.B6.Encaps, End.B6.Encaps.Red, or End.BM SID w
<t>In the remainder of this document, the term &quot;a SID of this document&quot ith the NEXT-CSID or the REPLACE-CSID flavor and with any combination of Penulti
; refers to any End, End.X, End.T, End.B6.Encaps, End.B6.Encaps.Red, or End.BM S mate Segment Pop (PSP), Ultimate Segment Pop (USP), and Ultimate Segment Decapsu
ID with the NEXT-CSID or the REPLACE-CSID flavor, and with any combination of Pe lation (USD) flavor, or any End.DX6, End.DX4, End.DT6, End.DT4, End.DT46, End.DX
nultimate Segment Pop (PSP), Ultimate Segment Pop (USP), and Ultimate Segment De 2, End.DX2V, End.DT2U, or End.DT2M with the REPLACE-CSID flavor. All the SRv6 en
capsulation (USD) flavor, or any End.DX6, End.DX4, End.DT6, End.DT4, End.DT46, E dpoint behaviors introduced in this document are listed in <xref target="tbl-ian
nd.DX2, End.DX2V, End.DT2U, or End.DT2M with the REPLACE-CSID flavor. All the SR a-endpoint-behaviors"/>.</t>
v6 endpoint behaviors introduced in this document are listed in <xref target="tb <t>In the remainder of this document, the terms "NEXT-CSID flavor SID" and
l-iana-endpoint-behaviors"/> at the end of the document.</t> "REPLACE-CSID flavor SID" refer to any SID of this document with the NEXT-CSID
flavor and with the REPLACE-CSID flavor, respectively.</t>
<t>In the remainder of this document, the terms &quot;NEXT-CSID flavor SID&quot; <section anchor="sec-next">
and &quot;REPLACE-CSID flavor SID&quot; refer to any SID of this document with <name>NEXT-CSID Flavor</name>
the NEXT-CSID flavor and with the REPLACE-CSID flavor, respectively.</t> <t>A CSID sequence compressed using the mechanism of the NEXT-CSID flavo
r comprises one or more CSID containers. Each CSID container is a fully formed 1
<section anchor="sec-next"><name>NEXT-CSID Flavor</name> 28-bit SID structured as shown in <xref target="fig-next-struct"/>. It carries a
Locator-Block followed by a series of CSIDs. The Locator-Node and Function of t
<t>A CSID sequence compressed using the mechanism of the NEXT-CSID flavor compri he CSID container are those of the first CSID, and its Argument is the contiguou
ses one or more CSID containers. Each CSID container is a fully formed 128-bit S s series of subsequent CSIDs. The second CSID is encoded in the most significant
ID structured as shown in <xref target="fig-next-struct"/>. It carries a Locator bits of the CSID container Argument. The third CSID is encoded in the bits of
-Block followed by a series of CSIDs. The Locator-Node and Function of the CSID the Argument that immediately follow the second CSID, and so on. When all CSIDs
container are those of the first CSID, and its Argument is the contiguous series have the same length, a CSID container can carry up to K CSIDs, where K is compu
of subsequent CSIDs. The second CSID is encoded in the most significant bits of ted as floor((128-LBL)/LNFL) (floor(x) is the greatest integer less than or equa
the CSID container Argument, the third CSID is encoded in the bits of the Argum l to x <xref target="GKP94"/>). Each CSID container for NEXT-CSID is independent
ent that immediately follow the second CSID, and so on. When all CSIDs have the , such that contiguous CSID containers in a CSID sequence can be considered to b
same length, a CSID container can carry up to K CSIDs, where K is computed as fl e separate CSID sequences.</t>
oor((128-LBL)/LNFL) (floor(x) is the greatest integer less than or equal to x <x <t>When a CSID sequence compressed using the NEXT-CSID flavor comprises
ref target="GKP94"/>). Each CSID container for NEXT-CSID is independent, such th at least two CSIDs, the last CSID in the sequence is not required to have the NE
at contiguous CSID containers in a CSID sequence can be considered as separate C XT-CSID flavor. It can be bound to any SRv6 endpoint behavior, including <xref t
SID sequences.</t> arget="RFC8986"/> behaviors and REPLACE-CSID flavor, as long as the updated dest
ination address resulting from the processing of the previous CSID in the sequen
<t>When a CSID sequence compressed using the NEXT-CSID flavor comprises at least ce is a valid form for that last SID. Line S12 of the first pseudocode in <xref
two CSIDs, the last CSID in the sequence is not required to have the NEXT-CSID target="sec-source-compression"/> provides sufficient conditions to ensure this
flavor. It can be bound to any SRv6 endpoint behavior, including <xref target="R property.</t>
FC8986"/> behaviors and REPLACE-CSID flavor, as long as the updated destination <figure anchor="fig-next-struct">
address resulting from the processing of the previous CSID in the sequence is a <name>Structure of a NEXT-CSID Flavor SID (Scaled for a 48-Bit Locator
valid form for that last SID. Line S12 of the first pseudocode in <xref target=" -Block, 16-Bit Combined Locator-Node and Function, and 64-Bit Argument)</name>
sec-source-compression"/> provides sufficient conditions to ensure this property <artset>
.</t> <artwork type="svg"><svg xmlns="http://www.w3.org/2000/svg" version=
"1.1" height="128" width="552" viewBox="0 0 552 128" class="diagram" text-anchor
<figure title="Structure of a NEXT-CSID flavor SID (scaled for a 48-bit Locator- ="middle" font-family="monospace" font-size="13px" stroke-linecap="round">
Block, 16-bit combined Locator-Node and Function, and 64-bit Argument)" anchor=" <path d="M 8,32 L 8,80" fill="none" stroke="black"/>
fig-next-struct"><artset><artwork type="svg"><svg xmlns="http://www.w3.org/2000 <path d="M 208,40 L 208,72" fill="none" stroke="black"/>
/svg" version="1.1" height="128" width="552" viewBox="0 0 552 128" class="diagra <path d="M 280,40 L 280,72" fill="none" stroke="black"/>
m" text-anchor="middle" font-family="monospace" font-size="13px" stroke-linecap= <path d="M 544,32 L 544,80" fill="none" stroke="black"/>
"round"> <path d="M 8,32 L 544,32" fill="none" stroke="black"/>
<path d="M 8,32 L 8,80" fill="none" stroke="black"/> <path d="M 8,80 L 544,80" fill="none" stroke="black"/>
<path d="M 208,40 L 208,72" fill="none" stroke="black"/> <path d="M 16,96 L 200,96" fill="none" stroke="black"/>
<path d="M 280,40 L 280,72" fill="none" stroke="black"/> <path d="M 216,96 L 272,96" fill="none" stroke="black"/>
<path d="M 544,32 L 544,80" fill="none" stroke="black"/> <path d="M 288,96 L 536,96" fill="none" stroke="black"/>
<path d="M 8,32 L 544,32" fill="none" stroke="black"/> <polygon class="arrowhead" points="544,96 532,90.4 532,101.6" fi
<path d="M 8,80 L 544,80" fill="none" stroke="black"/> ll="black" transform="rotate(0,536,96)"/>
<path d="M 16,96 L 200,96" fill="none" stroke="black"/> <polygon class="arrowhead" points="296,96 284,90.4 284,101.6" fi
<path d="M 216,96 L 272,96" fill="none" stroke="black"/> ll="black" transform="rotate(180,288,96)"/>
<path d="M 288,96 L 536,96" fill="none" stroke="black"/> <polygon class="arrowhead" points="280,96 268,90.4 268,101.6" fi
<polygon class="arrowhead" points="544,96 532,90.4 532,101.6" fill="black" trans ll="black" transform="rotate(0,272,96)"/>
form="rotate(0,536,96)"/> <polygon class="arrowhead" points="224,96 212,90.4 212,101.6" fi
<polygon class="arrowhead" points="296,96 284,90.4 284,101.6" fill="black" trans ll="black" transform="rotate(180,216,96)"/>
form="rotate(180,288,96)"/> <polygon class="arrowhead" points="208,96 196,90.4 196,101.6" fi
<polygon class="arrowhead" points="280,96 268,90.4 268,101.6" fill="black" trans ll="black" transform="rotate(0,200,96)"/>
form="rotate(0,272,96)"/> <polygon class="arrowhead" points="24,96 12,90.4 12,101.6" fill=
<polygon class="arrowhead" points="224,96 212,90.4 212,101.6" fill="black" trans "black" transform="rotate(180,16,96)"/>
form="rotate(180,216,96)"/> <g class="text">
<polygon class="arrowhead" points="208,96 196,90.4 196,101.6" fill="black" trans <text x="104" y="52">Locator-Block</text>
form="rotate(0,200,96)"/> <text x="244" y="52">Loc-Node</text>
<polygon class="arrowhead" points="24,96 12,90.4 12,101.6" fill="black" transfor <text x="412" y="52">Argument</text>
m="rotate(180,16,96)"/> <text x="244" y="68">Function</text>
<g class="text"> <text x="104" y="116">LBL</text>
<text x="104" y="52">Locator-Block</text> <text x="244" y="116">LNFL</text>
<text x="244" y="52">Loc-Node</text> <text x="412" y="116">AL</text>
<text x="412" y="52">Argument</text> </g>
<text x="244" y="68">Function</text> </svg>
<text x="104" y="116">LBL</text> </artwork>
<text x="244" y="116">LNFL</text> <artwork type="ascii-art"><![CDATA[
<text x="412" y="116">AL</text>
</g>
</svg>
</artwork><artwork type="ascii-art"><![CDATA[
+------------------------------------------------------------------+ +------------------------------------------------------------------+
| Locator-Block |Loc-Node| Argument | | Locator-Block |Loc-Node| Argument |
| |Function| | | |Function| |
+------------------------------------------------------------------+ +------------------------------------------------------------------+
<----------------------> <------> <------------------------------> <----------------------> <------> <------------------------------>
LBL LNFL AL LBL LNFL AL
]]></artwork></artset></figure> ]]></artwork>
</artset>
<t><xref target="fig-next-csid-list"/> illustrates a compressed SID list as coul </figure>
d be produced by an SR source node steering a packet into an SR policy with a SI <t><xref target="fig-next-csid-list"/> illustrates a compressed SID list
D list of eight NEXT-CSID flavor SIDs. All SIDs in this example have a 48-bit Lo as could be produced by an SR source node steering a packet into an SR policy w
cator-Block, 16-bit combined Locator-Node and Function, and 64-bit Argument. The ith a SID list of eight NEXT-CSID flavor SIDs. All SIDs in this example have a 4
SR source node compresses the SR policy SID list as a compressed SID list of tw 8-bit Locator-Block, 16-bit combined Locator-Node and Function, and 64-bit Argum
o CSID containers. The first CSID container carries a Locator-Block and the firs ent. The SR source node compresses the SR policy SID list as a compressed SID li
t five CSIDs. The second CSID container carries a Locator-Block and the sixth, s st of two CSID containers. The first CSID container carries a Locator-Block and
eventh, and eighth CSIDs. Since the SR source node does not use the second CSID the first five CSIDs. The second CSID container carries a Locator-Block and the
container at full capacity, it sets the 32 least significant bits to zero. The S sixth, seventh, and eighth CSIDs. Since the SR source node does not use the seco
R source node sets the IPv6 Destination Address (DA) with the value of the first nd CSID container at full capacity, it sets the 32 least significant bits to zer
CSID container and the first element of the SRH Segment List with the value of o. The SR source node sets the IPv6 Destination Address (DA) with the value of t
the second CSID container. Without reduced SRH (Section 4.1.1 of <xref target="R he first CSID container and the first element of the SRH Segment List with the v
FC8754"/>), the SR source node also writes the first CSID container as the secon alue of the second CSID container. Without reduced SRH (see <xref target="RFC875
d element of the SRH Segment List.</t> 4" sectionFormat="of" section="4.1.1"/>), the SR source node also writes the fir
st CSID container as the second element of the SRH Segment List.</t>
<t>Note that the CSIDs within a given CSID container appear in forward order to <t>Note that the CSIDs within a given CSID container appear in forward o
leverage the longest-prefix match IP forwarding, while the entries in the SRH Se rder to leverage the longest-prefix match IP forwarding, while the entries in th
gment List appear in reversed order of their processing, as specified in Section e SRH Segment List appear in reversed order of their processing, as specified in
4.1 of <xref target="RFC8754"/>.</t> <xref target="RFC8754" sectionFormat="of" section="4.1"/>.</t>
<figure anchor="fig-next-csid-list">
<figure title="Compressed SID list of eight NEXT-CSID flavor SIDs with a 48-bit <name>Compressed SID List of Eight NEXT-CSID Flavor SIDs with a 48-Bit
Locator-Block, 16-bit combined Locator-Node and Function, and 64-bit Argument" a Locator-Block, 16-Bit Combined Locator-Node and Function, and 64-Bit Argument</
nchor="fig-next-csid-list"><artset><artwork type="svg"><svg xmlns="http://www.w name>
3.org/2000/svg" version="1.1" height="432" width="528" viewBox="0 0 528 432" cla <artset>
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<artwork type="ascii-art"><![CDATA[
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+ Locator-Block +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + Locator-Block +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | 1st CSID | | | 1st CSID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2nd CSID | 3rd CSID | | 2nd CSID | 3rd CSID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 4th CSID | 5th CSID | | 4th CSID | 5th CSID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
First CSID container First CSID Container
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+ Locator-Block +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + Locator-Block +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | 6th CSID | | | 6th CSID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 7th CSID | 8th CSID | | 7th CSID | 8th CSID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 | | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Second CSID container Second CSID Container
]]></artwork></artset></figure> ]]></artwork>
</artset>
<t>An implementation MUST support a 32-bit Locator-Block length (LBL) and a 16-b </figure>
it CSID length (LNFL) for NEXT-CSID flavor SIDs, and MAY support any additional <t>An implementation <bcp14>MUST</bcp14> support a 32-bit Locator-Block
Locator-Block and CSID length.</t> length (LBL) and a 16-bit CSID length (LNFL) for NEXT-CSID flavor SIDs, and it <
bcp14>MAY</bcp14> support any additional Locator-Block and CSID length.</t>
<t>The Argument length (AL) for NEXT-CSID flavor SIDs is equal to 128-LBL-LNFL.< <t>The Argument length (AL) for NEXT-CSID flavor SIDs is equal to 128-LB
/t> L-LNFL.</t>
<t>When processing an IPv6 packet that matches a Forwarding Information
<t>When processing an IPv6 packet that matches a Forwarding Information Base (FI Base (FIB) entry locally instantiated as a SID with the NEXT-CSID flavor, the SR
B) entry locally instantiated as a SID with the NEXT-CSID flavor, the SR segment segment endpoint node applies the procedure specified in the following subsecti
endpoint node applies the procedure specified in the following subsection that on that corresponds to the SID behavior. If the SID also has the PSP, USP, or US
corresponds to the SID behavior. If the SID also has the PSP, USP, or USD flavor D flavor, the procedure is modified as described in <xref target="sec-next-flavo
, the procedure is modified as described in <xref target="sec-next-flavors"/>.</ rs"/>.</t>
t> <t>An SR segment endpoint node instantiating a SID of this document with
the NEXT-CSID flavor <bcp14>MUST</bcp14> accept any Argument value for that SID
<t>An SR segment endpoint node instantiating a SID of this document with the NEX .</t>
T-CSID flavor MUST accept any Argument value for that SID.</t> <t>At a high level, for any SID with the NEXT-CSID flavor, the SR segmen
t endpoint node determines the next SID of the SID list as follows. If the Argum
<t>At a high level, for any SID with the NEXT-CSID flavor, the SR segment endpoi ent value of the active SID is non-zero, the SR segment endpoint node constructs
nt node determines the next SID of the SID list as follows. If the Argument valu the next SID from the active SID by copying the entire SID Argument value to th
e of the active SID is non-zero, the SR segment endpoint node constructs the nex e bits that immediately follow the Locator-Block, thus overwriting the active SI
t SID from the active SID by copying the entire SID Argument value to the bits t D Locator-Node and Function with those of the next CSID, and filling the least s
hat immediately follow the Locator-Block, thus overwriting the active SID Locato ignificant LNFL bits of the Argument with zeros. Otherwise (if the Argument valu
r-Node and Function with those of the next CSID, and filling the least significa e is 0), the SR segment endpoint node copies the next 128-bit Segment List entry
nt LNFL bits of the Argument with zeros. Otherwise (if the Argument value is 0), from the SRH to the Destination Address field of the IPv6 header.</t>
the SR segment endpoint node copies the next 128-bit Segment List entry from th <section anchor="sec-next-end">
e SRH to the Destination Address field of the IPv6 header.</t> <name>End with NEXT-CSID</name>
<t>When processing an IPv6 packet that matches a FIB entry locally ins
tantiated as an End SID with the NEXT-CSID flavor, the procedure described in <x
ref target="RFC8986" sectionFormat="of" section="4.1"/> is executed with the fol
lowing modifications.</t>
<section anchor="sec-next-end"><name>End with NEXT-CSID</name> <!--[rfced] This list is a bit difficult to follow. How may we update
for parallel structure (and the ease of the reader)?
Specifically, please clarify the "whichever comes first" (we have
omitted that from our suggested text). Note that a similar
sentence occurs near the end of Section 4.1.2, 4.1.3, 4.1.4, 4.1.6, as wel
l.
<t>When processing an IPv6 packet that matches a FIB entry locally instantiated Original:
as an End SID with the NEXT-CSID flavor, the procedure described in Section 4.1 In addition, this pseudocode is executed before processing any
of <xref target="RFC8986"/> is executed with the following modifications.</t> extension header that is not an SRH, a Hop-by-Hop header or a
Destination Options header, or before processing the upper-layer
header, whichever comes first.
<t>The below pseudocode is inserted between lines S01 and S02 of the SRH process Perhaps:
ing in Section 4.1 of <xref target="RFC8986"/>. In addition, this pseudocode is In addition, this pseudocode is executed before processing:
executed before processing any extension header that is not an SRH, a Hop-by-Hop
header or a Destination Options header, or before processing the upper-layer he
ader, whichever comes first.</t>
<figure><artwork><![CDATA[ * any extension header that is not an SRH,
* a Hop-by-Hop header or a Destination Options header, or
* the upper-layer header.
-->
<t>The below pseudocode is inserted between lines S01 and S02 of the S
RH processing in <xref target="RFC8986" sectionFormat="of" section="4.1"/>. In a
ddition, this pseudocode is executed before processing any extension header that
is not an SRH, a Hop-by-Hop header or a Destination Options header, or before p
rocessing the upper-layer header, whichever comes first.</t>
<sourcecode type="pseudocode"><![CDATA[
N01. If (DA.Argument != 0) { N01. If (DA.Argument != 0) {
N02. If (IPv6 Hop Limit <= 1) { N02. If (IPv6 Hop Limit <= 1) {
N03. Send an ICMP Time Exceeded message to the Source Address, N03. Send an ICMP Time Exceeded message to the Source Address,
Code 0 (Hop limit exceeded in transit), Code 0 (Hop limit exceeded in transit),
interrupt packet processing and discard the packet. interrupt packet processing and discard the packet.
N04. } N04. }
N05. Copy DA.Argument into the bits [LBL..(LBL+AL-1)] of the N05. Copy DA.Argument into the bits [LBL..(LBL+AL-1)] of the
Destination Address. Destination Address.
N06. Set the bits [(LBL+AL)..127] of the Destination Address to N06. Set the bits [(LBL+AL)..127] of the Destination Address to
zero. zero.
N07. Decrement IPv6 Hop Limit by 1. N07. Decrement IPv6 Hop Limit by 1.
N08. Submit the packet to the egress IPv6 FIB lookup for N08. Submit the packet to the egress IPv6 FIB lookup for
transmission to the next destination. transmission to the next destination.
N09. } N09. }
]]></artwork></figure> ]]></sourcecode>
<aside>
<aside> <t>Notes:</t>
<t>Notes:</t> <ul spacing="normal">
<li>
<t><list style="symbols"> <t><tt>DA.Argument</tt> identifies the value contained in the bi
<t><spanx style="verb">DA.Argument</spanx> identifies the value contained in ts <tt>[(LBL+LNFL)..127]</tt> in the Destination Address of the IPv6 header.</t>
the bits <spanx style="verb">[(LBL+LNFL)..127]</spanx> in the Destination Addre </li>
ss of the IPv6 header.</t>
<t>The value in the Segments Left field of the SRH is not modified when <spa
nx style="verb">DA.Argument</spanx> in the received packet has a non-zero value.
</t>
</list></t>
</aside>
<t>A rendering of the complete pseudocode is provided in <xref target="sec-next-
end-complete"/>.</t>
</section>
<section anchor="sec-next-endx"><name>End.X with NEXT-CSID</name>
<t>When processing an IPv6 packet that matches a FIB entry locally instantiated
as an End.X SID with the NEXT-CSID flavor, the procedure described in Section 4.
2 of <xref target="RFC8986"/> is executed with the following modifications.</t>
<t>The pseudocode in <xref target="sec-next-end"/> of this document is modified
by replacing line N08 as shown below.</t>
<figure><artwork><![CDATA[ <li>
<t>The value in the Segments Left field of the SRH is not modifi
ed when <tt>DA.Argument</tt> in the received packet has a non-zero value.</t>
</li>
</ul>
</aside>
<t>A rendering of the complete pseudocode is provided in <xref target=
"sec-next-end-complete"/>.</t>
</section>
<section anchor="sec-next-endx">
<name>End.X with NEXT-CSID</name>
<t>When processing an IPv6 packet that matches a FIB entry locally ins
tantiated as an End.X SID with the NEXT-CSID flavor, the procedure described in
<xref target="RFC8986" sectionFormat="of" section="4.2"/> is executed with the f
ollowing modifications.</t>
<t>The pseudocode in <xref target="sec-next-end"/> of this document is
modified by replacing line N08 as shown below.</t>
<sourcecode type="pseudocode"><![CDATA[
N08. Submit the packet to the IPv6 module for transmission to the N08. Submit the packet to the IPv6 module for transmission to the
new destination via a member of J. new destination via a member of J.
]]></artwork></figure> ]]></sourcecode>
<aside>
<aside> <t>Note: the variable J is defined in <xref target="RFC8986" section
<t>Note: the variable J is defined in Section 4.2 of <xref target="RFC8986"/>. Format="of" section="4.2"/>.</t>
</t> </aside>
</aside>
<t>The resulting pseudocode is inserted between lines S01 and S02 of the SRH pro
cessing in Section 4.1 of <xref target="RFC8986"/> after applying the modificati
on described in Section 4.2 of <xref target="RFC8986"/>. In addition, this pseud
ocode is executed before processing any extension header that is not an SRH, a H
op-by-Hop header or a Destination Options header, or before processing the upper
-layer header, whichever comes first.</t>
<t>A rendering of the complete pseudocode is provided in <xref target="sec-next-
endx-complete"/>.</t>
</section>
<section anchor="sec-next-endt"><name>End.T with NEXT-CSID</name>
<t>When processing an IPv6 packet that matches a FIB entry locally instantiated
as an End.T SID with the NEXT-CSID flavor, the procedure described in Section 4.
3 of <xref target="RFC8986"/> is executed with the following modifications.</t>
<t>The pseudocode in <xref target="sec-next-end"/> of this document is modified
by replacing line N08 as shown below.</t>
<figure><artwork><![CDATA[ <t>The resulting pseudocode is inserted between lines S01 and S02 of t
he SRH processing in <xref target="RFC8986" sectionFormat="of" section="4.1"/> a
fter applying the modification described in <xref target="RFC8986" sectionFormat
="of" section="4.2"/>. In addition, this pseudocode is executed before processin
g any extension header that is not an SRH, a Hop-by-Hop header or a Destination
Options header, or before processing the upper-layer header, whichever comes fir
st.</t>
<t>A rendering of the complete pseudocode is provided in <xref target=
"sec-next-endx-complete"/>.</t>
</section>
<section anchor="sec-next-endt">
<name>End.T with NEXT-CSID</name>
<t>When processing an IPv6 packet that matches a FIB entry locally ins
tantiated as an End.T SID with the NEXT-CSID flavor, the procedure described in
<xref target="RFC8986" sectionFormat="of" section="4.3"/> is executed with the f
ollowing modifications.</t>
<t>The pseudocode in <xref target="sec-next-end"/> of this document is
modified by replacing line N08 as shown below.</t>
<sourcecode type="pseudocode"><![CDATA[
N08.1. Set the packet's associated FIB table to T. N08.1. Set the packet's associated FIB table to T.
N08.2. Submit the packet to the egress IPv6 FIB lookup for N08.2. Submit the packet to the egress IPv6 FIB lookup for
transmission to the new destination. transmission to the new destination.
]]></artwork></figure> ]]></sourcecode>
<aside>
<aside> <t>Note: the variable T is defined in <xref target="RFC8986" section
<t>Note: the variable T is defined in Section 4.3 of <xref target="RFC8986"/>. Format="of" section="4.3"/>.</t>
</t> </aside>
</aside> <t>The resulting pseudocode is inserted between lines S01 and S02 of t
he SRH processing in <xref target="RFC8986" sectionFormat="of" section="4.1"/> a
<t>The resulting pseudocode is inserted between lines S01 and S02 of the SRH pro fter applying the modification described in <xref target="RFC8986" sectionFormat
cessing in Section 4.1 of <xref target="RFC8986"/> after applying the modificati ="of" section="4.3"/>. In addition, this pseudocode is executed before processin
on described in Section 4.3 of <xref target="RFC8986"/>. In addition, this pseud g any extension header that is not an SRH, a Hop-by-Hop header or a Destination
ocode is executed before processing any extension header that is not an SRH, a H Options header, or before processing the upper-layer header, whichever comes fir
op-by-Hop header or a Destination Options header, or before processing the upper st.</t>
-layer header, whichever comes first.</t> <t>A rendering of the complete pseudocode is provided in <xref target=
"sec-next-endt-complete"/>.</t>
<t>A rendering of the complete pseudocode is provided in <xref target="sec-next- </section>
endt-complete"/>.</t> <section anchor="sec-next-endb6">
<name>End.B6.Encaps with NEXT-CSID</name>
</section> <t>When processing an IPv6 packet that matches a FIB entry locally ins
<section anchor="sec-next-endb6"><name>End.B6.Encaps with NEXT-CSID</name> tantiated as an End.B6.Encaps SID with the NEXT-CSID flavor, the procedure descr
ibed in <xref target="RFC8986" sectionFormat="of" section="4.13"/> is executed w
<t>When processing an IPv6 packet that matches a FIB entry locally instantiated ith the following modifications.</t>
as an End.B6.Encaps SID with the NEXT-CSID flavor, the procedure described in Se <t>The pseudocode in <xref target="sec-next-end"/> of this document is
ction 4.13 of <xref target="RFC8986"/> is executed with the following modificati modified by replacing line N08 as shown below.</t>
ons.</t> <sourcecode type="pseudocode"><![CDATA[
<t>The pseudocode in <xref target="sec-next-end"/> of this document is modified
by replacing line N08 as shown below.</t>
<figure><artwork><![CDATA[
N08.1. Push a new IPv6 header with its own SRH containing B. N08.1. Push a new IPv6 header with its own SRH containing B.
N08.2. Set the outer IPv6 SA to A. N08.2. Set the outer IPv6 SA to A.
N08.3. Set the outer IPv6 DA to the first SID of B. N08.3. Set the outer IPv6 DA to the first SID of B.
N08.4. Set the outer Payload Length, Traffic Class, Flow Label, N08.4. Set the outer Payload Length, Traffic Class, Flow Label,
Hop Limit, and Next Header fields. Hop Limit, and Next Header fields.
N08.5. Submit the packet to the egress IPv6 FIB lookup for N08.5. Submit the packet to the egress IPv6 FIB lookup for
transmission to the next destination. transmission to the next destination.
]]></artwork></figure> ]]></sourcecode>
<aside>
<aside> <t>Note: the variables A and B, as well as the values of the Payload
<t>Note: the variables A and B, as well as the values of the Payload Length, T Length, Traffic Class, Flow Label, Hop Limit, and Next Header are defined in <x
raffic Class, Flow Label, Hop Limit, and Next Header are defined in Section 4.13 ref target="RFC8986" sectionFormat="of" section="4.13"/>.</t>
of <xref target="RFC8986"/>.</t> </aside>
</aside> <t>The resulting pseudocode is inserted between lines S01 and S02 of t
he SRH processing in <xref target="RFC8986" sectionFormat="of" section="4.13"/>.
<t>The resulting pseudocode is inserted between lines S01 and S02 of the SRH pro In addition, this pseudocode is executed before processing any extension header
cessing in Section 4.13 of <xref target="RFC8986"/>. In addition, this pseudocod that is not an SRH, a Hop-by-Hop header or a Destination Options header, or bef
e is executed before processing any extension header that is not an SRH, a Hop-b ore processing the upper-layer header, whichever comes first.</t>
y-Hop header or a Destination Options header, or before processing the upper-lay <t>A rendering of the complete pseudocode is provided in <xref target=
er header, whichever comes first.</t> "sec-next-endb6-complete"/>.</t>
<t>Similar to the base End.B6.Encaps SID defined in <xref target="RFC8
<t>A rendering of the complete pseudocode is provided in <xref target="sec-next- 986" sectionFormat="of" section="4.13"/>, the NEXT-CSID flavor variant updates t
endb6-complete"/>.</t> he Destination Address field of the inner IPv6 header to the next SID in the ori
ginal segment list before encapsulating the packet with the segment list of SR P
<t>Similar to the base End.B6.Encaps SID defined in Section 4.13 of <xref target olicy B. At the endpoint of SR Policy B, the encapsulation is removed and the in
="RFC8986"/>, the NEXT-CSID flavor variant updates the Destination Address field ner packet is forwarded towards the exposed destination address, which already c
of the inner IPv6 header to the next SID in the original segment list before en ontains the next SID in the original segment list.</t>
capsulating the packet with the segment list of SR Policy B. At the endpoint of </section>
SR Policy B, the encapsulation is removed and the inner packet is forwarded towa <section anchor="sec-next-endb6red">
rds the exposed destination address, which already contains the next SID in the <name>End.B6.Encaps.Red with NEXT-CSID</name>
original segment list.</t> <t>This is an optimization of the End.B6.Encaps with NEXT-CSID behavio
r.</t>
</section> <t>When processing an IPv6 packet that matches a FIB entry locally ins
<section anchor="sec-next-endb6red"><name>End.B6.Encaps.Red with NEXT-CSID</name tantiated as an End.B6.Encaps.Red SID with the NEXT-CSID flavor, the procedure d
> escribed in <xref target="sec-next-endb6"/> of this document is executed with th
e modifications in <xref target="RFC8986" sectionFormat="of" section="4.14"/>.</
<t>This is an optimization of the End.B6.Encaps with NEXT-CSID behavior.</t> t>
</section>
<t>When processing an IPv6 packet that matches a FIB entry locally instantiated <section anchor="sec-next-endbm">
as an End.B6.Encaps.Red SID with the NEXT-CSID flavor, the procedure described i <name>End.BM with NEXT-CSID</name>
n <xref target="sec-next-endb6"/> of this document is executed with the modifica <t>When processing an IPv6 packet that matches a FIB entry locally ins
tions in Section 4.14 of <xref target="RFC8986"/>.</t> tantiated as an End.BM SID with the NEXT-CSID flavor, the procedure described in
<xref target="RFC8986" sectionFormat="of" section="4.15"/> is executed with the
</section> following modifications.</t>
<section anchor="sec-next-endbm"><name>End.BM with NEXT-CSID</name> <t>The pseudocode in <xref target="sec-next-end"/> of this document is
modified by replacing line N08 as shown below.</t>
<t>When processing an IPv6 packet that matches a FIB entry locally instantiated <sourcecode type="pseudocode"><![CDATA[
as an End.BM SID with the NEXT-CSID flavor, the procedure described in Section 4
.15 of <xref target="RFC8986"/> is executed with the following modifications.</t
>
<t>The pseudocode in <xref target="sec-next-end"/> of this document is modified
by replacing line N08 as shown below.</t>
<figure><artwork><![CDATA[
N08.1. Push the MPLS label stack for B. N08.1. Push the MPLS label stack for B.
N08.2. Submit the packet to the MPLS engine for transmission. N08.2. Submit the packet to the MPLS engine for transmission.
]]></artwork></figure> ]]></sourcecode>
<aside>
<aside> <t>Note: the variable B is defined in <xref target="RFC8986" section
<t>Note: the variable B is defined in Section 4.15 of <xref target="RFC8986"/> Format="of" section="4.15"/>.</t>
.</t> </aside>
</aside> <t>The resulting pseudocode is inserted between lines S01 and S02 of t
he SRH processing in <xref target="RFC8986" sectionFormat="of" section="4.15"/>.
<t>The resulting pseudocode is inserted between lines S01 and S02 of the SRH pro In addition, this pseudocode is executed before processing any extension header
cessing in Section 4.15 of <xref target="RFC8986"/>. In addition, this pseudocod that is not an SRH, a Hop-by-Hop header or a Destination Options header, or bef
e is executed before processing any extension header that is not an SRH, a Hop-b ore processing the upper-layer header, whichever comes first.</t>
y-Hop header or a Destination Options header, or before processing the upper-lay <t>A rendering of the complete pseudocode is provided in <xref target=
er header, whichever comes first.</t> "sec-next-endbm-complete"/>.</t>
</section>
<t>A rendering of the complete pseudocode is provided in <xref target="sec-next- <section anchor="sec-next-flavors">
endbm-complete"/>.</t> <name>Combination with PSP, USP, and USD Flavors</name>
</section>
<section anchor="sec-next-flavors"><name>Combination with PSP, USP and USD flavo
rs</name>
<t>PSP: The PSP flavor defined in Section 4.16.1 of <xref target="RFC8986"/> is
unchanged when combined with the NEXT-CSID flavor.</t>
<t>USP: The USP flavor defined in Section 4.16.2 of <xref target="RFC8986"/> is <!--[rfced] Should this instance of "USP" be "USD"? We do not see USP
unchanged when combined with the NEXT-CSID flavor.</t> in Section 4.16.3 of RFC 8986.
<t>USD: The USP flavor defined in Section 4.16.3 of <xref target="RFC8986"/> is Original:
unchanged when combined with the NEXT-CSID flavor.</t> USD: The USP flavor defined in Section 4.16.3 of [RFC8986] is
unchanged when combined with the NEXT-CSID flavor.
</section> Perhaps:
</section> USD: The USD flavor defined in Section 4.16.3 of [RFC8986] is
<section anchor="sec-replace"><name>REPLACE-CSID Flavor</name> unchanged when combined with the NEXT-CSID flavor.
<t>A CSID sequence compressed using the mechanism of the REPLACE-CSID flavor sta rts with a CSID container in fully formed 128-bit SID format. The Locator-Block of this SID is the common Locator-Block for all the CSIDs in the CSID sequence, its Locator-Node and Function are those of the first CSID, and its Argument carr ies the index of the current CSID in the current CSID container. The Argument va lue is initially 0. When more segments are present in the segment list, the CSID sequence continues with one or more CSID containers in packed format carrying t he series of subsequent CSIDs. Each container in packed format is a 128-bit Segm ent List entry split into K &quot;positions&quot; of LNFL bits, where K is compu ted as floor(128/LNFL). If LNFL does not divide into 128 perfectly, a zero pad i s added in the least significant bits of the CSID container to fill the bits lef t over. The second CSID in the CSID sequence is encoded in the least significant bit position of the first CSID container in packed format (position K-1), the t hird CSID is encoded in position K-2, and so on.</t> -->
<t>The last CSID in the CSID sequence is not required to have the REPLACE-CSID f <dl spacing="normal" newline="false">
lavor. It can be bound to any SRv6 endpoint behavior, including <xref target="RF <dt>PSP:</dt><dd>The PSP flavor defined in <xref target="RFC8986"
C8986"/> behaviors and NEXT-CSID flavor, as long as it meets the conditions defi sectionFormat="of" section="4.16.1"/> is unchanged when combined
ned in <xref target="sec-source-node"/>.</t> with the NEXT-CSID flavor.</dd>
<dt>USP:</dt><dd>The USP flavor defined in <xref target="RFC8986"
sectionFormat="of" section="4.16.2"/> is unchanged when combined
with the NEXT-CSID flavor.</dd>
<dt>USD:</dt><dd>The USP flavor defined in <xref target="RFC8986"
sectionFormat="of" section="4.16.3"/> is unchanged when combined
with the NEXT-CSID flavor.</dd>
</dl>
<t>The structure of a SID with the REPLACE-CSID flavor is shown in <xref target= </section>
"fig-replace-struct"/>. The same structure is also that of the CSID container fo </section>
r REPLACE-CSID in fully formed 128-bit SID format.</t> <section anchor="sec-replace">
<name>REPLACE-CSID Flavor</name>
<figure title="Structure of a REPLACE-CSID flavor SID (scaled for a 48-bit Locat <t>A CSID sequence compressed using the mechanism of the REPLACE-CSID fl
or-Block, 32-bit combined Locator-Node and Function, and 48-bit Argument)" ancho avor starts with a CSID container in fully formed 128-bit SID format. The Locato
r="fig-replace-struct"><artset><artwork type="svg"><svg xmlns="http://www.w3.or r-Block of this SID is the common Locator-Block for all the CSIDs in the CSID se
g/2000/svg" version="1.1" height="128" width="560" viewBox="0 0 560 128" class=" quence, its Locator-Node and Function are those of the first CSID, and its Argum
diagram" text-anchor="middle" font-family="monospace" font-size="13px" stroke-li ent carries the index of the current CSID in the current CSID container. The Arg
necap="round"> ument value is initially 0. When more segments are present in the segment list,
<path d="M 8,32 L 8,80" fill="none" stroke="black"/> the CSID sequence continues with one or more CSID containers in packed format ca
<path d="M 208,40 L 208,72" fill="none" stroke="black"/> rrying the series of subsequent CSIDs. Each container in packed format is a 128-
<path d="M 344,40 L 344,72" fill="none" stroke="black"/> bit Segment List entry split into K "positions" of LNFL bits, where K is compute
<path d="M 552,32 L 552,80" fill="none" stroke="black"/> d as floor(128/LNFL). If LNFL does not divide into 128 perfectly, a zero pad is
<path d="M 8,32 L 552,32" fill="none" stroke="black"/> added in the least significant bits of the CSID container to fill the bits left
<path d="M 8,80 L 552,80" fill="none" stroke="black"/> over. The second CSID in the CSID sequence is encoded in the least significant b
<path d="M 16,96 L 200,96" fill="none" stroke="black"/> it position of the first CSID container in packed format (position K-1), the thi
<path d="M 216,96 L 336,96" fill="none" stroke="black"/> rd CSID is encoded in position K-2, and so on.</t>
<path d="M 352,96 L 544,96" fill="none" stroke="black"/> <t>The last CSID in the CSID sequence is not required to have the REPLAC
<polygon class="arrowhead" points="552,96 540,90.4 540,101.6" fill="black" trans E-CSID flavor. It can be bound to any SRv6 endpoint behavior, including the beha
form="rotate(0,544,96)"/> viors described in <xref target="RFC8986"/> and NEXT-CSID flavor, as long as it
<polygon class="arrowhead" points="360,96 348,90.4 348,101.6" fill="black" trans meets the conditions defined in <xref target="sec-source-node"/>.</t>
form="rotate(180,352,96)"/> <t>The structure of a SID with the REPLACE-CSID flavor is shown in <xref
<polygon class="arrowhead" points="344,96 332,90.4 332,101.6" fill="black" trans target="fig-replace-struct"/>. The same structure is also that of the CSID cont
form="rotate(0,336,96)"/> ainer for REPLACE-CSID in fully formed 128-bit SID format.</t>
<polygon class="arrowhead" points="224,96 212,90.4 212,101.6" fill="black" trans <figure anchor="fig-replace-struct">
form="rotate(180,216,96)"/> <name>Structure of a REPLACE-CSID Flavor SID (Scaled for a 48-Bit Loca
<polygon class="arrowhead" points="208,96 196,90.4 196,101.6" fill="black" trans tor-Block, 32-Bit Combined Locator-Node and Function, and 48-Bit Argument)</name
form="rotate(0,200,96)"/> >
<polygon class="arrowhead" points="24,96 12,90.4 12,101.6" fill="black" transfor <artset>
m="rotate(180,16,96)"/> <artwork type="svg"><svg xmlns="http://www.w3.org/2000/svg" version=
<g class="text"> "1.1" height="128" width="560" viewBox="0 0 560 128" class="diagram" text-anchor
<text x="104" y="52">Locator-Block</text> ="middle" font-family="monospace" font-size="13px" stroke-linecap="round">
<text x="276" y="52">Locator-Node</text> <path d="M 8,32 L 8,80" fill="none" stroke="black"/>
<text x="444" y="52">Argument</text> <path d="M 208,40 L 208,72" fill="none" stroke="black"/>
<text x="240" y="68">+</text> <path d="M 344,40 L 344,72" fill="none" stroke="black"/>
<text x="284" y="68">Function</text> <path d="M 552,32 L 552,80" fill="none" stroke="black"/>
<text x="104" y="116">LBL</text> <path d="M 8,32 L 552,32" fill="none" stroke="black"/>
<text x="276" y="116">LNFL</text> <path d="M 8,80 L 552,80" fill="none" stroke="black"/>
<text x="444" y="116">AL</text> <path d="M 16,96 L 200,96" fill="none" stroke="black"/>
</g> <path d="M 216,96 L 336,96" fill="none" stroke="black"/>
</svg> <path d="M 352,96 L 544,96" fill="none" stroke="black"/>
</artwork><artwork type="ascii-art"><![CDATA[ <polygon class="arrowhead" points="552,96 540,90.4 540,101.6" fi
ll="black" transform="rotate(0,544,96)"/>
<polygon class="arrowhead" points="360,96 348,90.4 348,101.6" fi
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<polygon class="arrowhead" points="344,96 332,90.4 332,101.6" fi
ll="black" transform="rotate(0,336,96)"/>
<polygon class="arrowhead" points="224,96 212,90.4 212,101.6" fi
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ll="black" transform="rotate(0,200,96)"/>
<polygon class="arrowhead" points="24,96 12,90.4 12,101.6" fill=
"black" transform="rotate(180,16,96)"/>
<g class="text">
<text x="104" y="52">Locator-Block</text>
<text x="276" y="52">Locator-Node</text>
<text x="444" y="52">Argument</text>
<text x="240" y="68">+</text>
<text x="284" y="68">Function</text>
<text x="104" y="116">LBL</text>
<text x="276" y="116">LNFL</text>
<text x="444" y="116">AL</text>
</g>
</svg>
</artwork>
<artwork type="ascii-art"><![CDATA[
+-------------------------------------------------------------------+ +-------------------------------------------------------------------+
| Locator-Block | Locator-Node | Argument | | Locator-Block | Locator-Node | Argument |
| | + Function | | | | + Function | |
+-------------------------------------------------------------------+ +-------------------------------------------------------------------+
<----------------------> <--------------> <-----------------------> <----------------------> <--------------> <----------------------->
LBL LNFL AL LBL LNFL AL
]]></artwork></artset></figure> ]]></artwork>
</artset>
<t>The structure of a CSID container for REPLACE-CSID in packed format is shown </figure>
in <xref target="fig-replace-container"/>.</t> <t>The structure of a CSID container for REPLACE-CSID in packed format i
s shown in <xref target="fig-replace-container"/>.</t>
<figure title="Structure of a CSID container for REPLACE-CSID using a 32-bit CSI <figure anchor="fig-replace-container">
D length (K = 4)" anchor="fig-replace-container"><artset><artwork type="svg"><s <name>Structure of a CSID Container for REPLACE-CSID Using a 32-Bit CS
vg xmlns="http://www.w3.org/2000/svg" version="1.1" height="128" width="560" vie ID Length (K = 4)</name>
wBox="0 0 560 128" class="diagram" text-anchor="middle" font-family="monospace" <artset>
font-size="13px" stroke-linecap="round"> <artwork type="svg"><svg xmlns="http://www.w3.org/2000/svg" version=
<path d="M 8,32 L 8,80" fill="none" stroke="black"/> "1.1" height="128" width="560" viewBox="0 0 560 128" class="diagram" text-anchor
<path d="M 144,40 L 144,72" fill="none" stroke="black"/> ="middle" font-family="monospace" font-size="13px" stroke-linecap="round">
<path d="M 280,40 L 280,72" fill="none" stroke="black"/> <path d="M 8,32 L 8,80" fill="none" stroke="black"/>
<path d="M 416,40 L 416,72" fill="none" stroke="black"/> <path d="M 144,40 L 144,72" fill="none" stroke="black"/>
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<path d="M 8,80 L 552,80" fill="none" stroke="black"/> <path d="M 552,32 L 552,80" fill="none" stroke="black"/>
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<polygon class="arrowhead" points="280,96 268,90.4 268,101.6" fill="black" trans <polygon class="arrowhead" points="296,96 284,90.4 284,101.6" fi
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<polygon class="arrowhead" points="24,96 12,90.4 12,101.6" fill="black" transfor <polygon class="arrowhead" points="144,96 132,90.4 132,101.6" fi
m="rotate(180,16,96)"/> ll="black" transform="rotate(0,136,96)"/>
<g class="text"> <polygon class="arrowhead" points="24,96 12,90.4 12,101.6" fill=
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<text x="100" y="52">CSID</text> <g class="text">
<text x="192" y="52">Third</text> <text x="52" y="52">Fourth</text>
<text x="236" y="52">CSID</text> <text x="100" y="52">CSID</text>
<text x="324" y="52">Second</text> <text x="192" y="52">Third</text>
<text x="372" y="52">CSID</text> <text x="236" y="52">CSID</text>
<text x="464" y="52">First</text> <text x="324" y="52">Second</text>
<text x="508" y="52">CSID</text> <text x="372" y="52">CSID</text>
<text x="64" y="68">(position</text> <text x="464" y="52">First</text>
<text x="116" y="68">0)</text> <text x="508" y="52">CSID</text>
<text x="200" y="68">(position</text> <text x="64" y="68">(position</text>
<text x="252" y="68">1)</text> <text x="116" y="68">0)</text>
<text x="336" y="68">(position</text> <text x="200" y="68">(position</text>
<text x="388" y="68">2)</text> <text x="252" y="68">1)</text>
<text x="472" y="68">(position</text> <text x="336" y="68">(position</text>
<text x="524" y="68">3)</text> <text x="388" y="68">2)</text>
<text x="76" y="116">LNFL</text> <text x="472" y="68">(position</text>
<text x="212" y="116">LNFL</text> <text x="524" y="68">3)</text>
<text x="348" y="116">LNFL</text> <text x="76" y="116">LNFL</text>
<text x="484" y="116">LNFL</text> <text x="212" y="116">LNFL</text>
</g> <text x="348" y="116">LNFL</text>
</svg> <text x="484" y="116">LNFL</text>
</artwork><artwork type="ascii-art"><![CDATA[ </g>
</svg>
</artwork>
<artwork type="ascii-art"><![CDATA[
+-------------------------------------------------------------------+ +-------------------------------------------------------------------+
| Fourth CSID | Third CSID | Second CSID | First CSID | | Fourth CSID | Third CSID | Second CSID | First CSID |
| (position 0) | (position 1) | (position 2) | (position 3) | | (position 0) | (position 1) | (position 2) | (position 3) |
+-------------------------------------------------------------------+ +-------------------------------------------------------------------+
<--------------> <--------------> <--------------> <--------------> <--------------> <--------------> <--------------> <-------------->
LNFL LNFL LNFL LNFL LNFL LNFL LNFL LNFL
]]></artwork></artset></figure> ]]></artwork>
</artset>
<t><xref target="fig-replace-csid-list"/> illustrates a compressed SID list as c </figure>
ould be produced by an SR source node steering a packet into an SR policy SID li <t><xref target="fig-replace-csid-list"/> illustrates a compressed SID l
st of seven REPLACE-CSID flavor SIDs. All SIDs in this example have a 48-bit Loc ist as could be produced by an SR source node steering a packet into an SR polic
ator-Block, 32-bit combined Locator-Node and Function, and 48-bit Argument. The y SID list of seven REPLACE-CSID flavor SIDs. All SIDs in this example have a 48
SR source node compresses the SR policy SID list as a compressed SID list of thr -bit Locator-Block, 32-bit combined Locator-Node and Function, and 48-bit Argume
ee CSID containers. The first CSID container is in fully formed 128-bit SID form nt. The SR source node compresses the SR policy SID list as a compressed SID lis
at. It carries a Locator-Block, the first CSID, and the argument value zero. The t of three CSID containers. The first CSID container is in fully formed 128-bit
second and third CSID containers are in packed format. The second CSID containe SID format. It carries a Locator-Block, the first CSID, and the argument value z
r carries the second, third, fourth, and fifth CSIDs. The third CSID container c ero. The second and third CSID containers are in packed format. The second CSID
arries the sixth and seventh CSIDs. Since the SR source node does not use the th container carries the second, third, fourth, and fifth CSIDs. The third CSID con
ird CSID container at full capacity, it sets the 64 least significant bits to ze tainer carries the sixth and seventh CSIDs. Since the SR source node does not us
ro. The SR source node sets the IPv6 DA with the value of the first CSID contain e the third CSID container at full capacity, it sets the 64 least significant bi
er, sets the first element in the SRH Segment List with the value of the third C ts to zero. The SR source node sets the IPv6 DA with the value of the first CSID
SID container, and sets the second element of the SRH Segment List with the valu container, sets the first element in the SRH Segment List with the value of the
e of the second CSID container (the elements in the SRH Segment List appear in r third CSID container, and sets the second element of the SRH Segment List with
eversed order of their processing, as specified in Section 4.1 of <xref target=" the value of the second CSID container (the elements in the SRH Segment List app
RFC8754"/>). Without reduced SRH, the SR source node also writes the first CSID ear in reversed order of their processing, as specified in <xref target="RFC8754
container as the third element of the SRH Segment List.</t> " sectionFormat="of" section="4.1"/>). Without reduced SRH, the SR source node a
lso writes the first CSID container as the third element of the SRH Segment List
<figure title="Compressed SID list of seven REPLACE-CSID flavor SIDs with a 48-b .</t>
it Locator-Block, 32-bit combined Locator-Node and Function, and 48-bit Argument <figure anchor="fig-replace-csid-list">
" anchor="fig-replace-csid-list"><artset><artwork type="svg"><svg xmlns="http:/ <name>Compressed SID List of Seven REPLACE-CSID Flavor SIDs with a 48-
/www.w3.org/2000/svg" version="1.1" height="640" width="528" viewBox="0 0 528 64 Bit Locator-Block, 32-Bit Combined Locator-Node and Function, and 48-Bit Argumen
0" class="diagram" text-anchor="middle" font-family="monospace" font-size="13px" t</name>
stroke-linecap="round"> <artset>
<path d="M 8,64 L 8,192" fill="none" stroke="black"/> <artwork type="svg"><svg xmlns="http://www.w3.org/2000/svg" version=
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<path d="M 8,480 L 8,608" fill="none" stroke="black"/> ="middle" font-family="monospace" font-size="13px" stroke-linecap="round">
<path d="M 264,96 L 264,160" fill="none" stroke="black"/> <path d="M 8,64 L 8,192" fill="none" stroke="black"/>
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<path d="M 8,400 L 520,400" fill="none" stroke="black"/> <path d="M 8,304 L 520,304" fill="none" stroke="black"/>
<path d="M 8,480 L 520,480" fill="none" stroke="black"/> <path d="M 8,336 L 520,336" fill="none" stroke="black"/>
<path d="M 8,544 L 520,544" fill="none" stroke="black"/> <path d="M 8,368 L 520,368" fill="none" stroke="black"/>
<path d="M 8,576 L 520,576" fill="none" stroke="black"/> <path d="M 8,400 L 520,400" fill="none" stroke="black"/>
<path d="M 8,608 L 520,608" fill="none" stroke="black"/> <path d="M 8,480 L 520,480" fill="none" stroke="black"/>
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<text x="16" y="36">0</text> <path d="M 8,576 L 520,576" fill="none" stroke="black"/>
<text x="176" y="36">1</text> <path d="M 8,608 L 520,608" fill="none" stroke="black"/>
<text x="336" y="36">2</text> <g class="text">
<text x="496" y="36">3</text> <text x="16" y="36">0</text>
<text x="16" y="52">0</text> <text x="176" y="36">1</text>
<text x="32" y="52">1</text> <text x="336" y="36">2</text>
<text x="48" y="52">2</text> <text x="496" y="36">3</text>
<text x="64" y="52">3</text> <text x="16" y="52">0</text>
<text x="80" y="52">4</text> <text x="32" y="52">1</text>
<text x="96" y="52">5</text> <text x="48" y="52">2</text>
<text x="112" y="52">6</text> <text x="64" y="52">3</text>
<text x="128" y="52">7</text> <text x="80" y="52">4</text>
<text x="144" y="52">8</text> <text x="96" y="52">5</text>
<text x="160" y="52">9</text> <text x="112" y="52">6</text>
<text x="176" y="52">0</text> <text x="128" y="52">7</text>
<text x="192" y="52">1</text> <text x="144" y="52">8</text>
<text x="208" y="52">2</text> <text x="160" y="52">9</text>
<text x="224" y="52">3</text> <text x="176" y="52">0</text>
<text x="240" y="52">4</text> <text x="192" y="52">1</text>
<text x="256" y="52">5</text> <text x="208" y="52">2</text>
<text x="272" y="52">6</text> <text x="224" y="52">3</text>
<text x="288" y="52">7</text> <text x="240" y="52">4</text>
<text x="304" y="52">8</text> <text x="256" y="52">5</text>
<text x="320" y="52">9</text> <text x="272" y="52">6</text>
<text x="336" y="52">0</text> <text x="288" y="52">7</text>
<text x="352" y="52">1</text> <text x="304" y="52">8</text>
<text x="368" y="52">2</text> <text x="320" y="52">9</text>
<text x="384" y="52">3</text> <text x="336" y="52">0</text>
<text x="400" y="52">4</text> <text x="352" y="52">1</text>
<text x="416" y="52">5</text> <text x="368" y="52">2</text>
<text x="432" y="52">6</text> <text x="384" y="52">3</text>
<text x="448" y="52">7</text> <text x="400" y="52">4</text>
<text x="464" y="52">8</text> <text x="416" y="52">5</text>
<text x="480" y="52">9</text> <text x="432" y="52">6</text>
<text x="496" y="52">0</text> <text x="448" y="52">7</text>
<text x="512" y="52">1</text> <text x="464" y="52">8</text>
<text x="136" y="100">Locator-Block</text> <text x="480" y="52">9</text>
<text x="368" y="116">1st</text> <text x="496" y="52">0</text>
<text x="404" y="116">CSID</text> <text x="512" y="52">1</text>
<text x="72" y="148">1st</text> <text x="136" y="100">Locator-Block</text>
<text x="108" y="148">CSID</text> <text x="368" y="116">1st</text>
<text x="168" y="148">continued</text> <text x="404" y="116">CSID</text>
<text x="392" y="164">0</text> <text x="72" y="148">1st</text>
<text x="200" y="212">First</text> <text x="108" y="148">CSID</text>
<text x="244" y="212">CSID</text> <text x="168" y="148">continued</text>
<text x="304" y="212">container</text> <text x="392" y="164">0</text>
<text x="16" y="244">0</text> <text x="200" y="212">First</text>
<text x="176" y="244">1</text> <text x="244" y="212">CSID</text>
<text x="336" y="244">2</text> <text x="304" y="212">container</text>
<text x="496" y="244">3</text> <text x="16" y="244">0</text>
<text x="16" y="260">0</text> <text x="176" y="244">1</text>
<text x="32" y="260">1</text> <text x="336" y="244">2</text>
<text x="48" y="260">2</text> <text x="496" y="244">3</text>
<text x="64" y="260">3</text> <text x="16" y="260">0</text>
<text x="80" y="260">4</text> <text x="32" y="260">1</text>
<text x="96" y="260">5</text> <text x="48" y="260">2</text>
<text x="112" y="260">6</text> <text x="64" y="260">3</text>
<text x="128" y="260">7</text> <text x="80" y="260">4</text>
<text x="144" y="260">8</text> <text x="96" y="260">5</text>
<text x="160" y="260">9</text> <text x="112" y="260">6</text>
<text x="176" y="260">0</text> <text x="128" y="260">7</text>
<text x="192" y="260">1</text> <text x="144" y="260">8</text>
<text x="208" y="260">2</text> <text x="160" y="260">9</text>
<text x="224" y="260">3</text> <text x="176" y="260">0</text>
<text x="240" y="260">4</text> <text x="192" y="260">1</text>
<text x="256" y="260">5</text> <text x="208" y="260">2</text>
<text x="272" y="260">6</text> <text x="224" y="260">3</text>
<text x="288" y="260">7</text> <text x="240" y="260">4</text>
<text x="304" y="260">8</text> <text x="256" y="260">5</text>
<text x="320" y="260">9</text> <text x="272" y="260">6</text>
<text x="336" y="260">0</text> <text x="288" y="260">7</text>
<text x="352" y="260">1</text> <text x="304" y="260">8</text>
<text x="368" y="260">2</text> <text x="320" y="260">9</text>
<text x="384" y="260">3</text> <text x="336" y="260">0</text>
<text x="400" y="260">4</text> <text x="352" y="260">1</text>
<text x="416" y="260">5</text> <text x="368" y="260">2</text>
<text x="432" y="260">6</text> <text x="384" y="260">3</text>
<text x="448" y="260">7</text> <text x="400" y="260">4</text>
<text x="464" y="260">8</text> <text x="416" y="260">5</text>
<text x="480" y="260">9</text> <text x="432" y="260">6</text>
<text x="496" y="260">0</text> <text x="448" y="260">7</text>
<text x="512" y="260">1</text> <text x="464" y="260">8</text>
<text x="240" y="292">5th</text> <text x="480" y="260">9</text>
<text x="276" y="292">CSID</text> <text x="496" y="260">0</text>
<text x="240" y="324">4th</text> <text x="512" y="260">1</text>
<text x="276" y="324">CSID</text> <text x="240" y="292">5th</text>
<text x="240" y="356">3rd</text> <text x="276" y="292">CSID</text>
<text x="276" y="356">CSID</text> <text x="240" y="324">4th</text>
<text x="240" y="388">2nd</text> <text x="276" y="324">CSID</text>
<text x="276" y="388">CSID</text> <text x="240" y="356">3rd</text>
<text x="204" y="420">Second</text> <text x="276" y="356">CSID</text>
<text x="252" y="420">CSID</text> <text x="240" y="388">2nd</text>
<text x="312" y="420">container</text> <text x="276" y="388">CSID</text>
<text x="16" y="452">0</text> <text x="204" y="420">Second</text>
<text x="176" y="452">1</text> <text x="252" y="420">CSID</text>
<text x="336" y="452">2</text> <text x="312" y="420">container</text>
<text x="496" y="452">3</text> <text x="16" y="452">0</text>
<text x="16" y="468">0</text> <text x="176" y="452">1</text>
<text x="32" y="468">1</text> <text x="336" y="452">2</text>
<text x="48" y="468">2</text> <text x="496" y="452">3</text>
<text x="64" y="468">3</text> <text x="16" y="468">0</text>
<text x="80" y="468">4</text> <text x="32" y="468">1</text>
<text x="96" y="468">5</text> <text x="48" y="468">2</text>
<text x="112" y="468">6</text> <text x="64" y="468">3</text>
<text x="128" y="468">7</text> <text x="80" y="468">4</text>
<text x="144" y="468">8</text> <text x="96" y="468">5</text>
<text x="160" y="468">9</text> <text x="112" y="468">6</text>
<text x="176" y="468">0</text> <text x="128" y="468">7</text>
<text x="192" y="468">1</text> <text x="144" y="468">8</text>
<text x="208" y="468">2</text> <text x="160" y="468">9</text>
<text x="224" y="468">3</text> <text x="176" y="468">0</text>
<text x="240" y="468">4</text> <text x="192" y="468">1</text>
<text x="256" y="468">5</text> <text x="208" y="468">2</text>
<text x="272" y="468">6</text> <text x="224" y="468">3</text>
<text x="288" y="468">7</text> <text x="240" y="468">4</text>
<text x="304" y="468">8</text> <text x="256" y="468">5</text>
<text x="320" y="468">9</text> <text x="272" y="468">6</text>
<text x="336" y="468">0</text> <text x="288" y="468">7</text>
<text x="352" y="468">1</text> <text x="304" y="468">8</text>
<text x="368" y="468">2</text> <text x="320" y="468">9</text>
<text x="384" y="468">3</text> <text x="336" y="468">0</text>
<text x="400" y="468">4</text> <text x="352" y="468">1</text>
<text x="416" y="468">5</text> <text x="368" y="468">2</text>
<text x="432" y="468">6</text> <text x="384" y="468">3</text>
<text x="448" y="468">7</text> <text x="400" y="468">4</text>
<text x="464" y="468">8</text> <text x="416" y="468">5</text>
<text x="480" y="468">9</text> <text x="432" y="468">6</text>
<text x="496" y="468">0</text> <text x="448" y="468">7</text>
<text x="512" y="468">1</text> <text x="464" y="468">8</text>
<text x="264" y="516">0</text> <text x="480" y="468">9</text>
<text x="240" y="564">7th</text> <text x="496" y="468">0</text>
<text x="276" y="564">CSID</text> <text x="512" y="468">1</text>
<text x="240" y="596">6th</text> <text x="264" y="516">0</text>
<text x="276" y="596">CSID</text> <text x="240" y="564">7th</text>
<text x="200" y="628">Third</text> <text x="276" y="564">CSID</text>
<text x="244" y="628">CSID</text> <text x="240" y="596">6th</text>
<text x="304" y="628">container</text> <text x="276" y="596">CSID</text>
</g> <text x="200" y="628">Third</text>
</svg> <text x="244" y="628">CSID</text>
</artwork><artwork type="ascii-art"><![CDATA[ <text x="304" y="628">container</text>
</g>
</svg>
</artwork>
<artwork type="ascii-art"><![CDATA[
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+ Locator-Block +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + Locator-Block +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | 1st CSID | | | 1st CSID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1st CSID continued | | | 1st CSID continued | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 0 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 0 +
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
First CSID container First CSID Container
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 5th CSID | | 5th CSID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 4th CSID | | 4th CSID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 3rd CSID | | 3rd CSID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 2nd CSID | | 2nd CSID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Second CSID container Second CSID Container
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
+ 0 + + 0 +
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 7th CSID | | 7th CSID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 6th CSID | | 6th CSID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Third CSID container Third CSID Container
]]></artwork></artset></figure> ]]></artwork>
</artset>
<t>This document updates <xref target="RFC8754"/> by allowing each entry in the </figure>
SRH Segment List to be either an IPv6 address or a REPLACE-CSID container in pac <t>This document updates <xref target="RFC8754"/> by allowing each entry
ked format. The SRv6 endpoint behaviors specified herein ensure that this entry in the SRH Segment List to be either an IPv6 address or a REPLACE-CSID containe
is never copied as is to the IPv6 header and that the Destination Address field r in packed format. The SRv6 endpoint behaviors specified herein ensure that thi
of the IPv6 header is always a valid SRv6 SID conforming to <xref target="RFC960 s entry is never copied as is to the IPv6 header and that the Destination Addres
2"/>.</t> s field of the IPv6 header is always a valid SRv6 SID conforming to <xref target
="RFC9602"/>.</t>
<t>The REPLACE-CSID flavor SIDs support any Locator-Block length (LBL), dependin <t>The REPLACE-CSID flavor SIDs support any Locator-Block length (LBL),
g on the needs of the operator, as long as it does not exceed 128-LNFL-ceiling(l depending on the needs of the operator, as long as it does not exceed 128-LNFL-c
og_2(128/LNFL)) (ceiling(x) is the least integer greater than or equal to x <xre eiling(log_2(128/LNFL)) (ceiling(x) is the least integer greater than or equal t
f target="GKP94"/>), so that enough bits remain available for the CSID and Argum o x <xref target="GKP94"/>), so that enough bits remain available for the CSID a
ent. A Locator-Block length of 48, 56, 64, 72, or 80 bits is recommended for eas nd Argument. A Locator-Block length of 48, 56, 64, 72, or 80 bits is recommended
ier reading in operation.</t> for easier reading in operation.</t>
<t>This document defines the REPLACE-CSID flavor for 16-bit and 32-bit C
<t>This document defines the REPLACE-CSID flavor for 16-bit and 32-bit CSID leng SID lengths (LNFL). An implementation <bcp14>MUST</bcp14> support a 32-bit CSID
ths (LNFL). An implementation MUST support a 32-bit CSID length for REPLACE-CSID length for REPLACE-CSID flavor SIDs.</t>
flavor SIDs.</t> <t>The Argument length (AL) for REPLACE-CSID flavor SIDs is equal to 128
-LBL-LNFL. The index value is encoded in the least significant X bits of the Arg
<t>The Argument length (AL) for REPLACE-CSID flavor SIDs is equal to 128-LBL-LNF ument, where X is computed as ceiling(log_2(128/LNFL)).</t>
L. The index value is encoded in the least significant X bits of the Argument, w <t>When processing an IPv6 packet that matches a FIB entry locally insta
here X is computed as ceiling(log_2(128/LNFL)).</t> ntiated as a SID with the REPLACE-CSID flavor, the SR segment endpoint node appl
ies the procedure specified in the following subsection that corresponds to the
<t>When processing an IPv6 packet that matches a FIB entry locally instantiated SID behavior. If the SID also has the PSP, USP, or USD flavor, the procedure is
as a SID with the REPLACE-CSID flavor, the SR segment endpoint node applies the modified as described in <xref target="sec-replace-flavors"/>.</t>
procedure specified in the following subsection that corresponds to the SID beha <t>At a high level, at the start of a CSID sequence using the REPLACE-CS
vior. If the SID also has the PSP, USP, or USD flavor, the procedure is modified ID flavor, the first CSID container in fully formed 128-bit SID format is copied
as described in <xref target="sec-replace-flavors"/>.</t> to the Destination Address of the IPv6 header. Then, for any SID with the REPLA
CE-CSID flavor, the SR segment endpoint node determines the next SID of the SID
<t>At a high level, at the start of a CSID sequence using the REPLACE-CSID flavo list as follows. When an SRH is present, the SR segment endpoint node decrements
r, the first CSID container in fully formed 128-bit SID format is copied to the the index value in the Argument of the active SID if the index value is not 0 o
Destination Address of the IPv6 header. Then, for any SID with the REPLACE-CSID r, if it is 0, decrements the Segments Left value in the SRH and sets the index
flavor, the SR segment endpoint node determines the next SID of the SID list as value in the Argument of the active SID to K-1. The updated index value indicate
follows. When an SRH is present, the SR segment endpoint node decrements the ind s the position of the next CSID within the CSID container in packed format at th
ex value in the Argument of the active SID if the index value is not 0 or, if it e "Segment List" index "Segments Left" in the SRH. The SR segment endpoint node
is 0, decrements the Segments Left value in the SRH and sets the index value in then constructs the next SID by copying this next CSID to the bits that immediat
the Argument of the active SID to K-1. The updated index value indicates the po ely follow the Locator-Block in the Destination Address field of the IPv6 header
sition of the next CSID within the CSID container in packed format at the &quot; , thus overwriting the active SID Locator-Node and Function with those of the ne
Segment List&quot; index &quot;Segments Left&quot; in the SRH. The SR segment en xt CSID. If no SRH is present, the SR segment endpoint node ignores the index va
dpoint node then constructs the next SID by copying this next CSID to the bits t lue in the SID Argument (except End.DT2M, see <xref target="sec-replace-enddx"/>
hat immediately follow the Locator-Block in the Destination Address field of the ) and processes the upper-layer header as per <xref target="RFC8986"/>. The CSID
IPv6 header, thus overwriting the active SID Locator-Node and Function with tho sequence ends with a last CSID in the last CSID container that does not have th
se of the next CSID. If no SRH is present, the SR segment endpoint node ignores e REPLACE-CSID flavor, or with the special CSID value 0, or when reaching the en
the index value in the SID Argument (except End.DT2M, see <xref target="sec-repl d of the segment list, whichever comes first.</t>
ace-enddx"/>) and processes the upper-layer header as per <xref target="RFC8986" <section anchor="sec-replace-end">
/>. The CSID sequence ends with a last CSID in the last CSID container that does <name>End with REPLACE-CSID</name>
not have the REPLACE-CSID flavor, or with the special CSID value 0, or when rea <t>When processing an IPv6 packet that matches a FIB entry locally ins
ching the end of the segment list, whichever comes first.</t> tantiated as an End SID with the REPLACE-CSID flavor, the SRH processing describ
ed in <xref target="RFC8986" sectionFormat="of" section="4.1"/> is executed with
<section anchor="sec-replace-end"><name>End with REPLACE-CSID</name> the following modifications.</t>
<t>Line S02 of SRH processing in <xref target="RFC8986" sectionFormat=
<t>When processing an IPv6 packet that matches a FIB entry locally instantiated "of" section="4.1"/> is replaced as follows.</t>
as an End SID with the REPLACE-CSID flavor, the SRH processing described in Sect <sourcecode type="pseudocode"><![CDATA[
ion 4.1 of <xref target="RFC8986"/> is executed with the following modifications
.</t>
<t>Line S02 of SRH processing in Section 4.1 of <xref target="RFC8986"/> is repl
aced as follows.</t>
<figure><artwork><![CDATA[
S02. If (Segments Left == 0 and (DA.Arg.Index == 0 or S02. If (Segments Left == 0 and (DA.Arg.Index == 0 or
Segment List[0][DA.Arg.Index-1] == 0)) { Segment List[0][DA.Arg.Index-1] == 0)) {
]]></artwork></figure> ]]></sourcecode>
<t>Lines S09 to S15 are replaced by the following pseudo code.</t>
<t>Lines S09 to S15 are replaced by the following pseudo code.</t> <sourcecode type="pseudocode"><![CDATA[
<figure><artwork><![CDATA[
R01. If (DA.Arg.Index != 0) { R01. If (DA.Arg.Index != 0) {
R02. If ((Last Entry > max_LE) or (Segments Left > Last Entry)) { R02. If ((Last Entry > max_LE) or (Segments Left > Last Entry)) {
R03. Send an ICMP Parameter Problem to the Source Address, R03. Send an ICMP Parameter Problem to the Source Address,
Code 0 (Erroneous header field encountered), Code 0 (Erroneous header field encountered),
Pointer set to the Segments Left field, Pointer set to the Segments Left field,
interrupt packet processing and discard the packet. interrupt packet processing and discard the packet.
R04. } R04. }
R05. Decrement DA.Arg.Index by 1. R05. Decrement DA.Arg.Index by 1.
R06. If (Segment List[Segments Left][DA.Arg.Index] == 0) { R06. If (Segment List[Segments Left][DA.Arg.Index] == 0) {
R07. Decrement Segments Left by 1. R07. Decrement Segments Left by 1.
skipping to change at line 882 skipping to change at line 890
R15. } R15. }
R16. Decrement Segments Left by 1. R16. Decrement Segments Left by 1.
R17. Set DA.Arg.Index to (floor(128/LNFL) - 1). R17. Set DA.Arg.Index to (floor(128/LNFL) - 1).
R18. } R18. }
R19. Decrement IPv6 Hop Limit by 1. R19. Decrement IPv6 Hop Limit by 1.
R20. Write Segment List[Segments Left][DA.Arg.Index] into the bits R20. Write Segment List[Segments Left][DA.Arg.Index] into the bits
[LBL..LBL+LNFL-1] of the Destination Address of the IPv6 [LBL..LBL+LNFL-1] of the Destination Address of the IPv6
header. header.
R21. Submit the packet to the egress IPv6 FIB lookup for R21. Submit the packet to the egress IPv6 FIB lookup for
transmission to the new destination. transmission to the new destination.
]]></artwork></figure> ]]></sourcecode>
<aside>
<aside> <t>Notes:</t>
<t>Notes:</t> <ul spacing="normal">
<li>
<t><list style="symbols"> <t><tt>DA.Arg.Index</tt> identifies the value contained in the b
<t><spanx style="verb">DA.Arg.Index</spanx> identifies the value contained i its <tt>[(128-ceiling(log_2(128/LNFL)))..127]</tt> in the Destination Address of
n the bits <spanx style="verb">[(128-ceiling(log_2(128/LNFL)))..127]</spanx> in the IPv6 header.</t>
the Destination Address of the IPv6 header.</t> </li>
<t><spanx style="verb">Segment List[Segments Left][DA.Arg.Index]</spanx> ide <li>
ntifies the value contained in the bits <spanx style="verb">[DA.Arg.Index*LNFL.. <t><tt>Segment List[Segments Left][DA.Arg.Index]</tt> identifies
(DA.Arg.Index+1)*LNFL-1]</spanx> in the SRH Segment List entry at index Segments the value contained in the bits <tt>[DA.Arg.Index*LNFL..(DA.Arg.Index+1)*LNFL-1
Left.</t> ]</tt> in the SRH Segment List entry at index Segments Left.</t>
</list></t> </li>
</aside> </ul>
</aside>
<t>The upper-layer header processing described in Section 4.1.1 of <xref target= <t>The upper-layer header processing described in <xref target="RFC898
"RFC8986"/> is unchanged.</t> 6" sectionFormat="of" section="4.1.1"/> is unchanged.</t>
<t>A rendering of the complete pseudocode is provided in <xref target=
<t>A rendering of the complete pseudocode is provided in <xref target="sec-repla "sec-replace-end-complete"/>.</t>
ce-end-complete"/>.</t> </section>
<section anchor="sec-replace-endx">
</section> <name>End.X with REPLACE-CSID</name>
<section anchor="sec-replace-endx"><name>End.X with REPLACE-CSID</name> <t>When processing an IPv6 packet that matches a FIB entry locally ins
tantiated as an End.X SID with the REPLACE-CSID flavor, the procedure described
<t>When processing an IPv6 packet that matches a FIB entry locally instantiated in <xref target="RFC8986" sectionFormat="of" section="4.2"/> is executed with th
as an End.X SID with the REPLACE-CSID flavor, the procedure described in Section e following modifications.</t>
4.2 of <xref target="RFC8986"/> is executed with the following modifications.</ <t>The pseudocode in <xref target="sec-replace-end"/> of this document
t> is modified by replacing lines R10 and R21 as shown below.</t>
<sourcecode type="pseudocode"><![CDATA[
<t>The pseudocode in <xref target="sec-replace-end"/> of this document is modifi
ed by replacing lines R10 and R21 as shown below.</t>
<figure><artwork><![CDATA[
R10. Submit the packet to the IPv6 module for transmission to the R10. Submit the packet to the IPv6 module for transmission to the
new destination via a member of J. new destination via a member of J.
]]></artwork></figure> ]]></sourcecode>
<sourcecode type="pseudocode"><![CDATA[
<figure><artwork><![CDATA[
R21. Submit the packet to the IPv6 module for transmission to the R21. Submit the packet to the IPv6 module for transmission to the
new destination via a member of J. new destination via a member of J.
]]></artwork></figure> ]]></sourcecode>
<aside>
<aside> <t>Note: the variable J is defined in <xref target="RFC8986" section
<t>Note: the variable J is defined in Section 4.2 of <xref target="RFC8986"/>. Format="of" section="4.2"/>.</t>
</t> </aside>
</aside> <t>The SRH processing in <xref target="RFC8986" sectionFormat="of" sec
tion="4.2"/> is replaced with the resulting pseudocode. The upper-layer header p
<t>The SRH processing in Section 4.2 of <xref target="RFC8986"/> is replaced wit rocessing is unchanged.</t>
h the resulting pseudocode. The upper-layer header processing is unchanged.</t> <t>A rendering of the complete pseudocode is provided in <xref target=
"sec-replace-endx-complete"/>.</t>
<t>A rendering of the complete pseudocode is provided in <xref target="sec-repla </section>
ce-endx-complete"/>.</t> <section anchor="sec-replace-endt">
<name>End.T with REPLACE-CSID</name>
</section> <t>When processing an IPv6 packet that matches a FIB entry locally ins
<section anchor="sec-replace-endt"><name>End.T with REPLACE-CSID</name> tantiated as an End.T SID with the REPLACE-CSID flavor, the procedure described
in <xref target="RFC8986" sectionFormat="of" section="4.3"/> is executed with th
<t>When processing an IPv6 packet that matches a FIB entry locally instantiated e following modifications.</t>
as an End.T SID with the REPLACE-CSID flavor, the procedure described in Section <t>The pseudocode in <xref target="sec-replace-end"/> of this document
4.3 of <xref target="RFC8986"/> is executed with the following modifications.</ is modified by replacing lines R10 and R21 as shown below.</t>
t> <sourcecode type="pseudocode"><![CDATA[
<t>The pseudocode in <xref target="sec-replace-end"/> of this document is modifi
ed by replacing lines R10 and R21 as shown below.</t>
<figure><artwork><![CDATA[
R10.1. Set the packet's associated FIB table to T. R10.1. Set the packet's associated FIB table to T.
R10.2. Submit the packet to the egress IPv6 FIB lookup for R10.2. Submit the packet to the egress IPv6 FIB lookup for
transmission to the new destination. transmission to the new destination.
]]></artwork></figure> ]]></sourcecode>
<sourcecode type="pseudocode"><![CDATA[
<figure><artwork><![CDATA[
R21.1. Set the packet's associated FIB table to T. R21.1. Set the packet's associated FIB table to T.
R21.2. Submit the packet to the egress IPv6 FIB lookup for R21.2. Submit the packet to the egress IPv6 FIB lookup for
transmission to the new destination. transmission to the new destination.
]]></artwork></figure> ]]></sourcecode>
<aside>
<aside> <t>Note: the variable T is defined in <xref target="RFC8986" section
<t>Note: the variable T is defined in Section 4.3 of <xref target="RFC8986"/>. Format="of" section="4.3"/>.</t>
</t> </aside>
</aside> <t>The SRH processing in <xref target="RFC8986" sectionFormat="of" sec
tion="4.3"/> is replaced with the resulting pseudocode. The upper-layer header p
<t>The SRH processing in Section 4.3 of <xref target="RFC8986"/> is replaced wit rocessing is unchanged.</t>
h the resulting pseudocode. The upper-layer header processing is unchanged.</t> <t>A rendering of the complete pseudocode is provided in <xref target=
"sec-replace-endt-complete"/>.</t>
<t>A rendering of the complete pseudocode is provided in <xref target="sec-repla </section>
ce-endt-complete"/>.</t> <section anchor="sec-replace-endb6">
<name>End.B6.Encaps with REPLACE-CSID</name>
</section> <t>When processing an IPv6 packet that matches a FIB entry locally ins
<section anchor="sec-replace-endb6"><name>End.B6.Encaps with REPLACE-CSID</name> tantiated as an End.B6.Encaps SID with the REPLACE-CSID flavor, the procedure de
scribed in <xref target="RFC8986" sectionFormat="of" section="4.13"/> is execute
<t>When processing an IPv6 packet that matches a FIB entry locally instantiated d with the following modifications.</t>
as an End.B6.Encaps SID with the REPLACE-CSID flavor, the procedure described in <t>The pseudocode in <xref target="sec-replace-end"/> of this document
Section 4.13 of <xref target="RFC8986"/> is executed with the following modific is modified by replacing lines R10 and R21 as shown below.</t>
ations.</t> <sourcecode type="pseudocode"><![CDATA[
<t>The pseudocode in <xref target="sec-replace-end"/> of this document is modifi
ed by replacing lines R10 and R21 as shown below.</t>
<figure><artwork><![CDATA[
R10.1. Push a new IPv6 header with its own SRH containing B. R10.1. Push a new IPv6 header with its own SRH containing B.
R10.2. Set the outer IPv6 SA to A. R10.2. Set the outer IPv6 SA to A.
R10.3. Set the outer IPv6 DA to the first SID of B. R10.3. Set the outer IPv6 DA to the first SID of B.
R10.4. Set the outer Payload Length, Traffic Class, Flow Label, R10.4. Set the outer Payload Length, Traffic Class, Flow Label,
Hop Limit, and Next Header fields. Hop Limit, and Next Header fields.
R10.5. Submit the packet to the egress IPv6 FIB lookup for R10.5. Submit the packet to the egress IPv6 FIB lookup for
transmission to the next destination. transmission to the next destination.
]]></artwork></figure> ]]></sourcecode>
<sourcecode type="pseudocode"><![CDATA[
<figure><artwork><![CDATA[
R21.1. Push a new IPv6 header with its own SRH containing B. R21.1. Push a new IPv6 header with its own SRH containing B.
R21.2. Set the outer IPv6 SA to A. R21.2. Set the outer IPv6 SA to A.
R21.3. Set the outer IPv6 DA to the first SID of B. R21.3. Set the outer IPv6 DA to the first SID of B.
R21.4. Set the outer Payload Length, Traffic Class, Flow Label, R21.4. Set the outer Payload Length, Traffic Class, Flow Label,
Hop Limit, and Next Header fields. Hop Limit, and Next Header fields.
R21.5. Submit the packet to the egress IPv6 FIB lookup for R21.5. Submit the packet to the egress IPv6 FIB lookup for
transmission to the next destination. transmission to the next destination.
]]></artwork></figure> ]]></sourcecode>
<aside>
<aside> <t>Note: the variables A and B, as well as the values of the Payload
<t>Note: the variables A and B, as well as the values of the Payload Length, T Length, Traffic Class, Flow Label, Hop Limit, and Next Header are defined in <x
raffic Class, Flow Label, Hop Limit, and Next Header are defined in Section 4.13 ref target="RFC8986" sectionFormat="of" section="4.13"/>.</t>
of <xref target="RFC8986"/>.</t> </aside>
</aside> <t>The SRH processing in <xref target="RFC8986" sectionFormat="of" sec
tion="4.13"/> is replaced with the resulting pseudocode. The upper-layer header
<t>The SRH processing in Section 4.13 of <xref target="RFC8986"/> is replaced wi processing is unchanged.</t>
th the resulting pseudocode. The upper-layer header processing is unchanged.</t> <t>A rendering of the complete pseudocode is provided in <xref target=
"sec-replace-endb6-complete"/>.</t>
<t>A rendering of the complete pseudocode is provided in <xref target="sec-repla </section>
ce-endb6-complete"/>.</t> <section anchor="sec-replace-endb6red">
<name>End.B6.Encaps.Red with REPLACE-CSID</name>
</section> <t>This is an optimization of the End.B6.Encaps with REPLACE-CSID beha
<section anchor="sec-replace-endb6red"><name>End.B6.Encaps.Red with REPLACE-CSID vior.</t>
</name> <t>When processing an IPv6 packet that matches a FIB entry locally ins
tantiated as an End.B6.Encaps.Red SID with the REPLACE-CSID flavor, the procedur
<t>This is an optimization of the End.B6.Encaps with REPLACE-CSID behavior.</t> e described in <xref target="sec-replace-endb6"/> of this document is executed w
ith the modifications in <xref target="RFC8986" sectionFormat="of" section="4.14
<t>When processing an IPv6 packet that matches a FIB entry locally instantiated "/>.</t>
as an End.B6.Encaps.Red SID with the REPLACE-CSID flavor, the procedure describe </section>
d in <xref target="sec-replace-endb6"/> of this document is executed with the mo <section anchor="sec-replace-endbm">
difications in Section 4.14 of <xref target="RFC8986"/>.</t> <name>End.BM with REPLACE-CSID</name>
<t>When processing an IPv6 packet that matches a FIB entry locally ins
</section> tantiated as an End.BM SID with the REPLACE-CSID flavor, the procedure described
<section anchor="sec-replace-endbm"><name>End.BM with REPLACE-CSID</name> in <xref target="RFC8986" sectionFormat="of" section="4.15"/> is executed with
the following modifications.</t>
<t>When processing an IPv6 packet that matches a FIB entry locally instantiated <t>The pseudocode in <xref target="sec-replace-end"/> of this document
as an End.BM SID with the REPLACE-CSID flavor, the procedure described in Sectio is modified by replacing lines R10 and R21 as shown below.</t>
n 4.15 of <xref target="RFC8986"/> is executed with the following modifications. <sourcecode type="pseudocode"><![CDATA[
</t>
<t>The pseudocode in <xref target="sec-replace-end"/> of this document is modifi
ed by replacing lines R10 and R21 as shown below.</t>
<figure><artwork><![CDATA[
R10.1. Push the MPLS label stack for B. R10.1. Push the MPLS label stack for B.
R10.2. Submit the packet to the MPLS engine for transmission. R10.2. Submit the packet to the MPLS engine for transmission.
]]></artwork></figure> ]]></sourcecode>
<sourcecode type="pseudocode"><![CDATA[
<figure><artwork><![CDATA[
R21.1. Push the MPLS label stack for B. R21.1. Push the MPLS label stack for B.
R21.2. Submit the packet to the MPLS engine for transmission. R21.2. Submit the packet to the MPLS engine for transmission.
]]></artwork></figure> ]]></sourcecode>
<aside>
<aside> <t>Note: the variable B is defined in <xref target="RFC8986" section
<t>Note: the variable B is defined in Section 4.15 of <xref target="RFC8986"/> Format="of" section="4.15"/>.</t>
.</t> </aside>
</aside> <t>The SRH processing in <xref target="RFC8986" sectionFormat="of" sec
tion="4.15"/> is replaced with the resulting pseudocode. The upper-layer header
<t>The SRH processing in Section 4.15 of <xref target="RFC8986"/> is replaced wi processing is unchanged.</t>
th the resulting pseudocode. The upper-layer header processing is unchanged.</t> <t>A rendering of the complete pseudocode is provided in <xref target=
"sec-replace-endbm-complete"/>.</t>
<t>A rendering of the complete pseudocode is provided in <xref target="sec-repla </section>
ce-endbm-complete"/>.</t> <section anchor="sec-replace-enddx">
<name>End.DX and End.DT with REPLACE-CSID</name>
</section> <t>When processing an IPv6 packet that matches a FIB entry locally ins
<section anchor="sec-replace-enddx"><name>End.DX and End.DT with REPLACE-CSID</n tantiated as an End.DX6, End.DX4, End.DT6, End.DT4, End.DT46, End.DX2, End.DX2V,
ame> or End.DT2U SID with the REPLACE-CSID flavor, the corresponding procedure descr
ibed in Sections <xref target="RFC8986" sectionFormat="bare" section="4.4"/> thr
<t>When processing an IPv6 packet that matches a FIB entry locally instantiated ough <xref target="RFC8986" sectionFormat="bare" section="4.11"/> of <xref targe
as an End.DX6, End.DX4, End.DT6, End.DT4, End.DT46, End.DX2, End.DX2V, or End.DT t="RFC8986"/> is executed.</t>
2U SID with the REPLACE-CSID flavor, the corresponding procedure described in Se <t>These SIDs differ from those defined in <xref target="RFC8986"/> by
ctions 4.4 through 4.11 of <xref target="RFC8986"/> is executed.</t> the presence of an Argument as part of the SID structure. The Argument value is
ignored by the SR segment endpoint node.</t>
<t>These SIDs differ from those defined in <xref target="RFC8986"/> by the prese <t>When processing an IPv6 packet that matches a FIB entry locally ins
nce of an Argument as part of the SID structure. The Argument value is ignored b tantiated as an End.DT2M SID with the REPLACE-CSID flavor, the procedure describ
y the SR segment endpoint node.</t> ed in <xref target="RFC8986" sectionFormat="of" section="4.12"/> is executed wit
h the following modification.</t>
<t>When processing an IPv6 packet that matches a FIB entry locally instantiated <t>For any End.DT2M SID with the REPLACE-CSID flavor, the value of <tt
as an End.DT2M SID with the REPLACE-CSID flavor, the procedure described in Sect >Arg.FE2</tt> is 16 bits long. The SR segment endpoint node obtains the value <t
ion 4.12 of <xref target="RFC8986"/> is executed with the following modification t>Arg.FE2</tt> from the 16 most significant bits of <tt>DA.Argument</tt> if <tt>
.</t> DA.Arg.Index</tt> is zero or from the 16 least significant bits of the next posi
tion in the current CSID container (<tt>Segment List[Segments Left][DA.Arg.Index
<t>For any End.DT2M SID with the REPLACE-CSID flavor, the value of <spanx style= -1]</tt>) otherwise (<tt>DA.Arg.Index</tt> is non-zero).</t>
"verb">Arg.FE2</spanx> is 16-bit long. The SR segment endpoint node obtains the </section>
value <spanx style="verb">Arg.FE2</spanx> from the 16 most significant bits of < <section anchor="sec-replace-flavors">
spanx style="verb">DA.Argument</spanx> if <spanx style="verb">DA.Arg.Index</span <name>Combination with PSP, USP, and USD Flavors</name>
x> is zero, or from the 16 least significant bits of the next position in the cu <t>PSP:
rrent CSID container (<spanx style="verb">Segment List[Segments Left][DA.Arg.Ind When combined with the REPLACE-CSID flavor, the additional PSP flavor instructio
ex-1]</spanx>) otherwise (<spanx style="verb">DA.Arg.Index</spanx> is non-zero). ns defined in <xref target="RFC8986" sectionFormat="of" section="4.16.1.2"/> are
</t> inserted after lines R09 and R20 of the pseudocode in <xref target="sec-replace
-end"/>, and the first line of the inserted instructions after R20 is modified a
</section> s follows.</t>
<section anchor="sec-replace-flavors"><name>Combination with PSP, USP, and USD f <sourcecode type="pseudocode"><![CDATA[
lavors</name>
<t>PSP:
When combined with the REPLACE-CSID flavor, the additional PSP flavor instructio
ns defined in Section 4.16.1.2 of <xref target="RFC8986"/> are inserted after li
nes R09 and R20 of the pseudocode in <xref target="sec-replace-end"/>, and the f
irst line of the inserted instructions after R20 is modified as follows.</t>
<figure><artwork><![CDATA[
R20.1. If (Segments Left == 0 and (DA.Arg.Index == 0 or R20.1. If (Segments Left == 0 and (DA.Arg.Index == 0 or
Segment List[0][DA.Arg.Index-1] == 0)) { Segment List[0][DA.Arg.Index-1] == 0)) {
]]></artwork></figure> ]]></sourcecode>
<aside>
<aside> <t>Note: <tt>Segment List[Segments Left][DA.Arg.Index-1]</tt> identi
<t>Note: <spanx style="verb">Segment List[Segments Left][DA.Arg.Index-1]</span fies the value contained in the bits <tt>[(DA.Arg.Index-1)*LNFL..DA.Arg.Index*LN
x> identifies the value contained in the bits <spanx style="verb">[(DA.Arg.Index FL-1]</tt> in the SRH Segment List entry at index Segments Left.</t>
-1)*LNFL..DA.Arg.Index*LNFL-1]</spanx> in the SRH Segment List entry at index Se </aside>
gments Left.</t>
</aside>
<t>USP:
When combined with the REPLACE-CSID flavor, the line S03 of the pseudocode in <x
ref target="sec-replace-end"/> are substituted by the USP flavor instructions S0
3.1 to S03.4 defined in Section 4.16.2 of <xref target="RFC8986"/>. Note that S0
3 is shown in the complete pseudocode in <xref target="sec-replace-end-complete"
/>.</t>
<t>USD:
The USD flavor defined in Section 4.16.3 of <xref target="RFC8986"/> is unchange
d when combined with the REPLACE-CSID flavor.</t>
</section>
</section>
</section>
<section anchor="csid-allocation"><name>CSID Allocation</name>
<t>The CSID value of 0 is reserved. It is used to indicate the end of a CSID con
tainer.</t>
<t>In order to efficiently manage the CSID numbering space, a deployment may div
ide it into two non-overlapping sub-spaces: a Global Identifiers Block (GIB) and
a Local Identifiers Block (LIB).</t>
<t>The CSID values that are allocated from the GIB have a global semantic within
the Locator-Block, while those that are allocated from the LIB have a local sem
antic on an SR segment endpoint node and within the scope of the Locator-Block.<
/t>
<t>The concept of LIB is applicable to SRv6 and specifically to its NEXT-CSID an
d REPLACE-CSID flavors. The shorter the CSID, the more benefit the LIB brings.</
t>
<t>The opportunity to use these sub-spaces, their size, and their CSID allocatio
n policy depends on the CSID length relative to the size of the network (e.g., n
umber of nodes, links, service routes). Some guidelines for a typical deployment
scenario are provided in the below subsections.</t>
<section anchor="global-csid"><name>Global CSID</name>
<t>A global CSID is a CSID allocated from the GIB.</t>
<t>A global CSID identifies a segment defined at the Locator-Block level. The tu
ple (Locator-Block, CSID) identifies the same segment across all nodes of the SR
domain. A typical example is a prefix segment bound to the End behavior.</t>
<t>A node can have multiple global CSIDs under the same Locator-Block (e.g., one
per IGP flexible algorithm (<xref target="RFC9350"/>)). Multiple nodes may shar
e the same global CSID (e.g., anycast <xref target="RFC4786"/>).</t>
</section>
<section anchor="local-csid"><name>Local CSID</name>
<t>A local CSID is a CSID allocated from the LIB.</t>
<t>A local CSID identifies a segment defined at the node level and within the sc
ope of a particular Locator-Block. The tuple (Locator-Block, CSID) identifies a
different segment on each node of the SR domain. A typical example is a non-rout
ed Adjacency segment bound to the End.X behavior.</t>
<t>Let N1 and N2 be two different physical nodes of the SR domain and I a local
CSID value, N1 may allocate value I to SID S1 and N2 may allocate the same value
I to SID S2.</t>
</section>
<section anchor="sec-csid-installation"><name>Recommended Installation of CSIDs
in FIB</name>
<t>Section 4.3 of <xref target="RFC8754"/> defines how an SR segment endpoint no
de identifies a locally instantiated SRv6 SID. To ensure that any valid argument
value is accepted, an SR segment endpoint node instantiating a NEXT-CSID or REP
LACE-CSID flavor SID should install a corresponding FIB entry that matches only
the Locator and Function parts of the SID (i.e., with a prefix length of LBL + L
NL + FL).</t>
<t>In addition, an SR segment endpoint node instantiating NEXT-CSID flavor SIDs
from both GIB and LIB may install combined &quot;Global + Local&quot; FIB entrie
s to match a sequence of global and local CSIDs in a single longest prefix match
(LPM) lookup.</t>
<t>For example, let us consider an SR segment endpoint node 10 instantiating the
following two NEXT-CSID flavor SIDs according to the CSID length, Locator-Block
length, and GIB/LIB recommendations in this section.</t>
<t><list style="symbols">
<t>The SID <spanx style="verb">2001:db8:b1:10::</spanx> bound to the End behav
ior with the NEXT-CSID flavor is instantiated from GIB with
<list style="symbols">
<t>Locator-Block length (LBL) = 48 (Locator-Block value <spanx style="verb
">0x20010db800b1</spanx>),</t>
<t>Locator-Node length (LNL) = 16 (Locator-Node value <spanx style="verb">
0x0010</spanx>),</t>
<t>Function length (FL) = 0, and</t>
<t>Argument length (AL) = 64.</t>
</list></t>
<t>The SID <spanx style="verb">2001:db8:b1:f123::</spanx> bound to the End.X b
ehavior for its local IGP adjacency <spanx style="verb">123</spanx> with the NEX
T-CSID flavor is instantiated from LIB with
<list style="symbols">
<t>Locator-Block length (LBL) = 48 (Locator-Block value <spanx style="verb
">0x20010db800b1</spanx>),</t>
<t>Locator-Node length (LNL) = 0,</t>
<t>Function length (FL) = 16 (Function value <spanx style="verb">0xf123</s
panx>), and</t>
<t>Argument length (AL) = 64.</t>
</list></t>
</list></t>
<t>For SID <spanx style="verb">2001:db8:b1:10::</spanx>, Node 10 would install t
he FIB entry <spanx style="verb">2001:db8:b1:10::/64</spanx> bound the End SID w
ith the NEXT-CSID flavor.</t>
<t>For SID <spanx style="verb">2001:db8:b1:f123::</spanx>, Node 10 would install
the FIB entry <spanx style="verb">2001:db8:b1:f123::/64</spanx> bound the End.X
SID for adjacency <spanx style="verb">123</spanx> with the NEXT-CSID flavor.</t
>
<t>In addition, Node 10 may also install the combined FIB entry <spanx style="ve
rb">2001:db8:b1:10:f123::/80</spanx> bound the End.X SID for adjacency <spanx st
yle="verb">123</spanx> with the NEXT-CSID flavor.</t>
<t>As another example, let us consider an SR segment endpoint node 20 instantiat
ing the following two REPLACE-CSID flavor SIDs according to the CSID length, Loc
ator-Block length, and GIB/LIB recommendations in this section.</t>
<t><list style="symbols">
<t><spanx style="verb">2001:db8:b2:20:1::</spanx> from GIB with Locator-Block
length (LBL) = 48, Locator-Node length (LNL) = 16, Function length (FL) = 16, Ar
gument length (AL) = 48, and bound to the End behavior with the REPLACE-CSID fla
vor.</t>
<t><spanx style="verb">2001:db8:b2:20:123::</spanx> from GIB with Locator-Bloc
k length (LBL) = 48, Locator-Node length (LNL) = 16, Function length (FL) = 16,
Argument length (AL) = 48, and bound to the End.X behavior for its local IGP adj
acency <spanx style="verb">123</spanx> with the REPLACE-CSID flavor.</t>
</list></t>
<t>For SID <spanx style="verb">2001:db8:b2:20:1::</spanx>, Node 20 would install
the FIB entry <spanx style="verb">2001:db8:b2:20:1::/80</spanx> bound the End S
ID with the REPLACE-CSID flavor.</t>
<t>For SID <spanx style="verb">2001:db8:b2:20:123::</spanx>, Node 20 would insta
ll the FIB entry <spanx style="verb">2001:db8:b2:20:123::/80</spanx> bound the E
nd.X SID for adjacency <spanx style="verb">123</spanx> with the REPLACE-CSID fla
vor.</t>
</section>
</section>
<section anchor="sec-source-node"><name>SR Source Node</name>
<t>An SR source node may learn from a control plane protocol (see <xref target="
sec-control-plane"/>) or local configuration the SIDs that it can use in a segme
nt list, along with their respective SRv6 endpoint behavior, structure, and any
other relevant attribute (e.g., the set of L3 adjacencies associated with an End
.X SID).</t>
<section anchor="sid-validation-for-compression"><name>SID Validation for Compre
ssion</name>
<t>As part of the compression process or as a preliminary step, the SR source no
de MUST validate the SID structure of each SID of this document in the segment l
ist. The SR source node does so regardless of whether the segment list is explic
itly configured, locally computed, or advertised by a controller (e.g., via BGP
<xref target="I-D.ietf-idr-sr-policy-safi"/> or PCEP <xref target="RFC9603"/>).<
/t>
<t>A SID structure is valid for compression if it meets all the following condit
ions.</t>
<t><list style="symbols"> <dl spacing="normal" newline="false">
<t>The Locator-Block length is not 0.</t> <dt>USP:</dt><dd>When combined with the REPLACE-CSID flavor, the
<t>The sum of the Locator-Node length and Function length is not 0.</t> line S03 of the pseudocode in <xref target="sec-replace-end"/> are
<t>The Argument length is equal to 128-LBL-LNL-FL.</t> substituted by the USP flavor instructions S03.1 to S03.4 defined
</list></t> in <xref target="RFC8986" sectionFormat="of"
section="4.16.2"/>. Note that S03 is shown in the complete
pseudocode in <xref target="sec-replace-end-complete"/>.</dd>
<dt>USD:</dt><dd>The USD flavor defined in <xref target="RFC8986"
sectionFormat="of" section="4.16.3"/> is unchanged when combined
with the REPLACE-CSID flavor.</dd>
</dl>
<t>When compressing a SID list, the SR source node MUST treat an invalid SID str </section>
ucture as unknown. A SID with an unknown SID structure is incompressible.</t> </section>
</section>
<section anchor="csid-allocation">
<name>CSID Allocation</name>
<t>The CSID value of 0 is reserved. It is used to indicate the end of a CS
ID container.</t>
<t>In order to efficiently manage the CSID numbering space, a deployment m
ay divide it into two non-overlapping sub-spaces: a Global Identifiers Block (GI
B) and a Local Identifiers Block (LIB).</t>
<t>The CSID values that are allocated from the GIB have a global semantic
within the Locator-Block, while those that are allocated from the LIB have a loc
al semantic on an SR segment endpoint node and within the scope of the Locator-B
lock.</t>
<t>The concept of LIB is applicable to SRv6 and specifically to its NEXT-C
SID and REPLACE-CSID flavors. The shorter the CSID, the more benefit the LIB bri
ngs.</t>
<t>The opportunity to use these sub-spaces, their size, and their CSID all
ocation policy depends on the CSID length relative to the size of the network (e
.g., number of nodes, links, service routes). Some guidelines for a typical depl
oyment scenario are provided in the below subsections.</t>
<section anchor="global-csid">
<name>Global CSID</name>
<t>A global CSID is a CSID allocated from the GIB.</t>
<t>A global CSID identifies a segment defined at the Locator-Block level
. The tuple (Locator-Block, CSID) identifies the same segment across all nodes o
f the SR domain. A typical example is a prefix segment bound to the End behavior
.</t>
<t>A node can have multiple global CSIDs under the same Locator-Block (e
.g., one per IGP flexible algorithm (<xref target="RFC9350"/>)). Multiple nodes
may share the same global CSID (e.g., anycast <xref target="RFC4786"/>).</t>
</section>
<section anchor="local-csid">
<name>Local CSID</name>
<t>A local CSID is a CSID allocated from the LIB.</t>
<t>A local CSID identifies a segment defined at the node level and withi
n the scope of a particular Locator-Block. The tuple (Locator-Block, CSID) ident
ifies a different segment on each node of the SR domain. A typical example is a
non-routed Adjacency segment bound to the End.X behavior.</t>
<t>Let N1 and N2 be two different physical nodes of the SR domain and I
a local CSID value: N1 may allocate value I to SID S1 and N2 may allocate the sa
me value I to SID S2.</t>
</section>
<section anchor="sec-csid-installation">
<name>Recommended Installation of CSIDs in FIB</name>
<t><xref target="RFC8754" sectionFormat="of" section="4.3"/> defines how
an SR segment endpoint node identifies a locally instantiated SRv6 SID. To ensu
re that any valid argument value is accepted, an SR segment endpoint node instan
tiating a NEXT-CSID or REPLACE-CSID flavor SID should install a corresponding FI
B entry that matches only the Locator and Function parts of the SID (i.e., with
a prefix length of LBL + LNL + FL).</t>
<t>In addition, an SR segment endpoint node instantiating NEXT-CSID flav
or SIDs from both the GIB and LIB may install combined "Global + Local" FIB entr
ies to match a sequence of global and local CSIDs in a single longest-prefix mat
ch (LPM) lookup.</t>
<t>For example, let us consider an SR segment endpoint node 10 instantia
ting the following two NEXT-CSID flavor SIDs according to the CSID length, Locat
or-Block length, and GIB/LIB recommendations in this section.</t>
<ul spacing="normal">
<li>
<t>The SID <tt>2001:db8:b1:10::</tt> bound to the End behavior with
the NEXT-CSID flavor is instantiated from GIB with:
</t>
<ul spacing="normal">
<li>
<t>Locator-Block length (LBL) = 48 (Locator-Block value <tt>0x20
010db800b1</tt>),</t>
</li>
<li>
<t>Locator-Node length (LNL) = 16 (Locator-Node value <tt>0x0010
</tt>),</t>
</li>
<li>
<t>Function length (FL) = 0, and</t>
</li>
<li>
<t>Argument length (AL) = 64.</t>
</li>
</ul>
</li>
<li>
<t>The SID <tt>2001:db8:b1:f123::</tt> bound to the End.X behavior f
or its local IGP adjacency <tt>123</tt> with the NEXT-CSID flavor is instantiate
d from LIB with:
</t>
<ul spacing="normal">
<li>
<t>Locator-Block length (LBL) = 48 (Locator-Block value <tt>0x20
010db800b1</tt>),</t>
</li>
<li>
<t>Locator-Node length (LNL) = 0,</t>
</li>
<li>
<t>Function length (FL) = 16 (Function value <tt>0xf123</tt>), a
nd</t>
</li>
<li>
<t>Argument length (AL) = 64.</t>
</li>
</ul>
</li>
</ul>
<t><xref target="sec-control-plane"/> discusses how the SIDs of this document an <t>For SID <tt>2001:db8:b1:10::</tt>, Node 10 would install the FIB entr
d their structure can be advertised to the SR source node through various contro y <tt>2001:db8:b1:10::/64</tt> bound to the End SID with the NEXT-CSID flavor.</
l plane protocols. The SID structure may also be learned through configuration o t>
r <t>For SID <tt>2001:db8:b1:f123::</tt>, Node 10 would install the FIB en
try <tt>2001:db8:b1:f123::/64</tt> bound to the End.X SID for adjacency <tt>123<
/tt> with the NEXT-CSID flavor.</t>
<t>In addition, Node 10 may also install the combined FIB entry <tt>2001
:db8:b1:10:f123::/80</tt> bound to the End.X SID for adjacency <tt>123</tt> with
the NEXT-CSID flavor.</t>
<t>As another example, let us consider an SR segment endpoint node 20 in
stantiating the following two REPLACE-CSID flavor SIDs according to the CSID len
gth, Locator-Block length, and GIB/LIB recommendations in this section.</t>
<ul spacing="normal">
<li>
<t><tt>2001:db8:b2:20:1::</tt> from GIB with Locator-Block length (L
BL) = 48, Locator-Node length (LNL) = 16, Function length (FL) = 16, Argument le
ngth (AL) = 48, and bound to the End behavior with the REPLACE-CSID flavor.</t>
</li>
<li>
<t><tt>2001:db8:b2:20:123::</tt> from GIB with Locator-Block length
(LBL) = 48, Locator-Node length (LNL) = 16, Function length (FL) = 16, Argument
length (AL) = 48, and bound to the End.X behavior for its local IGP adjacency <t
t>123</tt> with the REPLACE-CSID flavor.</t>
</li>
</ul>
<t>For SID <tt>2001:db8:b2:20:1::</tt>, Node 20 would install the FIB en
try <tt>2001:db8:b2:20:1::/80</tt> bound to the End SID with the REPLACE-CSID fl
avor.</t>
<t>For SID <tt>2001:db8:b2:20:123::</tt>, Node 20 would install the FIB
entry <tt>2001:db8:b2:20:123::/80</tt> bound to the End.X SID for adjacency <tt>
123</tt> with the REPLACE-CSID flavor.</t>
</section>
</section>
<section anchor="sec-source-node">
<name>SR Source Node</name>
<t>An SR source node may learn from a control plane protocol (see <xref ta
rget="sec-control-plane"/>) or local configuration the SIDs that it can use in a
segment list, along with their respective SRv6 endpoint behavior, structure, an
d any other relevant attribute (e.g., the set of L3 adjacencies associated with
an End.X SID).</t>
<section anchor="sid-validation-for-compression">
<name>SID Validation for Compression</name>
<t>As part of the compression process or as a preliminary step, the SR s
ource node <bcp14>MUST</bcp14> validate the SID structure of each SID of this do
cument in the segment list. The SR source node does so regardless of whether the
segment list is explicitly configured, locally computed, or advertised by a con
troller (e.g., via BGP <xref target="I-D.ietf-idr-sr-policy-safi"/> or PCEP <xre
f target="RFC9603"/>).</t>
<t>A SID structure is valid for compression if it meets all the followin
g conditions:</t>
<ul spacing="normal">
<li>
<t>The Locator-Block length is not 0.</t>
</li>
<li>
<t>The sum of the Locator-Node length and Function length is not 0.<
/t>
</li>
<li>
<t>The Argument length is equal to 128-LBL-LNL-FL.</t>
</li>
</ul>
<t>When compressing a SID list, the SR source node <bcp14>MUST</bcp14> t
reat an invalid SID structure as unknown. A SID with an unknown SID structure is
not compressible.</t>
<t><xref target="sec-control-plane"/> discusses how the SIDs of this doc
ument and their structure can be advertised to the SR source node through variou
s control plane protocols. The SID structure may also be learned through configu
ration or
other management protocols. The details of such mechanisms are outside the scope of this document.</t> other management protocols. The details of such mechanisms are outside the scope of this document.</t>
</section>
<section anchor="sec-source-compression">
<name>Segment List Compression</name>
<t>An SR source node <bcp14>MAY</bcp14> compress a SID list when it incl
udes NEXT-CSID and/or REPLACE-CSID flavor SIDs to reduce the packet header lengt
h.</t>
<t>It is out of the scope of this document to describe the mechanism thr
ough which an uncompressed SID list is derived, since such a mechanism may inclu
de a wide range of considerations independent of compression (e.g., minimizing a
specific metric, excluding certain links, or providing a loop-free fast-reroute
path). As general guidance for implementation or future specification, such a m
echanism should aim to select the combination of SIDs that would result in the s
hortest compressed SID list. For example, by selecting a CSID flavor SID over an
equivalent non-CSID flavor SID or by consistently selecting SIDs of the same CS
ID flavor within each routing domain.</t>
<t>The SID list that the SR source node pushes onto the packet <bcp14>MU
ST</bcp14> comply with the rules in Sections <xref target="sec-source-next" form
at="counter"/> and <xref target="sec-source-replace" format="counter"/> and expr
ess the same list of segments as the original SID list. If these rules are not f
ollowed, the packet may get dropped or misrouted.</t>
<t>If an SR source node chooses to compress the SID list, one method is
described below for illustrative purposes. Any other method producing a compress
ed SID list of equal or shorter length than the uncompressed SID list <bcp14>MAY
</bcp14> be used.</t>
<t>This method walks the uncompressed SID list and compresses each serie
s of consecutive NEXT-CSID flavor SIDs and each series of consecutive REPLACE-CS
ID flavor SIDs.</t>
<ul spacing="normal">
<li><t>When the compression method encounters a series of one or
more consecutive compressible NEXT-CSID flavor SIDs, it compresses
the series as follows. A SID with the NEXT-CSID flavor is
compressible if its structure is known to the SR source node and its
Argument value is 0.</t>
</section> <sourcecode type="pseudocode"><![CDATA[
<section anchor="sec-source-compression"><name>Segment List Compression</name>
<t>An SR source node MAY compress a SID list when it includes NEXT-CSID and/or R
EPLACE-CSID flavor SIDs to reduce the packet header length.</t>
<t>It is out of the scope of this document to describe the mechanism through whi
ch an uncompressed SID list is derived, since such mechanism may include a wide
range of considerations independent of compression (e.g., minimizing a specific
metric, excluding certain links, or providing a loop-free fast-reroute path). As
a general guidance for implementation or future specification, such a mechanism
should aim to select the combination of SIDs that would result in the shortest
compressed SID list. For example, by selecting a CSID flavor SID over an equival
ent non-CSID flavor SID or by consistently selecting SIDs of the same CSID flavo
r within each routing domain.</t>
<t>The SID list that the SR source node pushes onto the packet MUST comply with
the rules in <xref target="sec-source-next"/> and <xref target="sec-source-repla
ce"/> and express the same list of segments as the original SID list. If these r
ules are not followed, the packet may get dropped or misrouted.</t>
<t>If an SR source node chooses to compress the SID list, one method is describe
d below for illustrative purposes. Any other method producing a compressed SID l
ist of equal or shorter length than the uncompressed SID list MAY be used.</t>
<t>This method walks the uncompressed SID list and compresses each series of con
secutive NEXT-CSID flavor SIDs and each series of consecutive REPLACE-CSID flavo
r SIDs.</t>
<t><list style="symbols">
<t>When the compression method encounters a series of one or more consecutive
compressible NEXT-CSID flavor SIDs, it compresses the series as follows. A SID w
ith the NEXT-CSID flavor is compressible if its structure is known to the SR sou
rce node and its Argument value is 0.</t>
</list></t>
<figure><artwork><![CDATA[
S01. Initialize a NEXT-CSID container equal to the first SID in the S01. Initialize a NEXT-CSID container equal to the first SID in the
series, and initialize the remaining capacity of the CSID series and initialize the remaining capacity of the CSID
container to the AL of that SID container to the AL of that SID
S02. For each subsequent SID in the series { S02. For each subsequent SID in the series {
S03. If the current SID Locator-Block matches that of the CSID S03. If the current SID Locator-Block matches that of the CSID
container and the current SID LNFL is lower than or equal to container and the current SID LNFL is lower than or equal to
the remaining capacity of the NEXT-CSID container { the remaining capacity of the NEXT-CSID container {
S04. Copy the current SID Locator-Node and Function to the most S04. Copy the current SID Locator-Node and Function to the most
significant remaining Argument bits of the NEXT-CSID significant remaining Argument bits of the NEXT-CSID
container and decrement the remaining capacity by LNFL container and decrement the remaining capacity by LNFL
S05. } Else { S05. } Else {
S06. Push the NEXT-CSID container onto the compressed SID list S06. Push the NEXT-CSID container onto the compressed SID list
S07. Initialize a new NEXT-CSID container equal to the current S07. Initialize a new NEXT-CSID container equal to the current
SID in the series, and initialize the remaining capacity SID in the series and initialize the remaining capacity
of the NEXT-CSID container to the AL of that SID of the NEXT-CSID container to the AL of that SID
S08. } // End If S08. } // End If
S09. } // End For S09. } // End For
S10. If at least one SID remains in the uncompressed SID list S10. If at least one SID remains in the uncompressed SID list
(following the series of compressible NEXT-CSID flavor SIDs){ (following the series of compressible NEXT-CSID flavor SIDs){
S11. Set S to the next SID in the uncompressed SID list S11. Set S to the next SID in the uncompressed SID list
S12. If S is advertised with a SID structure, and the Locator-Block S12. If S is advertised with a SID structure, and the Locator-Block
of S matches that of the NEXT-CSID container, and the sum of of S matches that of the NEXT-CSID container, and the sum of
the Locator-Node, Function, and Argument length of S is the Locator-Node, Function, and Argument length of S is
lower than or equal to the remaining capacity of the CSID lower than or equal to the remaining capacity of the CSID
container { container {
S13. Copy the Locator-Node, Function, and Argument of S to the S13. Copy the Locator-Node, Function, and Argument of S to the
most significant remaining Argument bits of the CSID most significant remaining Argument bits of the CSID
container container
S14. } // End If S14. } // End If
S15. } // End If S15. } // End If
S16. Push the NEXT-CSID container onto the compressed SID list S16. Push the NEXT-CSID container onto the compressed SID list
]]></artwork></figure> ]]></sourcecode>
</li>
<t><list style="symbols"> <li><t>When the compression method encounters a series of
<t>When the compression method encounters a series of REPLACE-CSID flavor SIDs REPLACE-CSID flavor SIDs of the same CSID length in the uncompressed
of the same CSID length in the uncompressed SID list, it compresses the series SID list, it compresses the series as per the following high-level
as per the following high-level pseudo code. A compression checking function Com pseudo code. A compression checking function ComCheck(F, S) is
Check(F, S) is defined to check if two SIDs F and S share the same SID structure defined to check if two SIDs F and S share the same SID structure
and Locator-Block value, and if S has either no Argument or an Argument with va and Locator-Block value, and if S has either no Argument or an
lue 0. If the check passes, then ComCheck(F,S) returns true.</t> Argument with value 0. If the check passes, then ComCheck(F,S)
</list></t> returns true.</t>
<figure><artwork><![CDATA[ <sourcecode type="pseudocode"><![CDATA[
S01. Initialize a REPLACE-CSID container in full SID format equal to S01. Initialize a REPLACE-CSID container in full SID format equal to
the first SID in the series the first SID in the series
S02. Push the REPLACE-CSID container onto the compressed SID list S02. Push the REPLACE-CSID container onto the compressed SID list
S03. Initialize a new REPLACE-CSID container in packed format if S03. Initialize a new REPLACE-CSID container in packed format if
there are more than one SIDs, and initialize the remaining there are more than one SIDs and initialize the remaining
capacity of the REPLACE-CSID container to 128 bits capacity of the REPLACE-CSID container to 128 bits
S04. For each subsequent SID in the uncompressed SID list { S04. For each subsequent SID in the uncompressed SID list {
S05. Set S to the current SID in the uncompressed SID list S05. Set S to the current SID in the uncompressed SID list
S06. If ComCheck(First SID, S) { S06. If ComCheck(First SID, S) {
S07. If the LNFL of S is lower than or equal to S07. If the LNFL of S is lower than or equal to
the remaining capacity of the REPLACE-CSID container { the remaining capacity of the REPLACE-CSID container {
S08. Copy the Locator-Node and Function of S to the least S08. Copy the Locator-Node and Function of S to the least
significant remaining bits of the REPLACE-CSID container significant remaining bits of the REPLACE-CSID container
and decrement the remaining capacity by LNFL // Note and decrement the remaining capacity by LNFL // Note
S09. } Else { S09. } Else {
skipping to change at line 1232 skipping to change at line 1218
significant remaining bits of the REPLACE-CSID container significant remaining bits of the REPLACE-CSID container
and decrement the remaining capacity by LNFL // Note and decrement the remaining capacity by LNFL // Note
S13. } S13. }
S14. If S is not a REPLACE-CSID flavor SID, then break S14. If S is not a REPLACE-CSID flavor SID, then break
S15. } Else { S15. } Else {
S16. Break S16. Break
S17. } // End If S17. } // End If
S18. } // End For S18. } // End For
S19. Push the REPLACE-CSID container (if it is not empty) onto the S19. Push the REPLACE-CSID container (if it is not empty) onto the
compressed SID list compressed SID list
]]></artwork></figure> ]]></sourcecode>
</li>
<aside> </ul>
<t>Note: When the last CSID is an End.DT2M SID with the REPLACE-CSID flavor, i <aside>
f there is 0 or at least two CSID positions left in the current REPLACE-CSID con <t>Note: When the last CSID is an End.DT2M SID with the REPLACE-CSID f
tainer, the CSID is encoded as described above and the value of the Arg.FE2 argu lavor, if there are 0 or at least two CSID positions left in the current REPLACE
ment is placed in the 16 least significant bits of the next CSID position. Other -CSID container, the CSID is encoded as described above and the value of the Arg
wise (if there is only one CSID position left in the current REPLACE-CSID contai .FE2 argument is placed in the 16 least significant bits of the next CSID positi
ner), the current REPLACE-CSID container is pushed onto the SID list (the value on. Otherwise (if there is only one CSID position left in the current REPLACE-CS
of the CSID position 0 remains zero) and the End.DT2M SID with the REPLACE-CSID ID container), the current REPLACE-CSID container is pushed onto the SID list (t
flavor is encoded in full SID format with the value of the Arg.FE2 argument in t he value of the CSID position 0 remains zero) and the End.DT2M SID with the REPL
he 16 most significant bits of the SID Argument.</t> ACE-CSID flavor is encoded in full SID format with the value of the Arg.FE2 argu
</aside> ment in the 16 most significant bits of the SID Argument.</t>
</aside>
<t><list style="symbols">
<t>In all remaining cases (i.e., when the compression method encounters a SID
in the uncompressed SID list that is not handled by any of the previous subrouti
nes), it pushes this SID as is onto the compressed SID list.</t>
</list></t>
<t>Regardless of how a compressed SID list is produced, the SR source node write
s it in the IPv6 packet as described in Sections 4.1 and 4.1.1 of <xref target="
RFC8754"/>. The text is reproduced below for reference.</t>
<blockquote> <t>In all remaining cases (i.e., when the compression method encounters
<t>A source node steers a packet into an SR Policy. If the SR Policy a SID in the uncompressed SID list that is not handled by any of the previous su
broutines), it pushes this SID as is onto the compressed SID list.</t>
<t>Regardless of how a compressed SID list is produced, the SR source no
de writes it in the IPv6 packet as described in Sections <xref target="RFC8754"
sectionFormat="bare" section="4.1"/> and <xref target="RFC8754" sectionFormat="b
are" section="4.1.1"/> of <xref target="RFC8754"/>. The text is reproduced below
for reference.</t>
<!-- Quoted text is correct, but it does ignore the section break
between Sections 4.1 and 4.1.1 of [RFC8754]. -->
<blockquote>
<t>A source node steers a packet into an SR Policy. If the SR Policy
results in a Segment List containing a single segment, and there is results in a Segment List containing a single segment, and there is
no need to add information to the SRH flag or add TLV; the DA is set no need to add information to the SRH flag or add TLV; the DA is set
to the single Segment List entry, and the SRH MAY be omitted.</t> to the single Segment List entry, and the SRH <bcp14>MAY</bcp14> be omitted.</t>
<t>When needed, the SRH is created as follows:</t>
<t>When needed, the SRH is created as follows:</t> <t>The Next Header and Hdr Ext Len fields are set as specified in
<xref target="RFC8200"/>.</t>
<t>The Next Header and Hdr Ext Len fields are set as specified in <t>The Routing Type field is set to 4.</t>
<xref target="RFC8200"></xref>.</t> <t>The DA of the packet is set with the value of the first segment.</t
>
<t>The Routing Type field is set to 4.</t> <t>The first element of the SRH Segment List is the ultimate segment.
<t>The DA of the packet is set with the value of the first segment.</t>
<t>The first element of the SRH Segment List is the ultimate segment.
The second element is the penultimate segment, and so on.</t> The second element is the penultimate segment, and so on.</t>
<t>The Segments Left field is set to n-1, where n is the number of
<t>The Segments Left field is set to n-1, where n is the number of
elements in the SR Policy.</t> elements in the SR Policy.</t>
<t>The Last Entry field is set to n-1, where n is the number of
<t>The Last Entry field is set to n-1, where n is the number of
elements in the SR Policy.</t> elements in the SR Policy.</t>
<t>TLVs (including HMAC) may be set according to their specification.<
<t>TLVs (including HMAC) may be set according to their specification.</t> /t>
<t>The packet is forwarded toward the packet's Destination Address
<t>The packet is forwarded toward the packet&#39;s Destination Address
(the first segment).</t> (the first segment).</t>
<t>When a source does not require the entire SID list to be preserved
<t>When a source does not require the entire SID list to be preserved
in the SRH, a reduced SRH may be used.</t> in the SRH, a reduced SRH may be used.</t>
<t>A reduced SRH does not contain the first segment of the related SR
<t>A reduced SRH does not contain the first segment of the related SR
Policy (the first segment is the one already in the DA of the IPv6 Policy (the first segment is the one already in the DA of the IPv6
header), and the Last Entry field is set to n-2, where n is the header), and the Last Entry field is set to n-2, where n is the
number of elements in the SR Policy.</t> number of elements in the SR Policy.</t>
</blockquote> </blockquote>
</section>
</section> <section anchor="sec-source-next">
<section anchor="sec-source-next"><name>Rules for segment lists containing NEXT-
CSID flavor SIDs</name>
<t><list style="numbers" type="1">
<t>If a Destination Options header would follow an SRH with a segment list of
more than one segment compressed as a single NEXT-CSID container, the SR source
node MUST NOT omit the SRH.</t>
<t>When the last Segment List entry (index 0) in the SRH is a NEXT-CSID contai
ner representing more than one segment and the segment S preceding the first seg
ment of this NEXT-CSID container in the segment list has the PSP flavor, then th
e PSP operation is performed at the SR segment endpoint node of S. If the PSP be
havior should instead be performed at the penultimate segment along the path, th
en the SR source node MUST NOT compress the ultimate SID of the SID list into a
NEXT-CSID container.</t>
<t>If a Destination Options header would follow an SRH with a last Segment Lis
t entry being a NEXT-CSID container representing more than one segment, the SR s
ource node MUST ensure that the PSP operation is not performed before the penult
imate SR segment endpoint node along the path.</t>
<t>When the Argument of a NEXT-CSID container is not used to full capacity, th
e remaining least significant bits of that Argument MUST be set to 0.</t>
</list></t>
</section>
<section anchor="sec-source-replace"><name>Rules for segment lists containing RE
PLACE-CSID flavor SIDs</name>
<t><list style="numbers" type="1">
<t>All SIDs compressed in a REPLACE-CSID sequence MUST share the same Locator-
Block and the same compression scheme.</t>
<t>All SIDs except the last one in a CSID sequence for REPLACE-CSID MUST have
the REPLACE-CSID flavor. If the last REPLACE-CSID container is fully filled (i.e
., the last CSID is at position 0 in the REPLACE-CSID container) and the last SI
D in the CSID sequence is not the last segment in the segment list, the last SID
in the CSID sequence MUST NOT have the REPLACE-CSID flavor.</t>
<t>When a REPLACE-CSID flavor CSID is present as the last SID in a container t
hat is not the last Segment List entry (index 0) in the SRH, the next element in
the SID list MUST be a REPLACE-CSID container in packed format carrying at leas
t one CSID.</t>
</list></t>
<t>The SR source node determines the compression scheme of REPLACE-CSID flavor S
IDs as follows.</t>
<t>When receiving a SID advertisement for a REPLACE-CSID flavor SID with LNL=16, <name>Rules for Segment Lists Containing NEXT-CSID Flavor SIDs</name>
FL=0, AL=128-LBL-LNFL, and the value of the Argument is all 0, the SR source no <ol spacing="normal" type="1"><li>
de marks both the SID and its locator as using 16-bit compression. All other SID <t>If a Destination Options header would follow an SRH with a segmen
s allocated from this locator with LNL=16, FL=16, AL=128-LBL-LNFL, and the value t list of more than one segment compressed as a single NEXT-CSID container, the
of the Argument is all 0 are also marked as using 16-bit compression. When rece SR source node <bcp14>MUST NOT</bcp14> omit the SRH.</t>
iving a SID advertisement for a REPLACE-CSID flavor SID with LNFL=32, AL=128-LBL </li>
-LNFL, and the value of the Argument is all 0, the SR source node marks both the <li>
SID and its locator as using 32-bit compression.</t> <t>When the last Segment List entry (index 0) in the SRH is a NEXT-C
SID container representing more than one segment and the segment S preceding the
first segment of this NEXT-CSID container in the segment list has the PSP flavo
r, then the PSP operation is performed at the SR segment endpoint node of S. If
the PSP behavior should instead be performed at the penultimate segment along th
e path, then the SR source node <bcp14>MUST NOT</bcp14> compress the ultimate SI
D of the SID list into a NEXT-CSID container.</t>
</li>
<li>
<t>If a Destination Options header would follow an SRH with a last S
egment List entry being a NEXT-CSID container representing more than one segment
, the SR source node <bcp14>MUST</bcp14> ensure that the PSP operation is not pe
rformed before the penultimate SR segment endpoint node along the path.</t>
</li>
<li>
<t>When the Argument of a NEXT-CSID container is not used to full ca
pacity, the remaining least significant bits of that Argument <bcp14>MUST</bcp14
> be set to 0.</t>
</li>
</ol>
</section>
<section anchor="sec-source-replace">
<name>Rules for Segment Lists Containing REPLACE-CSID Flavor SIDs</name>
<ol spacing="normal" type="1"><li>
<t>All SIDs compressed in a REPLACE-CSID sequence <bcp14>MUST</bcp14
> share the same Locator-Block and the same compression scheme.</t>
</li>
<li>
<t>All SIDs except the last one in a CSID sequence for REPLACE-CSID
<bcp14>MUST</bcp14> have the REPLACE-CSID flavor. If the last REPLACE-CSID conta
iner is fully filled (i.e., the last CSID is at position 0 in the REPLACE-CSID c
ontainer) and the last SID in the CSID sequence is not the last segment in the s
egment list, the last SID in the CSID sequence <bcp14>MUST NOT</bcp14> have the
REPLACE-CSID flavor.</t>
</li>
<li>
<t>When a REPLACE-CSID flavor CSID is present as the last SID in a c
ontainer that is not the last Segment List entry (index 0) in the SRH, the next
element in the SID list <bcp14>MUST</bcp14> be a REPLACE-CSID container in packe
d format carrying at least one CSID.</t>
</li>
</ol>
<t>The SR source node determines the compression scheme of REPLACE-CSID
flavor SIDs as follows.</t>
</section> <!--[rfced] We had two questions related to this text:
<section anchor="sec-source-checksum"><name>Upper-Layer Checksums</name>
<t>The Destination Address used in the IPv6 pseudo-header (Section 8.1 of <xref a) Please review our edit to use "all zeros" instead of "all 0" in
target="RFC8200"/>) is that of the ultimate destination.</t> cases like the following and confirm this is not a meaning change.
<t>At the SR source node, that address will be the Destination Address as it is expected to be received by the ultimate destination. When the last element in th e compressed SID list is a CSID container, this address can be obtained from the last element in the uncompressed SID list or by repeatedly applying the segment behavior as described in <xref target="sec-operations-icmp-error"/>. This appli es regardless of whether an SRH is present in the IPv6 packet or omitted.</t> Original:
<t>At the ultimate destination(s), that address will be in the Destination Addre When receiving a SID advertisement for a REPLACE-CSID flavor SID with
ss field of the IPv6 header.</t> LNL=16, FL=0, AL=128-LBL-LNFL, and the value of the Argument is all
0,...
</section> Current:
</section> When receiving a SID advertisement for a REPLACE-CSID flavor SID with
<section anchor="sec-inter-domain"><name>Inter-Domain Compression</name> LNL=16, FL=0, AL=128-LBL-LNFL, and all zeros as the value of the Argument,...
<t>Some SRv6 traffic may need to cross multiple routing domains, such as differe b) May we update to add spacing around the equals sign to match
nt Autonomous Systems (ASes) or different routing areas within an SR domain. Dif previous uses (for all similar cases as well)?
ferent routing domains may use different addressing schema and Locator-Blocks.</ -->
t>
<t>A property of a CSID sequence is that all CSIDs in the sequence share the sam <t>When receiving a SID advertisement for a REPLACE-CSID flavor SID with
e Locator-Block. Therefore, a segment list that spans multiple routing domains u LNL=16, FL=0, AL=128-LBL-LNFL, and all zeros as the value of the Argument, the
sing different Locator-Blocks may need a separate CSID sequence for each domain. SR source node marks both the SID and its locator as using 16-bit compression. A
</t> ll other SIDs allocated from this locator with LNL=16, FL=16, AL=128-LBL-LNFL, a
nd all zeros as the value of the Argument are also marked as using 16-bit compre
ssion. When receiving a SID advertisement for a REPLACE-CSID flavor SID with LNF
L=32, AL=128-LBL-LNFL, and all zeros as the value of the Argument, the SR source
node marks both the SID and its locator as using 32-bit compression.</t>
</section>
<section anchor="sec-source-checksum">
<name>Upper-Layer Checksums</name>
<t>The Destination Address used in the IPv6 pseudo-header (<xref target=
"RFC8200" sectionFormat="of" section="8.1"/>) is that of the ultimate destinatio
n.</t>
<t>This section defines a solution to improve the efficiency of CSID compression <!--[rfced] Can you clarify what "that address" (used twice) and "this
in multi-domain environments by enabling a CSID sequence to combine CSIDs havin address" are referring to in Section 6?
g different Locator-Blocks.</t>
<t>The solution leverages two new SRv6 endpoint behaviors, &quot;Endpoint with S Original:
Rv6 Locator-Block Swap&quot; (&quot;End.LBS&quot; for short) and &quot;Endpoint The Destination Address used in the IPv6 pseudo-header (Section 8.1
with L3 cross-connect and SRv6 Locator-Block Swap&quot; (&quot;End.XLBS&quot; fo of [RFC8200]) is that of the ultimate destination.
r short), that enable modifying the Locator-Block for the next CSID in the CSID
sequence at the routing domain boundary.</t>
<section anchor="endlbs-locator-block-swap"><name>End.LBS: Locator-Block Swap</n At the SR source node, that address will be the Destination Address
ame> as it is expected to be received by the ultimate destination. When
the last element in the compressed SID list is a CSID container,
this address can be obtained from the last element in the
uncompressed SID list or by repeatedly applying the segment
behavior as described in Section 9.4. This applies regardless of
whether an SRH is present in the IPv6 packet or omitted.
<t>The End.LBS behavior is a variant of the End behavior that modifies the Locat At the ultimate destination(s), that address will be in the
or-Block of the active CSID sequence. This document defines the End.LBS behavior Destination Address field of the IPv6 header.
with the NEXT-CSID flavor and the End.LBS behavior with the REPLACE-CSID flavor
.</t>
<t>An End.LBS SID is used to transition to a new Locator-Block when the routing domain boundary is on the SR segment endpoint node.</t> -->
<t>Each instance of an End.LBS SID is associated with a target Locator-Block B2/ <t>At the SR source node, that address will be the Destination Address a
m, where B2 is an IPv6 address prefix and m is the associated prefix length. s it is expected to be received by the ultimate destination. When the last eleme
The original and target Locator-Blocks can have different prefix lengths as long nt in the compressed SID list is a CSID container, this address can be obtained
as the new Destination Address formed by combining the target Locator-Block wit from the last element in the uncompressed SID list or by repeatedly applying the
h the Locator-Node, Function, and Argument as described in the pseudocodes of <x segment behavior as described in <xref target="sec-operations-icmp-error"/>. Th
ref target="sec-next-endlbs"/> and <xref target="sec-replace-endlbs"/> is a vali is applies regardless of whether an SRH is present in the IPv6 packet or is omit
d IPv6 address. ted.</t>
<t>At the ultimate destination(s), that address will be in the Destinati
on Address field of the IPv6 header.</t>
</section>
</section>
<section anchor="sec-inter-domain">
<name>Inter-Domain Compression</name>
<t>Some SRv6 traffic may need to cross multiple routing domains, such as d
ifferent Autonomous Systems (ASes) or different routing areas within an SR domai
n. Different routing domains may use different addressing schema and Locator-Blo
cks.</t>
<t>A property of a CSID sequence is that all CSIDs in the sequence share t
he same Locator-Block. Therefore, a segment list that spans multiple routing dom
ains using different Locator-Blocks may need a separate CSID sequence for each d
omain.</t>
<t>This section defines a solution to improve the efficiency of CSID compr
ession in multi-domain environments by enabling a CSID sequence to combine CSIDs
having different Locator-Blocks.</t>
<t>The solution leverages two new SRv6 endpoint behaviors, "Endpoint with
SRv6 Locator-Block Swap" ("End.LBS" for short) and "Endpoint with L3 cross-conne
ct and SRv6 Locator-Block Swap" ("End.XLBS" for short), that enable modifying th
e Locator-Block for the next CSID in the CSID sequence at the routing domain bou
ndary.</t>
<section anchor="endlbs-locator-block-swap">
<name>End.LBS: Locator-Block Swap</name>
<t>The End.LBS behavior is a variant of the End behavior that modifies t
he Locator-Block of the active CSID sequence. This document defines the End.LBS
behavior with the NEXT-CSID flavor and the End.LBS behavior with the REPLACE-CSI
D flavor.</t>
<t>An End.LBS SID is used to transition to a new Locator-Block when the
routing domain boundary is on the SR segment endpoint node.</t>
<t>Each instance of an End.LBS SID is associated with a target Locator-B
lock B2/m, where B2 is an IPv6 address prefix and m is the associated prefix len
gth.
The original and target Locator-Blocks can have different prefix lengths as long
as the new Destination Address formed by combining the target Locator-Block wit
h the Locator-Node, Function, and Argument as described in the pseudocode of Sec
tions <xref target="sec-next-endlbs" format="counter"/> and <xref target="sec-re
place-endlbs" format="counter"/> is a valid IPv6 address.
The target Locator-Block is a local property of the End.LBS SID on the SR segmen t endpoint node.</t> The target Locator-Block is a local property of the End.LBS SID on the SR segmen t endpoint node.</t>
<aside> <!-- [rfced] The following may require clarification:
<t>Note: a local SID property is an attribute associated with the SID when it
is instantiated on the SR segment endpoint node. When the SR segment endpoint no
de identifies the destination address of a received packet as a locally instanti
ated SID, it also retrieves any local property associated with this SID. Other e
xamples of local SID properties include the set of L3 adjacencies of an End.X SI
D (Section 4.2 of <xref target="RFC8986"/>) and the lookup table of an End.DT6 S
ID (Section 4.6 of <xref target="RFC8986"/>).</t>
</aside>
<t>The means by which an SR source node learns the target Locator-Block associat
ed with an End.LBS SID are outside the scope of this document. As examples, it c
ould be learned via configuration or signaled by a controller.</t>
<section anchor="sec-next-endlbs"><name>End.LBS with NEXT-CSID</name> Current:
| Other examples of local SID properties include the set of L3
| adjacencies of an End.X SID (Section 4.1 of [RFC8986]) and the
| lookup table of an End.DT6 SID (Section 4.6 of [RFC8986]).
<t>When processing an IPv6 packet that matches a FIB entry locally instantiated We note that Section 4.1 of [RFC8986] is titled "End: Endpoint" while
as an End.LBS SID with the NEXT-CSID flavor and associated with the target Locat Section 4.2 of [RFC8986] is titled "End.X: L3 Cross-Connect". Section
or-Block B2/m, the SR segment endpoint node applies the procedure specified in < 4.2 may be the more appropriate section to reference in this case.
xref target="sec-next-end"/> with the lines N05 to N06 replaced as follows.</t> Please advise.
<figure><artwork><![CDATA[ -->
<aside>
<t>Note: a local SID property is an attribute associated with the SID
when it is instantiated on the SR segment endpoint node. When the SR segment end
point node identifies the destination address of a received packet as a locally
instantiated SID, it also retrieves any local property associated with this SID.
Other examples of local SID properties include the set of L3 adjacencies of an
End.X SID (<xref target="RFC8986" sectionFormat="of" section="4.1"/>) and the lo
okup table of an End.DT6 SID (<xref target="RFC8986" sectionFormat="of" section=
"4.6"/>).</t>
</aside>
<t>The means by which an SR source node learns the target Locator-Block
associated with an End.LBS SID are outside the scope of this document. As exampl
es, it could be learned via configuration or signaled by a controller.</t>
<section anchor="sec-next-endlbs">
<name>End.LBS with NEXT-CSID</name>
<t>When processing an IPv6 packet that matches a FIB entry locally ins
tantiated as an End.LBS SID with the NEXT-CSID flavor and associated with the ta
rget Locator-Block B2/m, the SR segment endpoint node applies the procedure spec
ified in <xref target="sec-next-end"/> with the lines N05 to N06 replaced as fol
lows.</t>
<sourcecode type="pseudocode"><![CDATA[
N05.1. Initialize an IPv6 address A equal to B2. N05.1. Initialize an IPv6 address A equal to B2.
N05.2. Copy DA.Argument into the bits [m..(m+AL-1)] of A. N05.2. Copy DA.Argument into the bits [m..(m+AL-1)] of A.
N06. Copy A to the Destination Address of the IPv6 header. N06. Copy A to the Destination Address of the IPv6 header.
]]></artwork></figure> ]]></sourcecode>
</section>
</section> <section anchor="sec-replace-endlbs">
<section anchor="sec-replace-endlbs"><name>End.LBS with REPLACE-CSID</name> <name>End.LBS with REPLACE-CSID</name>
<t>When processing an IPv6 packet that matches a FIB entry locally ins
<t>When processing an IPv6 packet that matches a FIB entry locally instantiated tantiated as an End.LBS SID with the REPLACE-CSID flavor and associated with the
as an End.LBS SID with the REPLACE-CSID flavor and associated with the target Lo target Locator-Block B2/m, the SR segment endpoint node applies the procedure s
cator-Block B2/m, the SR segment endpoint node applies the procedure specified i pecified in <xref target="sec-replace-end"/> with the line R20 replaced as follo
n <xref target="sec-replace-end"/> with the line R20 replaced as follows.</t> ws.</t>
<sourcecode type="pseudocode"><![CDATA[
<figure><artwork><![CDATA[
R20.1. Initialize an IPv6 address A equal to B2. R20.1. Initialize an IPv6 address A equal to B2.
R20.2. Write Segment List[Segments Left][DA.Arg.Index] into the bits R20.2. Write Segment List[Segments Left][DA.Arg.Index] into the bits
[m..m+LNFL-1] of A. [m..m+LNFL-1] of A.
R20.3. Write DA.Arg.Index into the bits R20.3. Write DA.Arg.Index into the bits
[(128-ceiling(log_2(128/LNFL)))..127] of A. [(128-ceiling(log_2(128/LNFL)))..127] of A.
R20.4. Copy A to the Destination Address of the IPv6 header. R20.4. Copy A to the Destination Address of the IPv6 header.
]]></artwork></figure> ]]></sourcecode>
</section>
</section> </section>
</section> <section anchor="endxlbs-l3-cross-connect-and-locator-block-swap">
<section anchor="endxlbs-l3-cross-connect-and-locator-block-swap"><name>End.XLBS <name>End.XLBS: L3 Cross-Connect and Locator-Block Swap</name>
: L3 Cross-Connect and Locator-Block Swap</name> <t>The End.XLBS behavior is a variant of the End.X behavior that modifie
s the Locator-Block of the active CSID sequence. This document defines the End.X
<t>The End.XLBS behavior is a variant of the End.X behavior that modifies the Lo LBS behavior with the NEXT-CSID flavor and the End.XLBS behavior with the REPLAC
cator-Block of the active CSID sequence. This document defines the End.XLBS beha E-CSID flavor.</t>
vior with the NEXT-CSID flavor and the End.XLBS behavior with the REPLACE-CSID f <t>An End.XLBS SID is used to transition to a new Locator-Block when the
lavor.</t> routing domain boundary is on a link adjacent to the SR segment endpoint node.<
/t>
<t>An End.XLBS SID is used to transition to a new Locator-Block when the routing <t>Each instance of an End.XLBS SID is associated with a target Locator-
domain boundary is on a link adjacent to the SR segment endpoint node.</t> Block B2/m and a set, J, of one or more L3 adjacencies.
The original and target Locator-Blocks can have different prefix lengths as long
<t>Each instance of an End.XLBS SID is associated with a target Locator-Block B2 as the new Destination Address formed by combining the target Locator-Block wit
/m and a set, J, of one or more L3 adjacencies. h the Locator-Node, Function, and Argument as described in the pseudocode of Sec
The original and target Locator-Blocks can have different prefix lengths as long tions <xref target="sec-next-endxlbs" format="counter"/> and <xref target="sec-r
as the new Destination Address formed by combining the target Locator-Block wit eplace-endxlbs" format="counter" /> is a valid IPv6 address.
h the Locator-Node, Function, and Argument as described in the pseudocodes of <x
ref target="sec-next-endxlbs"/> and <xref target="sec-replace-endxlbs"/> is a va
lid IPv6 address.
The target Locator-Block and set of adjacencies are local properties of the End. XLBS SID on the SR segment endpoint node.</t> The target Locator-Block and set of adjacencies are local properties of the End. XLBS SID on the SR segment endpoint node.</t>
<t>The means by which an SR source node learns the target Locator-Block
<t>The means by which an SR source node learns the target Locator-Block associat associated with an End.XLBS SID are outside the scope of this document. As examp
ed with an End.XLBS SID are outside the scope of this document. As examples, it les, it could be learned via configuration or signaled by a controller.</t>
could be learned via configuration or signaled by a controller.</t> <section anchor="sec-next-endxlbs">
<name>End.XLBS with NEXT-CSID</name>
<section anchor="sec-next-endxlbs"><name>End.XLBS with NEXT-CSID</name> <t>When processing an IPv6 packet that matches a FIB entry locally ins
tantiated as an End.XLBS SID with the NEXT-CSID flavor and associated with the t
<t>When processing an IPv6 packet that matches a FIB entry locally instantiated arget Locator-Block B2/m, the SR segment endpoint node applies the procedure spe
as an End.XLBS SID with the NEXT-CSID flavor and associated with the target Loca cified in <xref target="sec-next-endx"/> with the lines N05 to N06 (of the pseud
tor-Block B2/m, the SR segment endpoint node applies the procedure specified in ocode in <xref target="sec-next-end"/>) replaced as follows.</t>
<xref target="sec-next-endx"/> with the lines N05 to N06 (of the pseudocode in < <sourcecode type="pseudocode"><![CDATA[
xref target="sec-next-end"/>) replaced as follows.</t>
<figure><artwork><![CDATA[
N05.1. Initialize an IPv6 address A equal to B2. N05.1. Initialize an IPv6 address A equal to B2.
N05.2. Copy DA.Argument into the bits [m..(m+AL-1)] of A. N05.2. Copy DA.Argument into the bits [m..(m+AL-1)] of A.
N06. Copy A to the Destination Address of the IPv6 header. N06. Copy A to the Destination Address of the IPv6 header.
]]></artwork></figure> ]]></sourcecode>
</section>
</section> <section anchor="sec-replace-endxlbs">
<section anchor="sec-replace-endxlbs"><name>End.XLBS with REPLACE-CSID</name> <name>End.XLBS with REPLACE-CSID</name>
<t>When processing an IPv6 packet that matches a FIB entry locally ins
<t>When processing an IPv6 packet that matches a FIB entry locally instantiated tantiated as an End.XLBS SID with the REPLACE-CSID flavor and associated with th
as an End.XLBS SID with the REPLACE-CSID flavor and associated with the target L e target Locator-Block B2/m, the SR segment endpoint node applies the procedure
ocator-Block B2/m, the SR segment endpoint node applies the procedure specified specified in <xref target="sec-replace-endx"/> with the line R20 (of the pseudoc
in <xref target="sec-replace-endx"/> with the line R20 (of the pseudocode in <xr ode in <xref target="sec-replace-end"/>) replaced as follows.</t>
ef target="sec-replace-end"/>) replaced as follows.</t> <sourcecode type="pseudocode"><![CDATA[
<figure><artwork><![CDATA[
R20.1. Initialize an IPv6 address A equal to B2. R20.1. Initialize an IPv6 address A equal to B2.
R20.2. Write Segment List[Segments Left][DA.Arg.Index] into the bits R20.2. Write Segment List[Segments Left][DA.Arg.Index] into the bits
[m..m+LNFL-1] of A. [m..m+LNFL-1] of A.
R20.3. Write DA.Arg.Index into the bits R20.3. Write DA.Arg.Index into the bits
[(128-ceiling(log_2(128/LNFL)))..127] of A. [(128-ceiling(log_2(128/LNFL)))..127] of A.
R20.4. Copy A to the Destination Address of the IPv6 header. R20.4. Copy A to the Destination Address of the IPv6 header.
]]></artwork></figure> ]]></sourcecode>
</section>
</section> </section>
</section> </section>
</section> <section anchor="sec-control-plane">
<section anchor="sec-control-plane"><name>Control Plane</name> <name>Control Plane</name>
<t><xref target="RFC8986" sectionFormat="of" section="8"/> provides an ove
<t>Section 8 of <xref target="RFC8986"/> provides an overview of the control pla rview of the control plane protocols used for signaling of the SRv6 endpoint beh
ne protocols used for signaling of the SRv6 endpoint behaviors introduced by tha aviors introduced by that document, including the base SRv6 endpoint behaviors t
t document, including the base SRv6 endpoint behaviors that are extended in the hat are extended in the present document.</t>
present document.</t> <t>The CSID-flavored behaviors introduced by this document are advertised
in the same manner as their base SRv6 endpoint behaviors using the SRv6 extensio
<t>The CSID-flavored behaviors introduced by this document are advertised in the ns for various routing protocols, such as:</t>
same manner as their base SRv6 endpoint behaviors using the SRv6 extensions for <ul spacing="normal">
various routing protocols, such as</t> <li>
<t>IS-IS <xref target="RFC9352"/></t>
<t><list style="symbols"> </li>
<t>IS-IS <xref target="RFC9352"/></t> <li>
<t>OSPFv3 <xref target="RFC9513"/></t> <t>OSPFv3 <xref target="RFC9513"/></t>
<t>BGP <xref target="RFC9252"/>, <xref target="RFC9514"/>, <xref target="I-D.i </li>
etf-idr-sr-policy-safi"/></t> <li>
<t>BGP-LS <xref target="I-D.ietf-idr-bgp-ls-sr-policy"/></t> <t>BGP <xref target="RFC9252"/>, <xref target="RFC9514"/>, <xref targe
<t>PCEP <xref target="RFC9603"/></t> t="I-D.ietf-idr-sr-policy-safi"/></t>
</list></t> </li>
<li>
<t>The SR segment endpoint node MUST set the SID Argument bits to 0 when adverti <t>BGP-LS <xref target="I-D.ietf-idr-bgp-ls-sr-policy"/></t>
sing a locally instantiated SID of this document in the routing protocol (e.g., </li>
IS-IS <xref target="RFC9352"/>, OSPF <xref target="RFC9513"/>, or BGP-LS <xref t <li>
arget="RFC9514"/>).</t> <t>PCEP <xref target="RFC9603"/></t>
</li>
<t>Signaling the SRv6 SID Structure is REQUIRED for all the SIDs introduced in t </ul>
his document. It is used by an SR source node to compress a SID list as describe
d in <xref target="sec-source-node"/>.
The node initiating the SID advertisement MUST set the length values in the SRv6
SID Structure to match the format of the SID on the SR segment endpoint node. F
or example, for a SID of this document instantiated from a /48 SRv6 SID block an
d a /64 Locator, and having a 16-bit Function, the SRv6 SID Structure advertisem
ent carries the following values.</t>
<t><list style="symbols">
<t>Locator-Block length: 48</t>
<t>Locator-Node length: 16</t>
<t>Function length: 16</t>
<t>Argument length: 48 (= 128-48-16-16)</t>
</list></t>
<t>A local CSID may be advertised in the control plane individually and/or in co
mbination with a global CSID instantiated on the same SR segment endpoint node,
with the End behavior, and the same Locator-Block and flavor as the local CSID.
A combined global and local CSID is advertised as follows.</t>
<t><list style="symbols">
<t>The SID Locator-Block is that shared by the global and local CSIDs</t>
<t>The SID Locator-Node is that of global CSID</t>
<t>The SID Function is that of the local CSID</t>
<t>The SID Argument length is equal to 128-LBL-LNL-FL and the SID Argument val
ue is 0</t>
<t>All other attributes of the SID (e.g., SRv6 endpoint behavior or algorithm)
are those of the local CSID</t>
</list></t>
<t>The local CSID combined advertisement is needed in particular for control pla
ne protocols mandating that the SID is a subnet of a locator advertised in the s
ame protocol (e.g., Section 8 of <xref target="RFC9352"/> and Section 9 of <xref
target="RFC9513"/> for advertising Adjacency SIDs in IS-IS and OSPFv3, respecti
vely).</t>
<t>For a segment list computed by a controller and signaled to an SR source node
(e.g., via BGP <xref target="I-D.ietf-idr-sr-policy-safi"/> or PCEP <xref targe
t="RFC9603"/>), the controller provides the ordered segment list comprising the
uncompressed SIDs, with their respective behavior and structure, to the SR sourc
e node. The SR source node may then compress the SID list as described in <xref
target="sec-source-node"/>.</t>
<t>When a node that does not support this specification receives an advertisemen
t of a SID of this document, it handles it as described in the corresponding con
trol plane specification (e.g., Sections 7.2, 8.1, and 8.2 of <xref target="RFC9
352"/>, Sections 8, 9.1, and 9.2 of <xref target="RFC9513"/>, and Section 3.1 of
<xref target="RFC9252"/>).</t>
</section>
<section anchor="operational-considerations"><name>Operational Considerations</n
ame>
<section anchor="flavor-block-and-csid-length"><name>Flavor, Block, and CSID Len
gth</name>
<t>SRv6 is intended for use in a variety of networks that require different pref
ix lengths and SID numbering spaces. Each of the two flavors introduced in this
document comes with its own recommendations for Locator-Block and CSID length, a
s specified in <xref target="sec-next"/> and <xref target="sec-replace"/>. These
flavors are best suited for different environments, depending on the requiremen
ts of the network. For instance, larger CSID lengths may be more suitable for ne
tworks requiring ample SID numbering space, while smaller CSID lengths are bette
r for compression efficiency. The two compression flavors allow the compressed s
egment list encoding to adapt to a range of requirements, with support for multi
ple compression levels. Network operators can choose the flavor that best suits
their use case, deployment design, and network scale.</t>
<t>Both CSID flavors can coexist in the same SR domain, on the same SR segment e
ndpoint node, and even in the same segment list. However, operators should gener
ally avoid instantiating SIDs of different CSID flavors within the same routing
domain or Locator-Block since these SIDs have different length and allocation re
commendations (see <xref target="sec-next"/>, <xref target="sec-replace"/>, and
<xref target="sec-csid-lib-recommendation"/>). In a multi-domain deployment, dif
ferent flavors may be used in different routing domains of the SR domain.</t>
<t>A deployment should use consistent Locator-Block lengths and CSID lengths for
all SIDs within a routing domain. Heterogeneous lengths, while possible, may im
pact the compression efficiency.</t>
<t>The compressed segment list encoding works with various Locator-Block allocat
ions. For example, each routing domain within the SR domain can be allocated a /
48 Locator-Block from a global IPv6 block available to the operator, or from a p
refix allocated to SRv6 SIDs as discussed in Section 5 of <xref target="RFC9602"
/>.</t>
</section>
<section anchor="sec-csid-lib-recommendation"><name>GIB/LIB Usage</name>
<t>GIB and LIB usage is a local implementation and/or configuration decision, ho
wever, some guidelines for determining usage for specific SRv6 endpoint behavior
s and recommendations are provided.</t>
<t>The GIB number space is shared among all SR segment endpoint nodes using SRv6
locators under a Locator-Block space. The more SIDs assigned from this space,
per node, the faster it is exhausted. Therefore, its use is prioritized for glo
bal segments, such as SIDs that identify a node.</t>
<t>The LIB number space is unique per node. Each node can fully utilize the enti
re LIB number space without consideration of assignments at other nodes. Theref
ore, its use is prioritized for local segments, such as SIDs that identify servi
ces (of which there may be many) at nodes, cross-connects, or adjacencies.</t>
<t>While a longer CSID length permits more flexibility in which SRv6 endpoint be
haviors may be assigned from the GIB; it also reduces the compression efficiency
.</t>
<t>Given the previous Locator-Block and CSID length recommendations, the followi
ng GIB/LIB usage is recommended:</t>
<t><list style="symbols">
<t>NEXT-CSID:
<list style="symbols">
<t>GIB: End</t>
<t>LIB: End.X, End.T, End.DT4/6/46/2U/2M, End.DX4/6/2/2V (including large-
scale pseudowire), End.B6.Encaps, End.B6.Encaps.Red, End.BM, End.LBS, and End.XL
BS</t>
</list></t>
<t>REPLACE-CSID:
<list style="symbols">
<t>GIB: End, End.X, End.T, End.DT4/6/46/2U/2M, End.DX4/6/2/2V, End.B6.Enca
ps, End.B6.Encaps.Red, End.BM, End.LBS, and End.XLBS</t>
<t>LIB: End.DX2/2V for large-scale pseudowire</t>
</list></t>
</list></t>
<t>Any other allocation is possible but may lead to a suboptimal use of the CSID
numbering space.</t>
</section> <t>The SR segment endpoint node <bcp14>MUST</bcp14> set the SID Argument b
<section anchor="pinging-a-sid"><name>Pinging a SID</name> its to 0 when advertising a locally instantiated SID of this document in the rou
ting protocol (e.g., IS-IS <xref target="RFC9352"/>, OSPF <xref target="RFC9513"
/>, or BGP-LS <xref target="RFC9514"/>).</t>
<t>Signaling the SRv6 SID Structure is <bcp14>REQUIRED</bcp14> for all the
SIDs introduced in this document. It is used by an SR source node to compress a
SID list as described in <xref target="sec-source-node"/>.
The node initiating the SID advertisement <bcp14>MUST</bcp14> set the length val
ues in the SRv6 SID Structure to match the format of the SID on the SR segment e
ndpoint node. For example, for a SID of this document instantiated from a /48 SR
v6 SID block and a /64 Locator, and having a 16-bit Function, the SRv6 SID Struc
ture advertisement carries the following values.</t>
<ul spacing="normal">
<li>
<t>Locator-Block length: 48</t>
</li>
<li>
<t>Locator-Node length: 16</t>
</li>
<li>
<t>Function length: 16</t>
</li>
<li>
<t>Argument length: 48 (= 128-48-16-16)</t>
</li>
</ul>
<t>A local CSID may be advertised in the control plane individually and/or
in combination with a global CSID instantiated on the same SR segment endpoint
node, with the End behavior, and the same Locator-Block and flavor as the local
CSID. A combined global and local CSID is advertised as follows:</t>
<ul spacing="normal">
<li>
<t>The SID Locator-Block is that shared by the global and local CSIDs<
/t>
</li>
<li>
<t>The SID Locator-Node is that of global CSID</t>
</li>
<li>
<t>The SID Function is that of the local CSID</t>
</li>
<li>
<t>The SID Argument length is equal to 128-LBL-LNL-FL and the SID Argu
ment value is 0</t>
</li>
<li>
<t>All other attributes of the SID (e.g., SRv6 endpoint behavior or al
gorithm) are those of the local CSID</t>
</li>
</ul>
<t>The local CSID-combined advertisement is needed in particular for contr
ol plane protocols mandating that the SID is a subnet of a locator advertised in
the same protocol (e.g., <xref target="RFC9352" sectionFormat="of" section="8"/
> and <xref target="RFC9513" sectionFormat="of" section="9"/> for advertising Ad
jacency SIDs in IS-IS and OSPFv3, respectively).</t>
<t>For a segment list computed by a controller and signaled to an SR sourc
e node (e.g., via BGP <xref target="I-D.ietf-idr-sr-policy-safi"/> or PCEP <xref
target="RFC9603"/>), the controller provides the ordered segment list comprisin
g the uncompressed SIDs, with their respective behavior and structure, to the SR
source node. The SR source node may then compress the SID list as described in
<xref target="sec-source-node"/>.</t>
<t>An SR source node may ping an SRv6 SID by sending an ICMPv6 echo request pack <!--[rfced] Would it be helpful to the reader to clarify what part of
et destined to the SRv6 SID. The SR source node may ping the target SID with a S the specification the node does not support (rather than the
ID list comprising only that target SID, or with a longer one that comprises two document itself)?
or more SIDs. In that case, the target SID is the last element in the SID list.
This operation is illustrated in Appendix A.1.2 of <xref target="RFC9259"/>.</t
>
<t>When pinging a SID of this document the SR source node MUST construct the IPv Original:
6 packet as described in <xref target="sec-source-node"/>, including computing t When a node that does not support this specification receives an
he ICMPv6 checksum as described in <xref target="sec-source-checksum"/>.</t> advertisement of a SID of this document, it handles it as described
in the corresponding control plane specification (e.g., Sections 7.2,
8.1, and 8.2 of [RFC9352], Sections 8, 9.1, and 9.2 of [RFC9513], and
Section 3.1 of [RFC9252]).
-->
<t>In particular, when pinging a SID of this document with a SID list comprising <t>When a node that does not support this specification receives an advert
only the target SID, the SR source node places the SID with Argument value 0 in isement of a SID of this document, it handles it as described in the correspondi
the destination address of the ICMPv6 echo request and computes the ICMPv6 chec ng control plane specification (e.g., Sections <xref target="RFC9352" sectionFor
ksum using this SID as the destination address in the IPv6 pseudo-header. The Ar mat="bare" section="7.2"/>, <xref target="RFC9352" sectionFormat="bare" section=
gument value 0 allows the SID SR segment endpoint node (<xref target="sec-endpoi "8.1"/>, and <xref target="RFC9352" sectionFormat="bare" section="8.2"/> of <xre
nt"/>) to identify itself as the ultimate destination of the packet and process f target="RFC9352"/>, Sections <xref target="RFC9513" sectionFormat="bare" secti
the ICMPv6 payload. on="8"/>, <xref target="RFC9513" sectionFormat="bare" section="9.1"/>, and <xref
target="RFC9513" sectionFormat="bare" section="9.2"/> of <xref target="RFC9513"
/>, and <xref target="RFC9252" sectionFormat="of" section="3.1"/>).</t>
</section>
<section anchor="operational-considerations">
<name>Operational Considerations</name>
<section anchor="flavor-block-and-csid-length">
<name>Flavor, Block, and CSID Length</name>
<t>SRv6 is intended for use in a variety of networks that require differ
ent prefix lengths and SID numbering spaces. Each of the two flavors introduced
in this document comes with its own recommendations for Locator-Block and CSID l
ength, as specified in Sections <xref target="sec-next" format="counter"/> and <
xref target="sec-replace" format="counter"/>. These flavors are best suited for
different environments, depending on the requirements of the network. For instan
ce, larger CSID lengths may be more suitable for networks requiring ample SID nu
mbering space, while smaller CSID lengths are better for compression efficiency.
The two compression flavors allow the compressed segment list encoding to adapt
to a range of requirements, with support for multiple compression levels. Netwo
rk operators can choose the flavor that best suits their use case, deployment de
sign, and network scale.</t>
<t>Both CSID flavors can coexist in the same SR domain, on the same SR s
egment endpoint node, and even in the same segment list. However, operators shou
ld generally avoid instantiating SIDs of different CSID flavors within the same
routing domain or Locator-Block since these SIDs have different length and alloc
ation recommendations (see Sections <xref target="sec-next" format="counter"/>,
<xref target="sec-replace" format="counter"/>, and <xref target="sec-csid-lib-re
commendation" format="counter"/>). In a multi-domain deployment, different flavo
rs may be used in different routing domains of the SR domain.</t>
<t>A deployment should use consistent Locator-Block lengths and CSID len
gths for all SIDs within a routing domain. Heterogeneous lengths, while possible
, may impact the compression efficiency.</t>
<t>The compressed segment list encoding works with various Locator-Block
allocations. For example, each routing domain within the SR domain can be alloc
ated a /48 Locator-Block from a global IPv6 block available to the operator or f
rom a prefix allocated to SRv6 SIDs as discussed in <xref target="RFC9602" secti
onFormat="of" section="5"/>.</t>
</section>
<section anchor="sec-csid-lib-recommendation">
<name>GIB/LIB Usage</name>
<t>GIB and LIB usage is a local implementation and/or configuration deci
sion; however, some guidelines for determining usage for specific SRv6 endpoint
behaviors and recommendations are provided.</t>
<t>The GIB number space is shared among all SR segment endpoint nodes us
ing SRv6 locators under a Locator-Block space. The more SIDs assigned from this
space, per node, the faster it is exhausted. Therefore, its use is prioritized
for global segments, such as SIDs that identify a node.</t>
<t>The LIB number space is unique per node. Each node can fully utilize
the entire LIB number space without consideration for assignments at other nodes
. Therefore, its use is prioritized for local segments, such as SIDs that ident
ify services (of which there may be many) at nodes, cross-connects, or adjacenci
es.</t>
<t>While a longer CSID length permits more flexibility in which SRv6 end
point behaviors may be assigned from the GIB, it also reduces the compression ef
ficiency.</t>
<t>Given the previous Locator-Block and CSID length recommendations, the
following GIB/LIB usage is recommended:</t>
<ul spacing="normal">
<li>
<t>NEXT-CSID:
</t>
<ul spacing="normal">
<li>
<t>GIB: End</t>
</li>
<li>
<t>LIB: End.X, End.T, End.DT4/6/46/2U/2M, End.DX4/6/2/2V (includ
ing large-scale pseudowire), End.B6.Encaps, End.B6.Encaps.Red, End.BM, End.LBS,
and End.XLBS</t>
</li>
</ul>
</li>
<li>
<t>REPLACE-CSID:
</t>
<ul spacing="normal">
<li>
<t>GIB: End, End.X, End.T, End.DT4/6/46/2U/2M, End.DX4/6/2/2V, E
nd.B6.Encaps, End.B6.Encaps.Red, End.BM, End.LBS, and End.XLBS</t>
</li>
<li>
<t>LIB: End.DX2/2V for large-scale pseudowire</t>
</li>
</ul>
</li>
</ul>
<t>Any other allocation is possible but may lead to a suboptimal use of
the CSID numbering space.</t>
</section>
<section anchor="pinging-a-sid">
<name>Pinging a SID</name>
<t>An SR source node may ping an SRv6 SID by sending an ICMPv6 echo requ
est packet destined to the SRv6 SID. The SR source node may ping the target SID
with a SID list comprising only that target SID or with a longer one that compri
ses two or more SIDs. In that case, the target SID is the last element in the SI
D list. This operation is illustrated in <xref section="A.1.2" target="RFC9259"/
>.</t>
<t>When pinging a SID of this document, the SR source node <bcp14>MUST</
bcp14> construct the IPv6 packet as described in <xref target="sec-source-node"/
>, including computing the ICMPv6 checksum as described in <xref target="sec-sou
rce-checksum"/>.</t>
<t>In particular, when pinging a SID of this document with a SID list co
mprising only the target SID, the SR source node places the SID with Argument va
lue 0 in the destination address of the ICMPv6 echo request and computes the ICM
Pv6 checksum using this SID as the destination address in the IPv6 pseudo-header
. The Argument value 0 allows the SID SR segment endpoint node (<xref target="se
c-endpoint"/>) to identify itself as the ultimate destination of the packet and
process the ICMPv6 payload.
Therefore, any existing IPv6 ping implementation can originate ICMP echo request s to a NEXT-CSID or REPLACE-CSID flavor SID with a SID list comprising only the target SID, provided that the user ensures that the SID Argument is 0.</t> Therefore, any existing IPv6 ping implementation can originate ICMP echo request s to a NEXT-CSID or REPLACE-CSID flavor SID with a SID list comprising only the target SID, provided that the user ensures that the SID Argument is 0.</t>
</section>
<section anchor="sec-operations-icmp-error">
<name>ICMP Error Processing</name>
<t>When an IPv6 node encounters an error while processing a packet, it m
ay report that error by sending an IPv6 error message to the packet source with
an enclosed copy of the invoking packet. For the source of an invoking packet to
process the ICMP error message, the ultimate destination address of the IPv6 he
ader may be required.</t>
<t><xref target="RFC8754" sectionFormat="of" section="5.4"/> defines the
logic that an SR source node follows to determine the ultimate destination of a
n invoking packet containing an SRH.</t>
<t>For an SR source node that supports the compressed segment list encod
ing defined in this document, the logic to determine the ultimate destination is
generalized as follows.</t>
<ul spacing="normal">
<li>
<t>If the destination address of the invoking IPv6 packet matches a
known SRv6 SID, modify the invoking IPv6 packet by applying the SRv6 endpoint be
havior associated with the matched SRv6 SID;</t>
</li>
<li>
<t>Repeat until the application of the SRv6 endpoint behavior would
result in the processing of the upper-layer header.</t>
</li>
</ul>
<t>The destination address of the resulting IPv6 packet may be used as t
he ultimate destination of the invoking IPv6 packet.</t>
<t>Since the SR source node that needs to determine the ultimate destina
tion is the same node that originally built the SID list in the invoking packet,
it can perform this operation for all the SIDs in the packet.</t>
</section>
</section>
</section> <section anchor="sec-future">
<section anchor="sec-operations-icmp-error"><name>ICMP Error Processing</name> <name>Applicability to Other SRv6 Endpoint Behaviors</name>
<t>Future documents may extend the applicability of the NEXT-CSID and REPL
<t>When an IPv6 node encounters an error while processing a packet, it may repor ACE-CSID flavors to other SRv6 endpoint behaviors.</t>
t that error by sending an IPv6 error message to the packet source with an enclo <t>For an SRv6 endpoint behavior that can be used before the last position
sed copy of the invoking packet. For the source of an invoking packet to process of a segment list, a CSID flavor is defined by reproducing the same logic as de
the ICMP error message, the ultimate destination address of the IPv6 header may scribed in Sections <xref target="sec-next" format="counter"/> and <xref target=
be required.</t> "sec-replace" format="counter"/> to determine the next SID in the SID list.</t>
</section>
<t>Section 5.4 of <xref target="RFC8754"/> defines the logic that an SR source n <section anchor="security-considerations">
ode follows to determine the ultimate destination of an invoking packet containi <name>Security Considerations</name>
ng an SRH.</t> <t><xref target="RFC8402" sectionFormat="of" section="8"/> discusses the s
ecurity considerations for Segment Routing.</t>
<t>For an SR source node that supports the compressed segment list encoding defi <t><xref target="RFC8754" sectionFormat="of" section="5"/> describes the i
ned in this document, the logic to determine the ultimate destination is general ntra-SR-domain deployment model and how to secure it. <xref target="RFC8754" sec
ized as follows.</t> tionFormat="of" section="7"/> describes the threats applicable to SRv6 and how t
o mitigate them.</t>
<t><list style="symbols"> <t><xref target="RFC8986" sectionFormat="of" section="9"/> discusses the s
<t>If the destination address of the invoking IPv6 packet matches a known SRv6 ecurity considerations applicable to the SRv6 network programming framework, as
SID, modify the invoking IPv6 packet by applying the SRv6 endpoint behavior ass well as the SR source node and SR segment endpoint node behaviors that it define
ociated with the matched SRv6 SID;</t> s.</t>
<t>Repeat until the application of the SRv6 endpoint behavior would result in
the processing of the upper-layer header.</t>
</list></t>
<t>The destination address of the resulting IPv6 packet may be used as the ultim
ate destination of the invoking IPv6 packet.</t>
<t>Since the SR source node that needs to determine the ultimate destination is
the same node that originally built the SID list in the invoking packet, it can
perform this operation for all the SIDs in the packet.</t>
</section>
</section>
<section removeInRFC="true" anchor="implementation-status"><name>Implementation
Status</name>
<t>RFC-Editor: Please clean up the references cited by this section before publi
cation.</t>
<t>This section records the status of known implementations of the
protocol defined by this specification at the time of posting of
this Internet-Draft, and is based on a proposal described in
<xref target="RFC7942"/>. The description of implementations in this section is
intended to assist the IETF in its decision processes in
progressing drafts to RFCs. Please note that the listing of any
individual implementation here does not imply endorsement by the
IETF. Furthermore, no effort has been spent to verify the
information presented here that was supplied by IETF contributors.
This is not intended as, and must not be construed to be, a
catalog of available implementations or their features. Readers
are advised to note that other implementations may exist.</t>
<t>According to <xref target="RFC7942"/>, &quot;this will allow reviewers and wo
rking
groups to assign due consideration to documents that have the
benefit of running code, which may serve as evidence of valuable
experimentation and feedback that have made the implemented
protocols more mature. It is up to the individual working groups
to use this information as they see fit&quot;.</t>
<t>This section is provided in compliance with the SPRING working group policies
(<xref target="SPRING-WG-POLICIES"/>).</t>
<section anchor="cisco-systems"><name>Cisco Systems</name>
<t>Cisco Systems reported the following implementations of the SR segment endpoi
nt node NEXT-CSID flavor (<xref target="sec-next"/>) and the SR source node effi
cient SID list encoding (<xref target="sec-source-node"/>) for NEXT-CSID flavor
SIDs. These are used as part of its SRv6 TI-LFA, micro-loop avoidance, and traff
ic engineering functionalities.</t>
<t><list style="symbols">
<t>Cisco NCS 540 Series routers running IOS XR 7.3.x or above <xref target="IM
PL-CISCO-NCS540"/></t>
<t>Cisco NCS 560 Series routers running IOS XR 7.6.x or above <xref target="IM
PL-CISCO-NCS560"/></t>
<t>Cisco NCS 5500 Series routers running IOS XR 7.3.x or above <xref target="I
MPL-CISCO-NCS5500"/></t>
<t>Cisco NCS 5700 Series routers running IOS XR 7.5.x or above <xref target="I
MPL-CISCO-NCS5700"/></t>
<t>Cisco 8000 Series routers running IOS XR 7.5.x or above <xref target="IMPL-
CISCO-8000"/></t>
<t>Cisco ASR 9000 Series routers running IOS XR 7.5.x or above <xref target="I
MPL-CISCO-ASR9000"/></t>
</list></t>
<t>At the time of this report, all the implementations listed above are in produ
ction and follow the specification in the latest version of this document, inclu
ding all the &quot;MUST&quot; and &quot;SHOULD&quot; clauses for the NEXT-CSID f
lavor.</t>
<t>This report was last updated on January 11, 2023.</t>
</section>
<section anchor="huawei-technologies"><name>Huawei Technologies</name>
<t>Huawei Technologies reported the following implementations of the SR segment
endpoint node REPLACE-CSID flavor (<xref target="sec-replace"/>).
These are used as part of its SRv6 TI-LFA, micro-loop avoidance, and traffic eng
ineering functionalities.</t>
<t><list style="symbols">
<t>Huawei ATN8XX,ATN910C,ATN980B routers running VRPV800R021C00 or above.</t>
<t>Huawei CX600-M2 routers running VRPV800R021C00 or above.</t>
<t>Huawei NE40E,ME60-X1X2,ME60-X3X8X16 routers running VRPV800R021C00 or above
.</t>
<t>Huawei NE5000E,NE9000 routers running VRPV800R021C00 or above.</t>
<t>Huawei NCE-IP Controller running V1R21C00 or above.</t>
</list></t>
<t>At the time of this report, all the implementations listed above are in produ
ction and follow the specification in the latest version of this document, inclu
ding all the &quot;MUST&quot; and &quot;SHOULD&quot; clauses for the REPLACE-CSI
D flavor.</t>
<t>This report was last updated on January 11, 2023.</t>
</section>
<section anchor="nokia"><name>Nokia</name>
<t>Nokia reported the following implementations (<xref target="IMPL-NOKIA-20.10"
/>) of the SR segment endpoint node NEXT-CSID flavor (<xref target="sec-next"/>)
. These are used as part of its shortest path forwarding (in algorithm 0 and Fl
ex-Algo), remote and TI-LFA repair tunnel, and Traffic Engineering functionaliti
es.</t>
<t><list style="symbols">
<t>Nokia 7950 XRS 20/20e routers running SROS Release 22.10 or above</t>
<t>Nokia 7750 SR-12e routers running SROS Release 22.10 or above</t>
<t>Nokia 7750 SR-7/12 routers running SROS Release 22.10 or above</t>
<t>Nokia 7750 SR-7s/14s routers running SROS Release 22.10 or above</t>
<t>Nokia 7750 SR-1/1s/2s routers running SROS Release 22.10 or above</t>
</list></t>
<t>At the time of this report, all the implementations listed above are in produ
ction and follow the specification in the latest version of this document, inclu
ding all the &quot;MUST&quot; and &quot;SHOULD&quot; clauses for the NEXT-CSID f
lavor.</t>
<t>This report was last updated on February 3, 2023.</t>
</section>
<section anchor="arrcus"><name>Arrcus</name>
<t>Arrcus reported the following implementations of the SR segment endpoint node
NEXT-CSID flavor (<xref target="sec-next"/>). These are used as part of its SRv
6 shortest path forwarding (in algorithm 0 and Flex-Algo), TI-LFA, micro-loop a
voidance and Traffic Engineering functionalities.</t>
<t><list style="symbols">
<t>Arrcus running on Ufi Space routers S9510-28DC, S9710-76D, S9600-30DX and S
9700-23D with ArcOS v5.2.1 or above</t>
<t>Arrcus running n Ufi Space routers S9600-72XC and S9700-53DX with ArcOS v5.
1.1D or above</t>
<t>Arrcus running on Quanta router IXA and IXAE with ArcOS v5.1.1D or above</t
>
</list></t>
<t>At the time of this report, all the implementations listed above are in produ
ction and follow the specification in the latest version of this document, inclu
ding all the &quot;MUST&quot; and &quot;SHOULD&quot; clauses for the NEXT-CSID f
lavor.</t>
<t>This report was last updated on March 11, 2023.</t>
</section>
<section anchor="juniper-networks"><name>Juniper Networks</name>
<t>Juniper Networks reported the following implementations of the SR segment end
point node NEXT-CSID flavor (<xref target="sec-next"/>). These are used as part
of its SRv6 shortest path forwarding (in algorithm 0 and Flex-Algo), TI-LFA, mic
ro-loop avoidance, and Traffic Engineering functionalities.</t>
<t>Juniper release 23.3 onwards supports this functionality.</t>
<t>At the time of this report, all the implementations listed above are in devel
opment and follow the specification in the latest version of this document, incl
uding all the &quot;MUST&quot; and &quot;SHOULD&quot; clauses for the NEXT-CSID
flavor.</t>
<t>This report was last updated on May 30, 2023.</t>
</section>
<section anchor="marvell"><name>Marvell</name>
<t>Marvell reported support in the Marvell Prestera Packet Processor for the SR
segment endpoint node NEXT-CSID flavor (<xref target="sec-next"/>) and REPLACE-C
SID flavor (<xref target="sec-replace"/>).</t>
<t>This report was last updated on February 15, 2023.</t>
</section>
<section anchor="broadcom"><name>Broadcom</name>
<t>Broadcom reported the following implementations of the SR segment endpoint no
de NEXT-CSID flavor (<xref target="sec-next"/>) and REPLACE-CSID flavor (<xref t
arget="sec-replace"/>). These are used as part of its SRv6 TI-LFA, micro-loop a
voidance, and traffic engineering functionalities. All implementation of the fol
lowing list is in general availability for customers using BCM SDK 6.5.26 or abo
ve.</t>
<t><list style="symbols">
<t>88850 (Jericho2c+) series</t>
<t>88690 (Jericho2) series</t>
<t>88800 (Jericho2c) series</t>
<t>88480 (Qunran2a) series</t>
<t>88280 (Qunran2u) series</t>
<t>88295 (Qunran2n) series</t>
<t>88830 (Jericho2x) series</t>
</list></t>
<t>At the time of this report, all the implementations listed above are in produ
ction and follow the specification in the latest version of this document, inclu
ding all the &quot;MUST&quot; and &quot;SHOULD&quot; clauses for the NEXT-CSID a
nd REPLACE-CSID flavors.</t>
<t>For 78900 (Tomahawk) series-related support, please contact the Broadcom team
.</t>
<t>This report was last updated on February 21, 2023.</t>
</section>
<section anchor="zte-corporation"><name>ZTE Corporation</name>
<t>ZTE Corporation reported the following implementations of the SR segment endp
oint node REPLACE-CSID flavor (<xref target="sec-replace"/>). These are used as
part of its SRv6 TI-LFA, micro-loop avoidance, and traffic engineering functiona
lities.</t>
<t><list style="symbols">
<t>ZTE M6000-18S(BRAS), M6000-8S Plus(BRAS) routers running V5.00.10.09 or abo
ve.</t>
<t>ZTE M6000-18S(SR), M6000-8S Plus(SR) routers running V5.00.10.80 or above.<
/t>
<t>ZTE T8000-18 routers running V5.00.10.07 or above.</t>
</list></t>
<t>This report was last updated on March 29, 2023.</t>
</section>
<section anchor="new-h3c-technologies"><name>New H3C Technologies</name>
<t>New H3C Technologies reported the following implementations of the SR segment
endpoint node REPLACE-CSID flavor (<xref target="sec-replace"/>). These are use
d as part of its SRv6 TI-LFA, micro-loop avoidance, and traffic engineering func
tionalities.</t>
<t><list style="symbols">
<t>H3C CR16000-F, SR8800-X routers running Version 7.1.075 or above.</t>
<t>H3C CR18000, CR19000 routers running Version 7.1.071 or above.</t>
</list></t>
<t>This report was last updated on March 29, 2023.</t>
</section>
<section anchor="ruijie-network"><name>Ruijie Network</name>
<t>Ruijie Network reported the following implementations of the SR segment endpo
int node REPLACE-CSID flavor (<xref target="sec-replace"/>). These are used as p
art of its SRv6 TI-LFA, micro-loop avoidance, and traffic engineering functional
ities.</t>
<t><list style="symbols">
<t>RUIJIE RG-N8018-R, RG-N8010-R routers running N8000-R_RGOS 12.8(3)B0801 or
above.</t>
</list></t>
<t>This report was last updated on March 29, 2023.</t>
</section>
<section anchor="ciena"><name>Ciena</name>
<t>Ciena reported the following implementations of the SR segment endpoint node
NEXT-CSID flavor (<xref target="sec-next"/>). These are used as part of its shor
test path forwarding (in algorithm 0 and Flex-Algo), remote and TI-LFA repair tu
nnel, and Traffic Engineering functionalities.</t>
<t>The following platforms support implementation of the above.</t>
<t><list style="symbols">
<t>Ciena 5162, 5164, 5166, 5168 routers running SAOS 10.10 or above</t>
<t>Ciena 8110, 8112, 8190 routers running SAOS 10.10 or above</t>
</list></t>
<t>At the time of this report, all the implementations listed above are in produ
ction and follow the specification in the latest version of this document, inclu
ding all the &quot;MUST&quot; and &quot;SHOULD&quot; clauses for the NEXT-CSID f
lavor.</t>
<t>This report was last updated on February 6, 2024.</t>
</section>
<section anchor="centec"><name>Centec</name>
<t>Centec reported the following implementations of the SR segment endpoint node
REPLACE-CSID flavor (<xref target="sec-replace"/>). These are used as part of i
ts SRv6 TI-LFA, micro-loop avoidance, and traffic engineering functionalities. A
ll implementation of the following list is in general availability for customers
using Centec SDK 5.6.8 or above.</t>
<t><list style="symbols">
<t>CTC7132 (TsingMa) Series</t>
<t>CTC8180 (TsingMa.MX) Series</t>
</list></t>
<t>This report was last updated on February 14, 2024.</t>
</section>
<section anchor="open-source"><name>Open-Source</name>
<t>The authors found the following open-source implementations of the SR segment
endpoint node NEXT-CSID flavor (<xref target="sec-next"/>).</t>
<t><list style="symbols">
<t>The Linux kernel, version 6.1 <xref target="IMPL-OSS-LINUX"/></t>
<t>The Software for Open Networking in the Cloud (SONiC), version 202212 <xref
target="IMPL-OSS-SONIC"/>, and Switch Abstraction Interface (SAI), version 1.9
.0 <xref target="IMPL-OSS-SAI"/></t>
<t>The Vector Packet Processor (VPP), version 20.05 <xref target="IMPL-OSS-VPP
"/></t>
<t>A generic P4 implementation <xref target="IMPL-OSS-P4"/></t>
</list></t>
<t>The authors found the following open-source implementations of the SR segment
endpoint node REPLACE-CSID flavor (<xref target="sec-replace"/>).</t>
<t><list style="symbols">
<t>ONOS and P4 Programmable Switch based <xref target="IMPL-OSS-ONOS"/></t>
<t>Open SRv6 Project <xref target="IMPL-OSS-OPEN-SRV6"/></t>
</list></t>
<t>This section was last updated on January 11, 2023.</t>
</section>
<section anchor="interoperability-reports"><name>Interoperability Reports</name>
<section anchor="eantc-2024"><name>EANTC 2024</name>
<t>In April 2024, the European Advanced Networking Test Center (EANTC) successfu
lly validated multiple implementations of SRv6 NEXT-CSID flavor (a.k.a., SRv6 uS
ID) <xref target="EANTC-24"/>.</t>
<t>The participating vendors included Arista, Ciena, Cisco, Ericsson, H3C, Huawe
i, Juniper, Keysight, Nokia, and ZTE.</t>
</section>
<section anchor="bell-canada-ciena-2023"><name>Bell Canada / Ciena 2023</name>
<t>Bell Canada is currently evaluating interoperability between Ciena and Cisco
implementations of the NEXT-CSID flavor defined in this document. Further inform
ation will be added to this section when the evaluation is complete.</t>
</section>
<section anchor="eantc-2023"><name>EANTC 2023</name>
<t>In April 2023, the European Advanced Networking Test Center (EANTC) successfu
lly validated multiple implementations of SRv6 NEXT-CSID flavor (a.k.a., SRv6 uS
ID) <xref target="EANTC-23"/>.</t>
<t>The participating vendors included Arista, Arrcus, Cisco, Huawei, Juniper, Ke
ysight, Nokia, and Spirent.</t>
</section>
<section anchor="china-mobile-2020"><name>China Mobile 2020</name>
<t>In November 2020, China Mobile successfully validated multiple interoperable
implementations of the NEXT-CSID and REPLACE-CSID flavors defined in this docume
nt.</t>
<t>This testing covered two different implementations of the SRv6 endpoint flavo
rs defined in this document:</t>
<t><list style="symbols">
<t>Hardware implementation in Cisco ASR 9000 running IOS XR</t>
<t>Software implementation in Cisco IOS XRv9000 virtual appliance</t>
<t>Hardware implementation in Huawei NE40E and NE5000E running VRP</t>
</list></t>
<t>The interoperability testing consisted of a packet flow sent by an SR source
node N0 via an SR traffic engineering policy with a segment list <spanx style="v
erb">&lt;S1, S2, S3, S4, S5, S6, S7&gt;</spanx>, where S1..S7 are SIDs instantia
ted on SR segment endpoint nodes N1..N7, respectively.</t>
<figure><artset><artwork type="svg"><svg xmlns="http://www.w3.org/2000/svg" ver
sion="1.1" height="64" width="424" viewBox="0 0 424 64" class="diagram" text-anc
hor="middle" font-family="monospace" font-size="13px" stroke-linecap="round">
<path d="M 32,32 L 48,32" fill="none" stroke="black"/>
<path d="M 88,32 L 104,32" fill="none" stroke="black"/>
<path d="M 144,32 L 160,32" fill="none" stroke="black"/>
<path d="M 200,32 L 216,32" fill="none" stroke="black"/>
<path d="M 256,32 L 272,32" fill="none" stroke="black"/>
<path d="M 312,32 L 328,32" fill="none" stroke="black"/>
<path d="M 368,32 L 384,32" fill="none" stroke="black"/>
<g class="text">
<text x="12" y="36">N0</text>
<text x="68" y="36">N1</text>
<text x="124" y="36">N2</text>
<text x="180" y="36">N3</text>
<text x="236" y="36">N4</text>
<text x="292" y="36">N5</text>
<text x="348" y="36">N6</text>
<text x="404" y="36">N7</text>
<text x="68" y="52">(S1)</text>
<text x="124" y="52">(S2)</text>
<text x="180" y="52">(S3)</text>
<text x="236" y="52">(S4)</text>
<text x="292" y="52">(S5)</text>
<text x="348" y="52">(S6)</text>
<text x="404" y="52">(S7)</text>
</g>
</svg>
</artwork><artwork type="ascii-art"><![CDATA[
N0 --- N1 --- N2 --- N3 --- N4 --- N5 --- N6 --- N7
(S1) (S2) (S3) (S4) (S5) (S6) (S7)
]]></artwork></artset></figure>
<t><list style="symbols">
<t>N0 is a generic packet generator.</t>
<t>N1, N2, and N3 are Huawei routers.</t>
<t>N4, N5, and N6 are Cisco routers.</t>
<t>N7 is a generic traffic generator acting as a packet receiver.</t>
</list></t>
<t>The SR source node N0 steers the packets onto the SR policy by setting the IP
v6 destination address and creating an SRH (as described in Section 4.1 of <xref
target="RFC8754"/>) using a compressed segment list encoding. The length of the
compressed segment list encoding varies for each scenario.</t>
<t>All SR segment endpoint nodes execute a variant of the End behavior: regular
End behavior (as defined in Section 4.1 of <xref target="RFC8986"/>), End behavi
or with NEXT-CSID flavor, and End behavior with REPLACE-CSID flavor. The variant
being used at each SR segment endpoint node varies for each scenario.</t>
<t>The interoperability was validated for the following scenarios:</t>
<t><strong>Scenario 1:</strong></t>
<t><list style="symbols">
<t>S1 and S2 are associated with the End behavior with the REPLACE-CSID flavor
</t>
<t>S3 is associated with the regular End behavior (no flavor)</t>
<t>S4, S5, and S6 are associated with the End behavior with the NEXT-CSID flav
or</t>
<t>The SR source node imposes a compressed segment list encoding of 3 SIDs.</t
>
</list></t>
<t><strong>Scenario 2:</strong></t>
<t><list style="symbols">
<t>S1, S2..., S6 are associated with the End behavior with the NEXT-CSID flavo
r</t>
<t>The SR source node imposes a compressed segment list encoding of 2 SIDs.</t
>
</list></t>
<t><strong>Scenario 3:</strong></t>
<t><list style="symbols">
<t>S1, S2..., S6 are associated with the End behavior with the REPLACE-CSID fl
avor</t>
<t>The SR source node imposes a compressed segment list encoding of 3 SIDs.</t
>
</list></t>
</section>
</section>
</section>
<section anchor="sec-future"><name>Applicability to other SRv6 Endpoint Behavior
s</name>
<t>Future documents may extend the applicability of the NEXT-CSID and REPLACE-CS
ID flavors to other SRv6 endpoint behaviors.</t>
<t>For an SRv6 endpoint behavior that can be used before the last position of a
segment list, a CSID flavor is defined by reproducing the same logic as describe
d in <xref target="sec-next"/> and <xref target="sec-replace"/> of this document
to determine the next SID in the SID list.</t>
</section>
<section anchor="security-considerations"><name>Security Considerations</name>
<t>Section 8 of <xref target="RFC8402"/> discusses the security considerations f
or Segment Routing.</t>
<t>Section 5 of <xref target="RFC8754"/> describes the intra-SR-domain deploymen
t model and how to secure it. Section 7 of <xref target="RFC8754"/> describes th
e threats applicable to SRv6 and how to mitigate them.</t>
<t>Section 9 of <xref target="RFC8986"/> discusses the security considerations a
pplicable to the SRv6 network programming framework, as well as the SR source no
de and SR segment endpoint node behaviors that it defines.</t>
<t>This document introduces two new flavors for some of the SRv6 endpoint behavi
ors defined in <xref target="RFC8986"/> and a method by which an SR source node
may leverage the SIDs of these flavors to produce a compressed segment list enco
ding.</t>
<t>This document also introduces two new SRv6 endpoint behaviors, End.LBS and En
d.XLBS, to preserve the efficiency of CSID compression in multi-domain environme
nts.</t>
<t>An SR source node constructs an IPv6 packet with a compressed segment list en
coding as defined in Sections 3.1 and 4.1 of <xref target="RFC8754"/> and Sectio
n 5 of <xref target="RFC8986"/>. The paths that an SR source node may enforce us
ing a compressed segment list encoding are the same, from a topology and service
perspective, as those that an SR source node could enforce using the SIDs of <x
ref target="RFC8986"/>.</t>
<t>An SR segment endpoint node processes an IPv6 packet matching a locally insta
ntiated SID as defined in <xref target="RFC8986"/>, with the pseudocode modifica
tions in Section 4 of this document. These modifications change how the SR segme
nt endpoint node determines the next SID in the packet, but not the semantic of
either the active or the next SID. For example, an adjacency segment instantiate
d with the End.X behavior remains an adjacency segment regardless of whether it
uses the base End.X behavior defined in Section 4.2 of <xref target="RFC8986"/>
or a CSID flavor of that behavior. This document does not introduce any new SID
semantic.</t>
<t>Any other transit node processes the packet as described in Section 4.2 of <x
ref target="RFC8754"/>.</t>
<t>This document defines a new method of encoding the SIDs inside a SID list at
the SR source node (<xref target="sec-source-node"/>) and decoding them at the S
R segment endpoint node (<xref target="sec-endpoint"/> and <xref target="sec-int
er-domain"/>), but it does not change how the SID list itself is encoded in the
IPv6 packet nor the semantic of any segment that it comprises. Therefore, this d
ocument is subject to the same security considerations that are discussed in <xr
ef target="RFC8402"/>, <xref target="RFC8754"/>, and <xref target="RFC8986"/>.</
t>
</section>
<section anchor="iana-considerations"><name>IANA Considerations</name>
<section anchor="srv6-endpoint-behaviors"><name>SRv6 Endpoint Behaviors</name>
<t>This I-D. requests the IANA to update the reference of the following registra
tions from the &quot;SRv6 Endpoint Behaviors&quot; registry under the top-level
&quot;Segment Routing&quot; registry-group (https://www.iana.org/assignments/seg
ment-routing/) with the RFC number of this document once it is published, and tr
ansfer change control to the IETF.</t>
<texttable title="Registration List" anchor="tbl-iana-endpoint-behaviors">
<ttcol align='left'>Value</ttcol>
<ttcol align='left'>Description</ttcol>
<ttcol align='left'>Reference</ttcol>
<c>43</c>
<c>End with NEXT-CSID</c>
<c>This I-D.</c>
<c>44</c>
<c>End with NEXT-CSID &amp; PSP</c>
<c>This I-D.</c>
<c>45</c>
<c>End with NEXT-CSID &amp; USP</c>
<c>This I-D.</c>
<c>46</c>
<c>End with NEXT-CSID, PSP &amp; USP</c>
<c>This I-D.</c>
<c>47</c>
<c>End with NEXT-CSID &amp; USD</c>
<c>This I-D.</c>
<c>48</c>
<c>End with NEXT-CSID, PSP &amp; USD</c>
<c>This I-D.</c>
<c>49</c>
<c>End with NEXT-CSID, USP &amp; USD</c>
<c>This I-D.</c>
<c>50</c>
<c>End with NEXT-CSID, PSP, USP &amp; USD</c>
<c>This I-D.</c>
<c>52</c>
<c>End.X with NEXT-CSID</c>
<c>This I-D.</c>
<c>53</c>
<c>End.X with NEXT-CSID &amp; PSP</c>
<c>This I-D.</c>
<c>54</c>
<c>End.X with NEXT-CSID &amp; USP</c>
<c>This I-D.</c>
<c>55</c>
<c>End.X with NEXT-CSID, PSP &amp; USP</c>
<c>This I-D.</c>
<c>56</c>
<c>End.X with NEXT-CSID &amp; USD</c>
<c>This I-D.</c>
<c>57</c>
<c>End.X with NEXT-CSID, PSP &amp; USD</c>
<c>This I-D.</c>
<c>58</c>
<c>End.X with NEXT-CSID, USP &amp; USD</c>
<c>This I-D.</c>
<c>59</c>
<c>End.X with NEXT-CSID, PSP, USP &amp; USD</c>
<c>This I-D.</c>
<c>85</c>
<c>End.T with NEXT-CSID</c>
<c>This I-D.</c>
<c>86</c>
<c>End.T with NEXT-CSID &amp; PSP</c>
<c>This I-D.</c>
<c>87</c>
<c>End.T with NEXT-CSID &amp; USP</c>
<c>This I-D.</c>
<c>88</c>
<c>End.T with NEXT-CSID, PSP &amp; USP</c>
<c>This I-D.</c>
<c>89</c>
<c>End.T with NEXT-CSID &amp; USD</c>
<c>This I-D.</c>
<c>90</c>
<c>End.T with NEXT-CSID, PSP &amp; USD</c>
<c>This I-D.</c>
<c>91</c>
<c>End.T with NEXT-CSID, USP &amp; USD</c>
<c>This I-D.</c>
<c>92</c>
<c>End.T with NEXT-CSID, PSP, USP &amp; USD</c>
<c>This I-D.</c>
<c>93</c>
<c>End.B6.Encaps with NEXT-CSID</c>
<c>This I-D.</c>
<c>94</c>
<c>End.B6.Encaps.Red with NEXT-CSID</c>
<c>This I-D.</c>
<c>95</c>
<c>End.BM with NEXT-CSID</c>
<c>This I-D.</c>
<c>96</c>
<c>End.LBS with NEXT-CSID</c>
<c>This I-D.</c>
<c>97</c>
<c>End.XLBS with NEXT-CSID</c>
<c>This I-D.</c>
<c>101</c>
<c>End with REPLACE-CSID</c>
<c>This I-D.</c>
<c>102</c>
<c>End with REPLACE-CSID &amp; PSP</c>
<c>This I-D.</c>
<c>103</c>
<c>End with REPLACE-CSID &amp; USP</c>
<c>This I-D.</c>
<c>104</c>
<c>End with REPLACE-CSID, PSP &amp; USP</c>
<c>This I-D.</c>
<c>105</c>
<c>End.X with REPLACE-CSID</c>
<c>This I-D.</c>
<c>106</c>
<c>End.X with REPLACE-CSID &amp; PSP</c>
<c>This I-D.</c>
<c>107</c>
<c>End.X with REPLACE-CSID &amp; USP</c>
<c>This I-D.</c>
<c>108</c>
<c>End.X with REPLACE-CSID, PSP &amp; USP</c>
<c>This I-D.</c>
<c>109</c>
<c>End.T with REPLACE-CSID</c>
<c>This I-D.</c>
<c>110</c>
<c>End.T with REPLACE-CSID &amp; PSP</c>
<c>This I-D.</c>
<c>111</c>
<c>End.T with REPLACE-CSID &amp; USP</c>
<c>This I-D.</c>
<c>112</c>
<c>End.T with REPLACE-CSID, PSP &amp; USP</c>
<c>This I-D.</c>
<c>114</c>
<c>End.B6.Encaps with REPLACE-CSID</c>
<c>This I-D.</c>
<c>115</c>
<c>End.BM with REPLACE-CSID</c>
<c>This I-D.</c>
<c>116</c>
<c>End.DX6 with REPLACE-CSID</c>
<c>This I-D.</c>
<c>117</c>
<c>End.DX4 with REPLACE-CSID</c>
<c>This I-D.</c>
<c>118</c>
<c>End.DT6 with REPLACE-CSID</c>
<c>This I-D.</c>
<c>119</c>
<c>End.DT4 with REPLACE-CSID</c>
<c>This I-D.</c>
<c>120</c>
<c>End.DT46 with REPLACE-CSID</c>
<c>This I-D.</c>
<c>121</c>
<c>End.DX2 with REPLACE-CSID</c>
<c>This I-D.</c>
<c>122</c>
<c>End.DX2V with REPLACE-CSID</c>
<c>This I-D.</c>
<c>123</c>
<c>End.DT2U with REPLACE-CSID</c>
<c>This I-D.</c>
<c>124</c>
<c>End.DT2M with REPLACE-CSID</c>
<c>This I-D.</c>
<c>127</c>
<c>End.B6.Encaps.Red with REPLACE-CSID</c>
<c>This I-D.</c>
<c>128</c>
<c>End with REPLACE-CSID &amp; USD</c>
<c>This I-D.</c>
<c>129</c>
<c>End with REPLACE-CSID, PSP &amp; USD</c>
<c>This I-D.</c>
<c>130</c>
<c>End with REPLACE-CSID, USP &amp; USD</c>
<c>This I-D.</c>
<c>131</c>
<c>End with REPLACE-CSID, PSP, USP &amp; USD</c>
<c>This I-D.</c>
<c>132</c>
<c>End.X with REPLACE-CSID &amp; USD</c>
<c>This I-D.</c>
<c>133</c>
<c>End.X with REPLACE-CSID, PSP &amp; USD</c>
<c>This I-D.</c>
<c>134</c>
<c>End.X with REPLACE-CSID, USP &amp; USD</c>
<c>This I-D.</c>
<c>135</c>
<c>End.X with REPLACE-CSID, PSP, USP &amp; USD</c>
<c>This I-D.</c>
<c>136</c>
<c>End.T with REPLACE-CSID &amp; USD</c>
<c>This I-D.</c>
<c>137</c>
<c>End.T with REPLACE-CSID, PSP &amp; USD</c>
<c>This I-D.</c>
<c>138</c>
<c>End.T with REPLACE-CSID, USP &amp; USD</c>
<c>This I-D.</c>
<c>139</c>
<c>End.T with REPLACE-CSID, PSP, USP &amp; USD</c>
<c>This I-D.</c>
<c>140</c>
<c>End.LBS with REPLACE-CSID</c>
<c>This I-D.</c>
<c>141</c>
<c>End.XLBS with REPLACE-CSID</c>
<c>This I-D.</c>
</texttable>
</section>
</section>
<section anchor="acknowledgements"><name>Acknowledgements</name>
<t>The authors would like to thank Kamran Raza, Xing Jiang, YuanChao Su, Han Li, <!--[rfced] Please review our update to this text to try to make it
Yisong Liu, Martin Vigoureux, Joel Halpern, and Tal Mizrahi for their insightfu more parallel to the paragraph that follows.
l feedback and suggestions.</t>
<t>The authors would also like to thank Andrew Alston, Linda Dunbar, Adrian Farr Original:
el, Boris Hassanov, Alvaro Retana, and Gunter Van de Velde for their thorough re This document introduces two new flavors for some of the SRv6 endpoint
view of this document.</t> behaviors defined in [RFC8986] and a method by which an SR source node
may leverage the SIDs of these flavors to produce a compressed segment
list encoding.
</section> Current:
This document introduces two new flavors, NEXT-CSID and REPLACE-CSID, for some o
f the SRv6 endpoint behaviors defined in RFC 8986 and a method by which an SR so
urce node may leverage the SIDs of these flavors to produce a compressed segment
list encoding.
-->
<t>This document introduces two new flavors, NEXT-CSID and REPLACE-CSID, f
or some of the SRv6 endpoint behaviors defined in <xref target="RFC8986"/> and a
method by which an SR source node may leverage the SIDs of these flavors to pro
duce a compressed segment list encoding.</t>
<t>This document also introduces two new SRv6 endpoint behaviors, End.LBS
and End.XLBS, to preserve the efficiency of CSID compression in multi-domain env
ironments.</t>
<t>An SR source node constructs an IPv6 packet with a compressed segment l
ist encoding as defined in Sections <xref target="RFC8754" sectionFormat="bare"
section="3.1"/> and <xref target="RFC8754" sectionFormat="bare" section="4.1"/>
of <xref target="RFC8754"/> and <xref target="RFC8986" sectionFormat="of" sectio
n="5"/>. The paths that an SR source node may enforce using a compressed segment
list encoding are the same, from a topology and service perspective, as those t
hat an SR source node could enforce using the SIDs of <xref target="RFC8986"/>.<
/t>
<t>An SR segment endpoint node processes an IPv6 packet matching a locally
instantiated SID as defined in <xref target="RFC8986"/>, with the pseudocode mo
difications in <xref target="sec-endpoint"/> of this document. These modificatio
ns change how the SR segment endpoint node determines the next SID in the packet
but not the semantic of either the active or the next SID. For example, an adja
cency segment instantiated with the End.X behavior remains an adjacency segment
regardless of whether it uses the base End.X behavior defined in <xref target="R
FC8986" sectionFormat="of" section="4.2"/> or a CSID flavor of that behavior. Th
is document does not introduce any new SID semantic.</t>
<t>Any other transit node processes the packet as described in <xref targe
t="RFC8754" sectionFormat="of" section="4.2"/>.</t>
<t>This document defines a new method of encoding the SIDs inside a SID li
st at the SR source node (<xref target="sec-source-node"/>) and decoding them at
the SR segment endpoint node (see Sections <xref target="sec-endpoint" format="
counter"/> and <xref target="sec-inter-domain" format="counter"/>), but it does
not change how the SID list itself is encoded in the IPv6 packet nor the semanti
c of any segment that it comprises. Therefore, this document is subject to the s
ame security considerations that are discussed in <xref target="RFC8402"/>, <xre
f target="RFC8754"/>, and <xref target="RFC8986"/>.</t>
</section>
<section anchor="iana-considerations">
<name>IANA Considerations</name>
<section anchor="srv6-endpoint-behaviors">
<name>SRv6 Endpoint Behaviors</name>
<t>IANA has updated the reference of the following registrations from th
e "SRv6 Endpoint Behaviors" registry under the "Segment Routing" registry group
(<eref brackets="angle" target="https://www.iana.org/assignments/segment-routing
/"/>) to point to this document and transfer change control to the IETF.</t>
<table anchor="tbl-iana-endpoint-behaviors">
<name>SRv6 Endpoint Behaviors Registration List</name>
<thead>
<tr>
<th align="left">Value</th>
<th align="left">Description</th>
<th align="left">Reference</th>
</tr>
</thead>
<tbody>
<tr>
<td align="left">43</td>
<td align="left">End with NEXT-CSID</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">44</td>
<td align="left">End with NEXT-CSID &amp; PSP</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">45</td>
<td align="left">End with NEXT-CSID &amp; USP</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">46</td>
<td align="left">End with NEXT-CSID, PSP &amp; USP</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">47</td>
<td align="left">End with NEXT-CSID &amp; USD</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">48</td>
<td align="left">End with NEXT-CSID, PSP &amp; USD</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">49</td>
<td align="left">End with NEXT-CSID, USP &amp; USD</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">50</td>
<td align="left">End with NEXT-CSID, PSP, USP &amp; USD</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">52</td>
<td align="left">End.X with NEXT-CSID</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">53</td>
<td align="left">End.X with NEXT-CSID &amp; PSP</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">54</td>
<td align="left">End.X with NEXT-CSID &amp; USP</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">55</td>
<td align="left">End.X with NEXT-CSID, PSP &amp; USP</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">56</td>
<td align="left">End.X with NEXT-CSID &amp; USD</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">57</td>
<td align="left">End.X with NEXT-CSID, PSP &amp; USD</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">58</td>
<td align="left">End.X with NEXT-CSID, USP &amp; USD</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">59</td>
<td align="left">End.X with NEXT-CSID, PSP, USP &amp; USD</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">85</td>
<td align="left">End.T with NEXT-CSID</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">86</td>
<td align="left">End.T with NEXT-CSID &amp; PSP</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">87</td>
<td align="left">End.T with NEXT-CSID &amp; USP</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">88</td>
<td align="left">End.T with NEXT-CSID, PSP &amp; USP</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">89</td>
<td align="left">End.T with NEXT-CSID &amp; USD</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">90</td>
<td align="left">End.T with NEXT-CSID, PSP &amp; USD</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">91</td>
<td align="left">End.T with NEXT-CSID, USP &amp; USD</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">92</td>
<td align="left">End.T with NEXT-CSID, PSP, USP &amp; USD</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">93</td>
<td align="left">End.B6.Encaps with NEXT-CSID</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">94</td>
<td align="left">End.B6.Encaps.Red with NEXT-CSID</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">95</td>
<td align="left">End.BM with NEXT-CSID</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">96</td>
<td align="left">End.LBS with NEXT-CSID</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">97</td>
<td align="left">End.XLBS with NEXT-CSID</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">101</td>
<td align="left">End with REPLACE-CSID</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">102</td>
<td align="left">End with REPLACE-CSID &amp; PSP</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">103</td>
<td align="left">End with REPLACE-CSID &amp; USP</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">104</td>
<td align="left">End with REPLACE-CSID, PSP &amp; USP</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">105</td>
<td align="left">End.X with REPLACE-CSID</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">106</td>
<td align="left">End.X with REPLACE-CSID &amp; PSP</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">107</td>
<td align="left">End.X with REPLACE-CSID &amp; USP</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">108</td>
<td align="left">End.X with REPLACE-CSID, PSP &amp; USP</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">109</td>
<td align="left">End.T with REPLACE-CSID</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">110</td>
<td align="left">End.T with REPLACE-CSID &amp; PSP</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">111</td>
<td align="left">End.T with REPLACE-CSID &amp; USP</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">112</td>
<td align="left">End.T with REPLACE-CSID, PSP &amp; USP</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">114</td>
<td align="left">End.B6.Encaps with REPLACE-CSID</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">115</td>
<td align="left">End.BM with REPLACE-CSID</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">116</td>
<td align="left">End.DX6 with REPLACE-CSID</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">117</td>
<td align="left">End.DX4 with REPLACE-CSID</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">118</td>
<td align="left">End.DT6 with REPLACE-CSID</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">119</td>
<td align="left">End.DT4 with REPLACE-CSID</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">120</td>
<td align="left">End.DT46 with REPLACE-CSID</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">121</td>
<td align="left">End.DX2 with REPLACE-CSID</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">122</td>
<td align="left">End.DX2V with REPLACE-CSID</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">123</td>
<td align="left">End.DT2U with REPLACE-CSID</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">124</td>
<td align="left">End.DT2M with REPLACE-CSID</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">127</td>
<td align="left">End.B6.Encaps.Red with REPLACE-CSID</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">128</td>
<td align="left">End with REPLACE-CSID &amp; USD</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">129</td>
<td align="left">End with REPLACE-CSID, PSP &amp; USD</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">130</td>
<td align="left">End with REPLACE-CSID, USP &amp; USD</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">131</td>
<td align="left">End with REPLACE-CSID, PSP, USP &amp; USD</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">132</td>
<td align="left">End.X with REPLACE-CSID &amp; USD</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">133</td>
<td align="left">End.X with REPLACE-CSID, PSP &amp; USD</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">134</td>
<td align="left">End.X with REPLACE-CSID, USP &amp; USD</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">135</td>
<td align="left">End.X with REPLACE-CSID, PSP, USP &amp; USD</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">136</td>
<td align="left">End.T with REPLACE-CSID &amp; USD</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">137</td>
<td align="left">End.T with REPLACE-CSID, PSP &amp; USD</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">138</td>
<td align="left">End.T with REPLACE-CSID, USP &amp; USD</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">139</td>
<td align="left">End.T with REPLACE-CSID, PSP, USP &amp; USD</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">140</td>
<td align="left">End.LBS with REPLACE-CSID</td>
<td align="left">RFC 9800</td>
</tr>
<tr>
<td align="left">141</td>
<td align="left">End.XLBS with REPLACE-CSID</td>
<td align="left">RFC 9800</td>
</tr>
</tbody>
</table>
</section>
</section>
</middle> </middle>
<back> <back>
<displayreference target="I-D.ietf-idr-bgp-ls-sr-policy" to="BGP-LS-SR"/>
<displayreference target="I-D.ietf-idr-sr-policy-safi" to="SR-BGP"/>
<references anchor="sec-combined-references">
<name>References</name>
<references anchor="sec-normative-references">
<name>Normative References</name>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8
200.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8
402.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8
754.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8
986.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.2
119.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8
174.xml"/>
</references>
<references anchor="sec-informative-references">
<name>Informative References</name>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9
252.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9
259.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9
350.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9
352.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9
513.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9
514.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9
602.xml"/>
<xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9
603.xml"/>
<references title='References' anchor="sec-combined-references"> <!-- [I-D.ietf-idr-bgp-ls-sr-policy]
draft-ietf-idr-bgp-ls-sr-policy-17
<references title='Normative References' anchor="sec-normative-references"> IESG State: RFC Ed Queue as of 03/07/25.
-->
&RFC8200; <reference anchor="I-D.ietf-idr-bgp-ls-sr-policy" target="https://datatracker.ie
&RFC8402; tf.org/doc/html/draft-ietf-idr-bgp-ls-sr-policy-17">
&RFC8754; <front>
&RFC8986; <title>Advertisement of Segment Routing Policies using BGP Link-State</tit
&RFC2119; le>
&RFC8174; <author initials="S." surname="Previdi" fullname="Stefano Previdi">
<organization>Individual</organization>
</references> </author>
<author initials="K." surname="Talaulikar" fullname="Ketan Talaulikar" rol
<references title='Informative References' anchor="sec-informative-reference e="editor">
s"> <organization>Cisco Systems</organization>
</author>
<author initials="J." surname="Dong" fullname="Jie Dong">
<organization>Huawei Technologies</organization>
</author>
<author initials="H." surname="Gredler" fullname="Hannes Gredler">
<organization>RtBrick Inc.</organization>
</author>
<author initials="J." surname="Tantsura" fullname="Jeff Tantsura">
<organization>Nvidia</organization>
</author>
<date month="March" day="6" year="2025" />
</front>
<seriesInfo name="Internet-Draft" value="draft-ietf-idr-bgp-ls-sr-policy-17"
/>
&RFC7942;
&RFC9252;
&RFC9259;
&RFC9350;
&RFC9352;
&RFC9513;
&RFC9514;
&RFC9602;
&RFC9603;
&I-D.ietf-idr-bgp-ls-sr-policy;
&I-D.ietf-idr-sr-policy-safi;
<reference anchor="GKP94" >
<front>
<title>Concrete Mathematics: A Foundation for Computer Science</title>
<author initials="R." surname="Graham" fullname="Ronald Graham">
<organization></organization>
</author>
<author initials="D." surname="Knuth" fullname="Donald Knuth">
<organization></organization>
</author>
<author initials="O." surname="Patashnik" fullname="Oren Patashnik">
<organization></organization>
</author>
<date year="1994"/>
</front>
<seriesInfo name="ISBN" value="9780201558029"/>
</reference>
<reference anchor="SPRING-WG-POLICIES" target="https://wiki.ietf.org/en/group/sp
ring/WG_Policies">
<front>
<title>SPRING Working Group Policies</title>
<author >
<organization>SPRING Working Group Chairs</organization>
</author>
<date year="2022" month="October" day="14"/>
</front>
</reference>
<reference anchor="IMPL-CISCO-NCS540" target="https://www.cisco.com/c/en/us/td/d
ocs/iosxr/ncs5xx/segment-routing/73x/b-segment-routing-cg-73x-ncs540/configure-s
rv6.html">
<front>
<title>Segment Routing Configuration Guide for Cisco NCS 540 Series Routers<
/title>
<author >
<organization>Cisco Systems</organization>
</author>
<date year="2022" month="November" day="02"/>
</front>
</reference>
<reference anchor="IMPL-CISCO-NCS560" target="https://www.cisco.com/c/en/us/td/d
ocs/iosxr/ncs560/segment-routing/76x/b-segment-routing-cg-76x-ncs560/m-configure
-srv6-usid-ncs5xx.html">
<front>
<title>Segment Routing Configuration Guide for Cisco NCS 560 Series Routers<
/title>
<author >
<organization>Cisco Systems</organization>
</author>
<date year="2022" month="October" day="14"/>
</front>
</reference>
<reference anchor="IMPL-CISCO-NCS5500" target="https://www.cisco.com/c/en/us/td/
docs/iosxr/ncs5500/segment-routing/73x/b-segment-routing-cg-ncs5500-73x/configur
e-srv6-micro-sid.html">
<front>
<title>Segment Routing Configuration Guide for Cisco NCS 5500 Series Routers
</title>
<author >
<organization>Cisco Systems</organization>
</author>
<date year="2022" month="November" day="06"/>
</front>
</reference>
<reference anchor="IMPL-CISCO-NCS5700" target="https://www.cisco.com/c/en/us/td/
docs/iosxr/ncs5500/segment-routing/75x/b-segment-routing-cg-ncs5500-75x/configur
e-srv6-micro-sid.html">
<front>
<title>Segment Routing Configuration Guide for Cisco NCS 5700 Series Routers
</title>
<author >
<organization>Cisco Systems</organization>
</author>
<date year="2022" month="November" day="06"/>
</front>
</reference>
<reference anchor="IMPL-CISCO-8000" target="https://www.cisco.com/c/en/us/td/doc
s/iosxr/cisco8000/segment-routing/75x/b-segment-routing-cg-cisco8000-75x/configu
ring-segment-routing-over-ipv6-srv6-micro-sids.html">
<front>
<title>Segment Routing Configuration Guide for Cisco 8000 Series Routers</ti
tle>
<author >
<organization>Cisco Systems</organization>
</author>
<date year="2022" month="November" day="04"/>
</front>
</reference>
<reference anchor="IMPL-CISCO-ASR9000" target="https://www.cisco.com/c/en/us/td/
docs/routers/asr9000/software/asr9k-r7-5/segment-routing/configuration/guide/b-s
egment-routing-cg-asr9000-75x/configure-srv6-micro-sid.html">
<front>
<title>Segment Routing Configuration Guide for Cisco ASR 9000 Series Routers
</title>
<author >
<organization>Cisco Systems</organization>
</author>
<date year="2022" month="November" day="06"/>
</front>
</reference>
<reference anchor="IMPL-NOKIA-20.10" target="https://documentation.nokia.com/sr/
22-10/books/Segment%20Routing%20and%20PCE%20User%20Guide/segment-rout-with-ipv6-
data-plane-srv6.html">
<front>
<title>Segment Routing and PCE User Guide</title>
<author >
<organization>Nokia</organization>
</author>
<date year="2022" month="December"/>
</front>
</reference>
<reference anchor="IMPL-OSS-LINUX" target="https://git.kernel.org/pub/scm/linux/
kernel/git/netdev/net-next.git/commit/?id=cec9d59e89362809f17f2d854faf52966216da
13">
<front>
<title>Add NEXT-CSID support for SRv6 End behavior</title>
<author initials="P." surname="Abeni" fullname="Paolo Abeni">
<organization></organization>
</author>
<date year="2022" month="September" day="20"/>
</front>
</reference>
<reference anchor="IMPL-OSS-SONIC" target="https://github.com/sonic-net/SONiC/bl
ob/master/doc/srv6/SRv6_uSID.md">
<front>
<title>SONiC uSID</title>
<author initials="S." surname="Shah" fullname="Shitanshu Shah">
<organization></organization>
</author>
<author initials="R." surname="Sudarshan" fullname="Reshma Sudarshan">
<organization></organization>
</author>
<date year="2022" month="August" day="21"/>
</front>
</reference>
<reference anchor="IMPL-OSS-SAI" target="https://github.com/opencomputeproject/S
AI/pull/1231/commits/02e58d95ad966ca9efc24eb9e0c0fa10b21de2a4">
<front>
<title>Added new behaviors to support uSID instruction</title>
<author initials="A." surname="Agrawal" fullname="Ashutosh Agrawal">
<organization></organization>
</author>
<date year="2021" month="June" day="08"/>
</front>
</reference>
<reference anchor="IMPL-OSS-VPP" target="https://s3-docs.fd.io/vpp/23.02/cli-ref
erence/clis/clicmd_src_vnet_srv6.html">
<front>
<title>Srv6 cli reference</title>
<author >
<organization>FD.io</organization>
</author>
<date year="n.d."/>
</front>
</reference>
<reference anchor="IMPL-OSS-P4" target="https://github.com/netgroup/p4-srv6-usid
">
<front>
<title>SRv6 uSID (micro SID) implementation on P4</title>
<author initials="S." surname="Salsano" fullname="Stefano Salsano">
<organization></organization>
</author>
<author initials="A." surname="Tulumello" fullname="Angelo Tulumello">
<organization></organization>
</author>
<date year="2021" month="January" day="03"/>
</front>
</reference>
<reference anchor="IMPL-OSS-ONOS" target="https://wiki.opennetworking.org/displa
y/COM/Stratum+CMCC+G-SRv6+Project">
<front>
<title>Stratum CMCC G-SRv6 Project</title>
<author >
<organization>Open Networking Foundation</organization>
</author>
<date year="2021" month="March" day="24"/>
</front>
</reference> </reference>
<reference anchor="IMPL-OSS-OPEN-SRV6" target="http://opensrv6.org.cn/en/srv6-2/
">
<front>
<title>Open SRv6 Project</title>
<author >
<organization></organization>
</author>
<date year="n.d."/>
</front>
</reference>
<reference anchor="EANTC-23" target="https://eantc.de/wp-content/uploads/2023/04
/EANTC-InteropTest2023-TestReport.pdf">
<front>
<title>Multi-Vendor MPLS SDN Interoperability Test Report 2023</title>
<author >
<organization>European Advanced Networking Test Center (EANTC)</organizati
on>
</author>
<date year="2023" month="April" day="18"/>
</front>
</reference>
<reference anchor="EANTC-24" target="https://eantc.de/wp-content/uploads/2023/12
/EANTC-MPLSSDNInterop2024-TestReport-v1.3.pdf">
<front>
<title>Multi-Vendor MPLS SDN Interoperability Test Report 2024</title>
<author >
<organization>European Advanced Networking Test Center (EANTC)</organizati
on>
</author>
<date year="2024" month="April"/>
</front>
</reference>
&RFC4786;
</references> <!-- [I-D.ietf-idr-sr-policy-safi]
draft-ietf-idr-sr-policy-safi-13
</references> IESG State: RFC Ed Queue as of 03/07/25.
-->
<?line 1555?>
<section anchor="complete-pseudocodes"><name>Complete pseudocodes</name>
<t>The content of this section is purely informative rendering of the pseudocode <reference anchor="I-D.ietf-idr-sr-policy-safi" target="https://datatracker.ietf
s of <xref target="RFC8986"/> with the modifications in this document. This rend .org/doc/html/draft-ietf-idr-sr-policy-safi-13">
ering may not be used as a reference.</t> <front>
<title>Advertising Segment Routing Policies in BGP</title>
<author initials="S." surname="Previdi" fullname="Stefano Previdi">
<organization>Huawei Technologies</organization>
</author>
<author initials="C." surname="Filsfils" fullname="Clarence Filsfils">
<organization>Cisco Systems</organization>
</author>
<author initials="K." surname="Talaulikar" fullname="Ketan Talaulikar" rol
e="editor">
<organization>Cisco Systems</organization>
</author>
<author initials="P." surname="Mattes" fullname="Paul Mattes">
<organization>Microsoft</organization>
</author>
<author initials="D." surname="Jain" fullname="Dhanendra Jain">
<organization>Google</organization>
</author>
<date month="February" day="6" year="2025" />
</front>
<seriesInfo name="Internet-Draft" value="draft-ietf-idr-sr-policy-safi-13" />
</reference>
<section anchor="sec-next-end-complete"><name>End with NEXT-CSID</name> <reference anchor="GKP94">
<front>
<title>Concrete Mathematics: A Foundation for Computer Science</titl
e>
<author initials="R." surname="Graham" fullname="Ronald Graham">
<organization/>
</author>
<author initials="D." surname="Knuth" fullname="Donald Knuth">
<organization/>
</author>
<author initials="O." surname="Patashnik" fullname="Oren Patashnik">
<organization/>
</author>
<date year="1994"/>
</front>
<seriesInfo name="ISBN" value="9780201558029"/>
</reference>
<t>When processing the SRH of a packet matching a FIB entry locally instantiated <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.4
as an End SID with the NEXT-CSID flavor:</t> 786.xml"/>
</references>
</references>
<?line 1555?>
<figure><artwork><![CDATA[ <section anchor="complete-pseudocodes">
<name>Complete Pseudocodes</name>
<t>The content of this section is purely informative rendering of the pseu
docodes of <xref target="RFC8986"/> with the modifications in this document. Thi
s rendering may not be used as a reference.</t>
<section anchor="sec-next-end-complete">
<name>End with NEXT-CSID</name>
<t>When processing the SRH of a packet matching a FIB entry locally inst
antiated as an End SID with the NEXT-CSID flavor:</t>
<sourcecode type="pseudocode"><![CDATA[
N01. If (DA.Argument != 0) { N01. If (DA.Argument != 0) {
N02. If (IPv6 Hop Limit <= 1) { N02. If (IPv6 Hop Limit <= 1) {
N03. Send an ICMP Time Exceeded message to the Source Address N03. Send an ICMP Time Exceeded message to the Source Address
with Code 0 (Hop limit exceeded in transit), with Code 0 (Hop limit exceeded in transit),
interrupt packet processing, and discard the packet. interrupt packet processing, and discard the packet.
N04. } N04. }
N05. Copy DA.Argument into the bits [LBL..(LBL+AL-1)] of the N05. Copy DA.Argument into the bits [LBL..(LBL+AL-1)] of the
Destination Address. Destination Address.
N06. Set the bits [(LBL+AL)..127] of the Destination Address to N06. Set the bits [(LBL+AL)..127] of the Destination Address to
zero. zero.
N07. Decrement IPv6 Hop Limit by 1. N07. Decrement IPv6 Hop Limit by 1.
N08. Submit the packet to the egress IPv6 FIB lookup for N08. Submit the packet to the egress IPv6 FIB lookup for
transmission to the next destination. transmission to the next destination.
N09. } N09. }
S02. If (Segments Left == 0) { S02. If (Segments Left == 0) {
S03. Stop processing the SRH, and proceed to process the next S03. Stop processing the SRH and proceed to process the next
header in the packet, whose type is identified by header in the packet, whose type is identified by
the Next Header field in the routing header. the Next Header field in the routing header.
S04. } S04. }
S05. If (IPv6 Hop Limit <= 1) { S05. If (IPv6 Hop Limit <= 1) {
S06. Send an ICMP Time Exceeded message to the Source Address S06. Send an ICMP Time Exceeded message to the Source Address
with Code 0 (Hop limit exceeded in transit), with Code 0 (Hop limit exceeded in transit),
interrupt packet processing, and discard the packet. interrupt packet processing, and discard the packet.
S07. } S07. }
S08. max_LE = (Hdr Ext Len / 2) - 1 S08. max_LE = (Hdr Ext Len / 2) - 1
S09. If ((Last Entry > max_LE) or (Segments Left > Last Entry+1)) { S09. If ((Last Entry > max_LE) or (Segments Left > Last Entry+1)) {
S10. Send an ICMP Parameter Problem to the Source Address S10. Send an ICMP Parameter Problem to the Source Address
with Code 0 (Erroneous header field encountered) with Code 0 (Erroneous header field encountered)
and Pointer set to the Segments Left field, and Pointer set to the Segments Left field,
interrupt packet processing, and discard the packet. interrupt packet processing, and discard the packet.
S11. } S11. }
S12. Decrement IPv6 Hop Limit by 1. S12. Decrement IPv6 Hop Limit by 1.
S13. Decrement Segments Left by 1. S13. Decrement Segments Left by 1.
S14. Update IPv6 DA with Segment List[Segments Left]. S14. Update IPv6 DA with Segment List[Segments Left].
S15. Submit the packet to the egress IPv6 FIB lookup for S15. Submit the packet to the egress IPv6 FIB lookup for
transmission to the new destination. transmission to the new destination.
]]></artwork></figure> ]]></sourcecode>
<t>Before processing the Upper-Layer header or any IPv6 extension header
<t>Before processing the Upper-Layer header or any IPv6 extension header other t other than Hop-by-Hop or Destination Options of a packet matching a FIB entry l
han Hop-by-Hop or Destination Options of a packet matching a FIB entry locally i ocally instantiated as an End SID with the NEXT-CSID flavor:</t>
nstantiated as an End SID with the NEXT-CSID flavor:</t> <sourcecode type="pseudocode"><![CDATA[
<figure><artwork><![CDATA[
N01. If (DA.Argument != 0) { N01. If (DA.Argument != 0) {
N02. If (IPv6 Hop Limit <= 1) { N02. If (IPv6 Hop Limit <= 1) {
N03. Send an ICMP Time Exceeded message to the Source Address, N03. Send an ICMP Time Exceeded message to the Source Address,
Code 0 (Hop limit exceeded in transit), Code 0 (Hop limit exceeded in transit),
interrupt packet processing and discard the packet. interrupt packet processing and discard the packet.
N04. } N04. }
N05. Copy DA.Argument into the bits [LBL..(LBL+AL-1)] of the N05. Copy DA.Argument into the bits [LBL..(LBL+AL-1)] of the
Destination Address. Destination Address.
N06. Set the bits [(LBL+AL)..127] of the Destination Address to N06. Set the bits [(LBL+AL)..127] of the Destination Address to
zero. zero.
N07. Decrement IPv6 Hop Limit by 1. N07. Decrement IPv6 Hop Limit by 1.
N08. Submit the packet to the egress IPv6 FIB lookup for N08. Submit the packet to the egress IPv6 FIB lookup for
transmission to the next destination. transmission to the next destination.
N09. } N09. }
]]></artwork></figure> ]]></sourcecode>
<t>When processing the Upper-Layer header of a packet matching a FIB ent
<t>When processing the Upper-Layer header of a packet matching a FIB entry local ry locally instantiated as an End SID with the NEXT-CSID flavor:</t>
ly instantiated as an End SID with the NEXT-CSID flavor:</t> <sourcecode type="pseudocode"><![CDATA[
<figure><artwork><![CDATA[
S01. If (Upper-Layer header type is allowed by local configuration) { S01. If (Upper-Layer header type is allowed by local configuration) {
S02. Proceed to process the Upper-Layer header S02. Proceed to process the Upper-Layer header
S03. } Else { S03. } Else {
S04. Send an ICMP Parameter Problem to the Source Address S04. Send an ICMP Parameter Problem to the Source Address
with Code 4 (SR Upper-layer Header Error) with Code 4 (SR Upper-layer Header Error)
and Pointer set to the offset of the Upper-Layer header, and Pointer set to the offset of the Upper-Layer header,
interrupt packet processing, and discard the packet. interrupt packet processing, and discard the packet.
S05. } S05. }
]]></artwork></figure> ]]></sourcecode>
</section>
</section> <section anchor="sec-next-endx-complete">
<section anchor="sec-next-endx-complete"><name>End.X with NEXT-CSID</name> <name>End.X with NEXT-CSID</name>
<t>When processing the SRH of a packet matching a FIB entry locally inst
<t>When processing the SRH of a packet matching a FIB entry locally instantiated antiated as an End.X SID with the NEXT-CSID flavor:</t>
as an End.X SID with the NEXT-CSID flavor:</t> <sourcecode type="pseudocode"><![CDATA[
<figure><artwork><![CDATA[
N01. If (DA.Argument != 0) { N01. If (DA.Argument != 0) {
N02. If (IPv6 Hop Limit <= 1) { N02. If (IPv6 Hop Limit <= 1) {
N03. Send an ICMP Time Exceeded message to the Source Address N03. Send an ICMP Time Exceeded message to the Source Address
with Code 0 (Hop limit exceeded in transit), with Code 0 (Hop limit exceeded in transit),
interrupt packet processing, and discard the packet. interrupt packet processing, and discard the packet.
N04. } N04. }
N05. Copy DA.Argument into the bits [LBL..(LBL+AL-1)] of the N05. Copy DA.Argument into the bits [LBL..(LBL+AL-1)] of the
Destination Address. Destination Address.
N06. Set the bits [(LBL+AL)..127] of the Destination Address to N06. Set the bits [(LBL+AL)..127] of the Destination Address to
zero. zero.
N07. Decrement IPv6 Hop Limit by 1. N07. Decrement IPv6 Hop Limit by 1.
N08. Submit the packet to the IPv6 module for transmission to the N08. Submit the packet to the IPv6 module for transmission to the
new destination via a member of J. new destination via a member of J.
N09. } N09. }
S02. If (Segments Left == 0) { S02. If (Segments Left == 0) {
S03. Stop processing the SRH, and proceed to process the next S03. Stop processing the SRH and proceed to process the next
header in the packet, whose type is identified by header in the packet, whose type is identified by
the Next Header field in the routing header. the Next Header field in the routing header.
S04. } S04. }
S05. If (IPv6 Hop Limit <= 1) { S05. If (IPv6 Hop Limit <= 1) {
S06. Send an ICMP Time Exceeded message to the Source Address S06. Send an ICMP Time Exceeded message to the Source Address
with Code 0 (Hop limit exceeded in transit), with Code 0 (Hop limit exceeded in transit),
interrupt packet processing, and discard the packet. interrupt packet processing, and discard the packet.
S07. } S07. }
S08. max_LE = (Hdr Ext Len / 2) - 1 S08. max_LE = (Hdr Ext Len / 2) - 1
S09. If ((Last Entry > max_LE) or (Segments Left > Last Entry+1)) { S09. If ((Last Entry > max_LE) or (Segments Left > Last Entry+1)) {
S10. Send an ICMP Parameter Problem to the Source Address S10. Send an ICMP Parameter Problem to the Source Address
with Code 0 (Erroneous header field encountered) with Code 0 (Erroneous header field encountered)
and Pointer set to the Segments Left field, and Pointer set to the Segments Left field,
interrupt packet processing, and discard the packet. interrupt packet processing, and discard the packet.
S11. } S11. }
S12. Decrement IPv6 Hop Limit by 1. S12. Decrement IPv6 Hop Limit by 1.
S13. Decrement Segments Left by 1. S13. Decrement Segments Left by 1.
S14. Update IPv6 DA with Segment List[Segments Left]. S14. Update IPv6 DA with Segment List[Segments Left].
S15. Submit the packet to the IPv6 module for transmission S15. Submit the packet to the IPv6 module for transmission
to the new destination via a member of J. to the new destination via a member of J.
]]></artwork></figure> ]]></sourcecode>
<t>Before processing the Upper-Layer header or any IPv6 extension header
<t>Before processing the Upper-Layer header or any IPv6 extension header other t other than Hop-by-Hop or Destination Options of a packet matching a FIB entry l
han Hop-by-Hop or Destination Options of a packet matching a FIB entry locally i ocally instantiated as an End.X SID with the NEXT-CSID flavor:</t>
nstantiated as an End.X SID with the NEXT-CSID flavor:</t> <sourcecode type="pseudocode"><![CDATA[
<figure><artwork><![CDATA[
N01. If (DA.Argument != 0) { N01. If (DA.Argument != 0) {
N02. If (IPv6 Hop Limit <= 1) { N02. If (IPv6 Hop Limit <= 1) {
N03. Send an ICMP Time Exceeded message to the Source Address, N03. Send an ICMP Time Exceeded message to the Source Address,
Code 0 (Hop limit exceeded in transit), Code 0 (Hop limit exceeded in transit),
interrupt packet processing and discard the packet. interrupt packet processing and discard the packet.
N04. } N04. }
N05. Copy DA.Argument into the bits [LBL..(LBL+AL-1)] of the N05. Copy DA.Argument into the bits [LBL..(LBL+AL-1)] of the
Destination Address. Destination Address.
N06. Set the bits [(LBL+AL)..127] of the Destination Address to N06. Set the bits [(LBL+AL)..127] of the Destination Address to
zero. zero.
N07. Decrement IPv6 Hop Limit by 1. N07. Decrement IPv6 Hop Limit by 1.
N08. Submit the packet to the IPv6 module for transmission to the N08. Submit the packet to the IPv6 module for transmission to the
new destination via a member of J. new destination via a member of J.
N09. } N09. }
]]></artwork></figure> ]]></sourcecode>
<t>When processing the Upper-Layer header of a packet matching a FIB ent
<t>When processing the Upper-Layer header of a packet matching a FIB entry local ry locally instantiated as an End.X SID with the NEXT-CSID flavor:</t>
ly instantiated as an End.X SID with the NEXT-CSID flavor:</t> <sourcecode type="pseudocode"><![CDATA[
<figure><artwork><![CDATA[
S01. If (Upper-Layer header type is allowed by local configuration) { S01. If (Upper-Layer header type is allowed by local configuration) {
S02. Proceed to process the Upper-Layer header S02. Proceed to process the Upper-Layer header
S03. } Else { S03. } Else {
S04. Send an ICMP Parameter Problem to the Source Address S04. Send an ICMP Parameter Problem to the Source Address
with Code 4 (SR Upper-layer Header Error) with Code 4 (SR Upper-layer Header Error)
and Pointer set to the offset of the Upper-Layer header, and Pointer set to the offset of the Upper-Layer header,
interrupt packet processing, and discard the packet. interrupt packet processing, and discard the packet.
S05. } S05. }
]]></artwork></figure> ]]></sourcecode>
</section>
</section> <section anchor="sec-next-endt-complete">
<section anchor="sec-next-endt-complete"><name>End.T with NEXT-CSID</name> <name>End.T with NEXT-CSID</name>
<t>When processing the SRH of a packet matching a FIB entry locally inst
<t>When processing the SRH of a packet matching a FIB entry locally instantiated antiated as an End.T SID with the NEXT-CSID flavor:</t>
as an End.T SID with the NEXT-CSID flavor:</t> <sourcecode type="pseudocode"><![CDATA[
<figure><artwork><![CDATA[
N01. If (DA.Argument != 0) { N01. If (DA.Argument != 0) {
N02. If (IPv6 Hop Limit <= 1) { N02. If (IPv6 Hop Limit <= 1) {
N03. Send an ICMP Time Exceeded message to the Source Address N03. Send an ICMP Time Exceeded message to the Source Address
with Code 0 (Hop limit exceeded in transit), with Code 0 (Hop limit exceeded in transit),
interrupt packet processing, and discard the packet. interrupt packet processing, and discard the packet.
N04. } N04. }
N05. Copy DA.Argument into the bits [LBL..(LBL+AL-1)] of the N05. Copy DA.Argument into the bits [LBL..(LBL+AL-1)] of the
Destination Address. Destination Address.
N06. Set the bits [(LBL+AL)..127] of the Destination Address to N06. Set the bits [(LBL+AL)..127] of the Destination Address to
zero. zero.
N07. Decrement IPv6 Hop Limit by 1. N07. Decrement IPv6 Hop Limit by 1.
N08.1. Set the packet's associated FIB table to T. N08.1. Set the packet's associated FIB table to T.
N08.2. Submit the packet to the egress IPv6 FIB lookup for N08.2. Submit the packet to the egress IPv6 FIB lookup for
transmission to the new destination. transmission to the new destination.
N09. } N09. }
S02. If (Segments Left == 0) { S02. If (Segments Left == 0) {
S03. Stop processing the SRH, and proceed to process the next S03. Stop processing the SRH and proceed to process the next
header in the packet, whose type is identified by header in the packet, whose type is identified by
the Next Header field in the routing header. the Next Header field in the routing header.
S04. } S04. }
S05. If (IPv6 Hop Limit <= 1) { S05. If (IPv6 Hop Limit <= 1) {
S06. Send an ICMP Time Exceeded message to the Source Address S06. Send an ICMP Time Exceeded message to the Source Address
with Code 0 (Hop limit exceeded in transit), with Code 0 (Hop limit exceeded in transit),
interrupt packet processing, and discard the packet. interrupt packet processing, and discard the packet.
S07. } S07. }
S08. max_LE = (Hdr Ext Len / 2) - 1 S08. max_LE = (Hdr Ext Len / 2) - 1
S09. If ((Last Entry > max_LE) or (Segments Left > Last Entry+1)) { S09. If ((Last Entry > max_LE) or (Segments Left > Last Entry+1)) {
skipping to change at line 2506 skipping to change at line 2237
with Code 0 (Erroneous header field encountered) with Code 0 (Erroneous header field encountered)
and Pointer set to the Segments Left field, and Pointer set to the Segments Left field,
interrupt packet processing, and discard the packet. interrupt packet processing, and discard the packet.
S11. } S11. }
S12. Decrement IPv6 Hop Limit by 1. S12. Decrement IPv6 Hop Limit by 1.
S13. Decrement Segments Left by 1. S13. Decrement Segments Left by 1.
S14. Update IPv6 DA with Segment List[Segments Left]. S14. Update IPv6 DA with Segment List[Segments Left].
S15.1. Set the packet's associated FIB table to T. S15.1. Set the packet's associated FIB table to T.
S15.2. Submit the packet to the egress IPv6 FIB lookup for S15.2. Submit the packet to the egress IPv6 FIB lookup for
transmission to the new destination. transmission to the new destination.
]]></artwork></figure> ]]></sourcecode>
<t>Before processing the Upper-Layer header or any IPv6 extension header
<t>Before processing the Upper-Layer header or any IPv6 extension header other t other than Hop-by-Hop or Destination Options of a packet matching a FIB entry l
han Hop-by-Hop or Destination Options of a packet matching a FIB entry locally i ocally instantiated as an End.T SID with the NEXT-CSID flavor:</t>
nstantiated as an End.T SID with the NEXT-CSID flavor:</t> <sourcecode type="pseudocode"><![CDATA[
<figure><artwork><![CDATA[
N01. If (DA.Argument != 0) { N01. If (DA.Argument != 0) {
N02. If (IPv6 Hop Limit <= 1) { N02. If (IPv6 Hop Limit <= 1) {
N03. Send an ICMP Time Exceeded message to the Source Address, N03. Send an ICMP Time Exceeded message to the Source Address,
Code 0 (Hop limit exceeded in transit), Code 0 (Hop limit exceeded in transit),
interrupt packet processing and discard the packet. interrupt packet processing and discard the packet.
N04. } N04. }
N05. Copy DA.Argument into the bits [LBL..(LBL+AL-1)] of the N05. Copy DA.Argument into the bits [LBL..(LBL+AL-1)] of the
Destination Address. Destination Address.
N06. Set the bits [(LBL+AL)..127] of the Destination Address to N06. Set the bits [(LBL+AL)..127] of the Destination Address to
zero. zero.
N07. Decrement IPv6 Hop Limit by 1. N07. Decrement IPv6 Hop Limit by 1.
N08.1. Set the packet's associated FIB table to T. N08.1. Set the packet's associated FIB table to T.
N08.2. Submit the packet to the egress IPv6 FIB lookup for N08.2. Submit the packet to the egress IPv6 FIB lookup for
transmission to the new destination. transmission to the new destination.
N09. } N09. }
]]></artwork></figure> ]]></sourcecode>
<t>When processing the Upper-Layer header of a packet matching a FIB ent
<t>When processing the Upper-Layer header of a packet matching a FIB entry local ry locally instantiated as an End.T SID with the NEXT-CSID flavor:</t>
ly instantiated as an End.T SID with the NEXT-CSID flavor:</t> <sourcecode type="pseudocode"><![CDATA[
<figure><artwork><![CDATA[
S01. If (Upper-Layer header type is allowed by local configuration) { S01. If (Upper-Layer header type is allowed by local configuration) {
S02. Proceed to process the Upper-Layer header S02. Proceed to process the Upper-Layer header
S03. } Else { S03. } Else {
S04. Send an ICMP Parameter Problem to the Source Address S04. Send an ICMP Parameter Problem to the Source Address
with Code 4 (SR Upper-layer Header Error) with Code 4 (SR Upper-layer Header Error)
and Pointer set to the offset of the Upper-Layer header, and Pointer set to the offset of the Upper-Layer header,
interrupt packet processing, and discard the packet. interrupt packet processing, and discard the packet.
S05. } S05. }
]]></artwork></figure> ]]></sourcecode>
</section>
</section> <section anchor="sec-next-endb6-complete">
<section anchor="sec-next-endb6-complete"><name>End.B6.Encaps with NEXT-CSID</na <name>End.B6.Encaps with NEXT-CSID</name>
me> <t>When processing the SRH of a packet matching a FIB entry locally inst
antiated as an End.B6.Encaps SID with the NEXT-CSID flavor:</t>
<t>When processing the SRH of a packet matching a FIB entry locally instantiated <sourcecode type="pseudocode"><![CDATA[
as an End.B6.Encaps SID with the NEXT-CSID flavor:</t>
<figure><artwork><![CDATA[
N01. If (DA.Argument != 0) { N01. If (DA.Argument != 0) {
N02. If (IPv6 Hop Limit <= 1) { N02. If (IPv6 Hop Limit <= 1) {
N03. Send an ICMP Time Exceeded message to the Source Address, N03. Send an ICMP Time Exceeded message to the Source Address,
Code 0 (Hop limit exceeded in transit), Code 0 (Hop limit exceeded in transit),
interrupt packet processing and discard the packet. interrupt packet processing and discard the packet.
N04. } N04. }
N05. Copy DA.Argument into the bits [LBL..(LBL+AL-1)] of the N05. Copy DA.Argument into the bits [LBL..(LBL+AL-1)] of the
Destination Address. Destination Address.
N06. Set the bits [(LBL+AL)..127] of the Destination Address to N06. Set the bits [(LBL+AL)..127] of the Destination Address to
zero. zero.
N07. Decrement IPv6 Hop Limit by 1. N07. Decrement IPv6 Hop Limit by 1.
N08.1. Push a new IPv6 header with its own SRH containing B. N08.1. Push a new IPv6 header with its own SRH containing B.
N08.2. Set the outer IPv6 SA to A. N08.2. Set the outer IPv6 SA to A.
N08.3. Set the outer IPv6 DA to the first SID of B. N08.3. Set the outer IPv6 DA to the first SID of B.
N08.4. Set the outer Payload Length, Traffic Class, Flow Label, N08.4. Set the outer Payload Length, Traffic Class, Flow Label,
Hop Limit, and Next Header fields. Hop Limit, and Next Header fields.
N08.5. Submit the packet to the egress IPv6 FIB lookup for N08.5. Submit the packet to the egress IPv6 FIB lookup for
transmission to the next destination. transmission to the next destination.
N09. } N09. }
S02. If (Segments Left == 0) { S02. If (Segments Left == 0) {
S03. Stop processing the SRH, and proceed to process the next S03. Stop processing the SRH and proceed to process the next
header in the packet, whose type is identified by header in the packet, whose type is identified by
the Next Header field in the routing header. the Next Header field in the routing header.
S04. } S04. }
S05. If (IPv6 Hop Limit <= 1) { S05. If (IPv6 Hop Limit <= 1) {
S06. Send an ICMP Time Exceeded message to the Source Address S06. Send an ICMP Time Exceeded message to the Source Address
with Code 0 (Hop limit exceeded in transit), with Code 0 (Hop limit exceeded in transit),
interrupt packet processing, and discard the packet. interrupt packet processing, and discard the packet.
S07. } S07. }
S08. max_LE = (Hdr Ext Len / 2) - 1 S08. max_LE = (Hdr Ext Len / 2) - 1
S09. If ((Last Entry > max_LE) or (Segments Left > Last Entry+1)) { S09. If ((Last Entry > max_LE) or (Segments Left > Last Entry+1)) {
skipping to change at line 2593 skipping to change at line 2318
S12. Decrement IPv6 Hop Limit by 1. S12. Decrement IPv6 Hop Limit by 1.
S13. Decrement Segments Left by 1. S13. Decrement Segments Left by 1.
S14. Update IPv6 DA with Segment List[Segments Left]. S14. Update IPv6 DA with Segment List[Segments Left].
S15. Push a new IPv6 header with its own SRH containing B. S15. Push a new IPv6 header with its own SRH containing B.
S16. Set the outer IPv6 SA to A. S16. Set the outer IPv6 SA to A.
S17. Set the outer IPv6 DA to the first SID of B. S17. Set the outer IPv6 DA to the first SID of B.
S18. Set the outer Payload Length, Traffic Class, Flow Label, S18. Set the outer Payload Length, Traffic Class, Flow Label,
Hop Limit, and Next Header fields. Hop Limit, and Next Header fields.
S19. Submit the packet to the egress IPv6 FIB lookup for S19. Submit the packet to the egress IPv6 FIB lookup for
transmission to the new destination. transmission to the new destination.
]]></artwork></figure> ]]></sourcecode>
<t>Before processing the Upper-Layer header or any IPv6 extension header
<t>Before processing the Upper-Layer header or any IPv6 extension header other t other than Hop-by-Hop or Destination Options of a packet matching a FIB entry l
han Hop-by-Hop or Destination Options of a packet matching a FIB entry locally i ocally instantiated as an End.B6.Encaps SID with the NEXT-CSID flavor:</t>
nstantiated as an End.B6.Encaps SID with the NEXT-CSID flavor:</t> <sourcecode type="pseudocode"><![CDATA[
<figure><artwork><![CDATA[
N01. If (DA.Argument != 0) { N01. If (DA.Argument != 0) {
N02. If (IPv6 Hop Limit <= 1) { N02. If (IPv6 Hop Limit <= 1) {
N03. Send an ICMP Time Exceeded message to the Source Address, N03. Send an ICMP Time Exceeded message to the Source Address,
Code 0 (Hop limit exceeded in transit), Code 0 (Hop limit exceeded in transit),
interrupt packet processing and discard the packet. interrupt packet processing and discard the packet.
N04. } N04. }
N05. Copy DA.Argument into the bits [LBL..(LBL+AL-1)] of the N05. Copy DA.Argument into the bits [LBL..(LBL+AL-1)] of the
Destination Address. Destination Address.
N06. Set the bits [(LBL+AL)..127] of the Destination Address to N06. Set the bits [(LBL+AL)..127] of the Destination Address to
zero. zero.
N07. Decrement IPv6 Hop Limit by 1. N07. Decrement IPv6 Hop Limit by 1.
N08.1. Push a new IPv6 header with its own SRH containing B. N08.1. Push a new IPv6 header with its own SRH containing B.
N08.2. Set the outer IPv6 SA to A. N08.2. Set the outer IPv6 SA to A.
N08.3. Set the outer IPv6 DA to the first SID of B. N08.3. Set the outer IPv6 DA to the first SID of B.
N08.4. Set the outer Payload Length, Traffic Class, Flow Label, N08.4. Set the outer Payload Length, Traffic Class, Flow Label,
Hop Limit, and Next Header fields. Hop Limit, and Next Header fields.
N08.5. Submit the packet to the egress IPv6 FIB lookup for N08.5. Submit the packet to the egress IPv6 FIB lookup for
transmission to the next destination. transmission to the next destination.
N09. } N09. }
]]></artwork></figure> ]]></sourcecode>
<t>When processing the Upper-Layer header of a packet matching a FIB ent
<t>When processing the Upper-Layer header of a packet matching a FIB entry local ry locally instantiated as an End.B6.Encaps SID with the NEXT-CSID flavor:</t>
ly instantiated as an End.B6.Encaps SID with the NEXT-CSID flavor:</t> <sourcecode type="pseudocode"><![CDATA[
<figure><artwork><![CDATA[
S01. If (Upper-Layer header type is allowed by local configuration) { S01. If (Upper-Layer header type is allowed by local configuration) {
S02. Proceed to process the Upper-Layer header S02. Proceed to process the Upper-Layer header
S03. } Else { S03. } Else {
S04. Send an ICMP Parameter Problem to the Source Address S04. Send an ICMP Parameter Problem to the Source Address
with Code 4 (SR Upper-layer Header Error) with Code 4 (SR Upper-layer Header Error)
and Pointer set to the offset of the Upper-Layer header, and Pointer set to the offset of the Upper-Layer header,
interrupt packet processing, and discard the packet. interrupt packet processing, and discard the packet.
S05. } S05. }
]]></artwork></figure> ]]></sourcecode>
</section>
</section> <section anchor="sec-next-endbm-complete">
<section anchor="sec-next-endbm-complete"><name>End.BM with NEXT-CSID</name> <name>End.BM with NEXT-CSID</name>
<t>When processing the SRH of a packet matching a FIB entry locally inst
<t>When processing the SRH of a packet matching a FIB entry locally instantiated antiated as an End.BM SID with the NEXT-CSID flavor:</t>
as an End.BM SID with the NEXT-CSID flavor:</t> <sourcecode type="pseudocode"><![CDATA[
<figure><artwork><![CDATA[
N01. If (DA.Argument != 0) { N01. If (DA.Argument != 0) {
N02. If (IPv6 Hop Limit <= 1) { N02. If (IPv6 Hop Limit <= 1) {
N03. Send an ICMP Time Exceeded message to the Source Address, N03. Send an ICMP Time Exceeded message to the Source Address,
Code 0 (Hop limit exceeded in transit), Code 0 (Hop limit exceeded in transit),
interrupt packet processing and discard the packet. interrupt packet processing and discard the packet.
N04. } N04. }
N05. Copy DA.Argument into the bits [LBL..(LBL+AL-1)] of the N05. Copy DA.Argument into the bits [LBL..(LBL+AL-1)] of the
Destination Address. Destination Address.
N06. Set the bits [(LBL+AL)..127] of the Destination Address to N06. Set the bits [(LBL+AL)..127] of the Destination Address to
zero. zero.
N07. Decrement IPv6 Hop Limit by 1. N07. Decrement IPv6 Hop Limit by 1.
N08.1. Push the MPLS label stack for B. N08.1. Push the MPLS label stack for B.
N08.2. Submit the packet to the MPLS engine for transmission. N08.2. Submit the packet to the MPLS engine for transmission.
N09. } N09. }
S02. If (Segments Left == 0) { S02. If (Segments Left == 0) {
S03. Stop processing the SRH, and proceed to process the next S03. Stop processing the SRH and proceed to process the next
header in the packet, whose type is identified by header in the packet, whose type is identified by
the Next Header field in the routing header. the Next Header field in the routing header.
S04. } S04. }
S05. If (IPv6 Hop Limit <= 1) { S05. If (IPv6 Hop Limit <= 1) {
S06. Send an ICMP Time Exceeded message to the Source Address S06. Send an ICMP Time Exceeded message to the Source Address
with Code 0 (Hop limit exceeded in transit), with Code 0 (Hop limit exceeded in transit),
interrupt packet processing, and discard the packet. interrupt packet processing, and discard the packet.
S07. } S07. }
S08. max_LE = (Hdr Ext Len / 2) - 1 S08. max_LE = (Hdr Ext Len / 2) - 1
S09. If ((Last Entry > max_LE) or (Segments Left > Last Entry+1)) { S09. If ((Last Entry > max_LE) or (Segments Left > Last Entry+1)) {
S10. Send an ICMP Parameter Problem to the Source Address S10. Send an ICMP Parameter Problem to the Source Address
with Code 0 (Erroneous header field encountered) with Code 0 (Erroneous header field encountered)
and Pointer set to the Segments Left field, and Pointer set to the Segments Left field,
interrupt packet processing, and discard the packet. interrupt packet processing, and discard the packet.
S11. } S11. }
S12. Decrement IPv6 Hop Limit by 1. S12. Decrement IPv6 Hop Limit by 1.
S13. Decrement Segments Left by 1. S13. Decrement Segments Left by 1.
S14. Update IPv6 DA with Segment List[Segments Left]. S14. Update IPv6 DA with Segment List[Segments Left].
S15. Push the MPLS label stack for B. S15. Push the MPLS label stack for B.
S16. Submit the packet to the MPLS engine for transmission. S16. Submit the packet to the MPLS engine for transmission.
]]></artwork></figure> ]]></sourcecode>
<t>Before processing the Upper-Layer header or any IPv6 extension header
<t>Before processing the Upper-Layer header or any IPv6 extension header other t other than Hop-by-Hop or Destination Options of a packet matching a FIB entry l
han Hop-by-Hop or Destination Options of a packet matching a FIB entry locally i ocally instantiated as an End.BM SID with the NEXT-CSID flavor:</t>
nstantiated as an End.BM SID with the NEXT-CSID flavor:</t> <sourcecode type="pseudocode"><![CDATA[
<figure><artwork><![CDATA[
N01. If (DA.Argument != 0) { N01. If (DA.Argument != 0) {
N02. If (IPv6 Hop Limit <= 1) { N02. If (IPv6 Hop Limit <= 1) {
N03. Send an ICMP Time Exceeded message to the Source Address, N03. Send an ICMP Time Exceeded message to the Source Address,
Code 0 (Hop limit exceeded in transit), Code 0 (Hop limit exceeded in transit),
interrupt packet processing and discard the packet. interrupt packet processing and discard the packet.
N04. } N04. }
N05. Copy DA.Argument into the bits [LBL..(LBL+AL-1)] of the N05. Copy DA.Argument into the bits [LBL..(LBL+AL-1)] of the
Destination Address. Destination Address.
N06. Set the bits [(LBL+AL)..127] of the Destination Address to N06. Set the bits [(LBL+AL)..127] of the Destination Address to
zero. zero.
N07. Decrement IPv6 Hop Limit by 1. N07. Decrement IPv6 Hop Limit by 1.
N08.1. Push the MPLS label stack for B. N08.1. Push the MPLS label stack for B.
N08.2. Submit the packet to the MPLS engine for transmission. N08.2. Submit the packet to the MPLS engine for transmission.
N09. } N09. }
]]></artwork></figure> ]]></sourcecode>
<t>When processing the Upper-Layer header of a packet matching a FIB ent
<t>When processing the Upper-Layer header of a packet matching a FIB entry local ry locally instantiated as an End.BM SID with the NEXT-CSID flavor:</t>
ly instantiated as an End.BM SID with the NEXT-CSID flavor:</t> <sourcecode type="pseudocode"><![CDATA[
<figure><artwork><![CDATA[
S01. If (Upper-Layer header type is allowed by local configuration) { S01. If (Upper-Layer header type is allowed by local configuration) {
S02. Proceed to process the Upper-Layer header S02. Proceed to process the Upper-Layer header
S03. } Else { S03. } Else {
S04. Send an ICMP Parameter Problem to the Source Address S04. Send an ICMP Parameter Problem to the Source Address
with Code 4 (SR Upper-layer Header Error) with Code 4 (SR Upper-layer Header Error)
and Pointer set to the offset of the Upper-Layer header, and Pointer set to the offset of the Upper-Layer header,
interrupt packet processing, and discard the packet. interrupt packet processing, and discard the packet.
S05. } S05. }
]]></artwork></figure> ]]></sourcecode>
</section>
</section> <section anchor="sec-replace-end-complete">
<section anchor="sec-replace-end-complete"><name>End with REPLACE-CSID</name> <name>End with REPLACE-CSID</name>
<t>When processing the SRH of a packet matching a FIB entry locally inst
<t>When processing the SRH of a packet matching a FIB entry locally instantiated antiated as an End SID with the REPLACE-CSID flavor:</t>
as an End SID with the REPLACE-CSID flavor:</t> <sourcecode type="pseudocode"><![CDATA[
<figure><artwork><![CDATA[
S01. When an SRH is processed { S01. When an SRH is processed {
S02. If (Segments Left == 0 and (DA.Arg.Index == 0 or S02. If (Segments Left == 0 and (DA.Arg.Index == 0 or
Segment List[0][DA.Arg.Index-1] == 0)) { Segment List[0][DA.Arg.Index-1] == 0)) {
S03. Stop processing the SRH, and proceed to process the next S03. Stop processing the SRH and proceed to process the next
header in the packet, whose type is identified by header in the packet, whose type is identified by
the Next Header field in the routing header. the Next Header field in the routing header.
S04. } S04. }
S05. If (IPv6 Hop Limit <= 1) { S05. If (IPv6 Hop Limit <= 1) {
S06. Send an ICMP Time Exceeded message to the Source Address, S06. Send an ICMP Time Exceeded message to the Source Address,
Code 0 (Hop limit exceeded in transit), Code 0 (Hop limit exceeded in transit),
interrupt packet processing and discard the packet. interrupt packet processing and discard the packet.
S07. } S07. }
S08. max_LE = (Hdr Ext Len / 2) - 1 S08. max_LE = (Hdr Ext Len / 2) - 1
R01. If (DA.Arg.Index != 0) { R01. If (DA.Arg.Index != 0) {
skipping to change at line 2759 skipping to change at line 2472
R16. Decrement Segments Left by 1. R16. Decrement Segments Left by 1.
R17. Set DA.Arg.Index to (128/LNFL - 1). R17. Set DA.Arg.Index to (128/LNFL - 1).
R18. } R18. }
R19. Decrement IPv6 Hop Limit by 1. R19. Decrement IPv6 Hop Limit by 1.
R20. Write Segment List[Segments Left][DA.Arg.Index] into the bits R20. Write Segment List[Segments Left][DA.Arg.Index] into the bits
[LBL..LBL+LNFL-1] of the Destination Address of the IPv6 [LBL..LBL+LNFL-1] of the Destination Address of the IPv6
header. header.
R21. Submit the packet to the egress IPv6 FIB lookup for R21. Submit the packet to the egress IPv6 FIB lookup for
transmission to the new destination. transmission to the new destination.
S16. } S16. }
]]></artwork></figure> ]]></sourcecode>
<t>When processing the Upper-Layer header of a packet matching a FIB ent
<t>When processing the Upper-Layer header of a packet matching a FIB entry local ry locally instantiated as an End SID with the REPLACE-CSID flavor:</t>
ly instantiated as an End SID with the REPLACE-CSID flavor:</t> <sourcecode type="pseudocode"><![CDATA[
<figure><artwork><![CDATA[
S01. If (Upper-Layer header type is allowed by local configuration) { S01. If (Upper-Layer header type is allowed by local configuration) {
S02. Proceed to process the Upper-Layer header S02. Proceed to process the Upper-Layer header
S03. } Else { S03. } Else {
S04. Send an ICMP Parameter Problem to the Source Address S04. Send an ICMP Parameter Problem to the Source Address
with Code 4 (SR Upper-layer Header Error) with Code 4 (SR Upper-layer Header Error)
and Pointer set to the offset of the Upper-Layer header, and Pointer set to the offset of the Upper-Layer header,
interrupt packet processing, and discard the packet. interrupt packet processing, and discard the packet.
S05. } S05. }
]]></artwork></figure> ]]></sourcecode>
</section>
</section> <section anchor="sec-replace-endx-complete">
<section anchor="sec-replace-endx-complete"><name>End.X with REPLACE-CSID</name> <name>End.X with REPLACE-CSID</name>
<t>When processing the SRH of a packet matching a FIB entry locally inst
<t>When processing the SRH of a packet matching a FIB entry locally instantiated antiated as an End.X SID with the REPLACE-CSID flavor:</t>
as an End.X SID with the REPLACE-CSID flavor:</t> <sourcecode type="pseudocode"><![CDATA[
<figure><artwork><![CDATA[
S01. When an SRH is processed { S01. When an SRH is processed {
S02. If (Segments Left == 0 and (DA.Arg.Index == 0 or S02. If (Segments Left == 0 and (DA.Arg.Index == 0 or
Segment List[0][DA.Arg.Index-1] == 0)) { Segment List[0][DA.Arg.Index-1] == 0)) {
S03. Stop processing the SRH, and proceed to process the next S03. Stop processing the SRH and proceed to process the next
header in the packet, whose type is identified by header in the packet, whose type is identified by
the Next Header field in the routing header. the Next Header field in the routing header.
S04. } S04. }
S05. If (IPv6 Hop Limit <= 1) { S05. If (IPv6 Hop Limit <= 1) {
S06. Send an ICMP Time Exceeded message to the Source Address, S06. Send an ICMP Time Exceeded message to the Source Address,
Code 0 (Hop limit exceeded in transit), Code 0 (Hop limit exceeded in transit),
interrupt packet processing and discard the packet. interrupt packet processing and discard the packet.
S07. } S07. }
S08. max_LE = (Hdr Ext Len / 2) - 1 S08. max_LE = (Hdr Ext Len / 2) - 1
R01. If (DA.Arg.Index != 0) { R01. If (DA.Arg.Index != 0) {
skipping to change at line 2825 skipping to change at line 2534
R16. Decrement Segments Left by 1. R16. Decrement Segments Left by 1.
R17. Set DA.Arg.Index to (128/LNFL - 1). R17. Set DA.Arg.Index to (128/LNFL - 1).
R18. } R18. }
R19. Decrement IPv6 Hop Limit by 1. R19. Decrement IPv6 Hop Limit by 1.
R20. Write Segment List[Segments Left][DA.Arg.Index] into the bits R20. Write Segment List[Segments Left][DA.Arg.Index] into the bits
[LBL..LBL+LNFL-1] of the Destination Address of the IPv6 [LBL..LBL+LNFL-1] of the Destination Address of the IPv6
header. header.
R21. Submit the packet to the IPv6 module for transmission to the R21. Submit the packet to the IPv6 module for transmission to the
new destination via a member of J. new destination via a member of J.
S16. } S16. }
]]></artwork></figure> ]]></sourcecode>
<t>When processing the Upper-Layer header of a packet matching a FIB ent
<t>When processing the Upper-Layer header of a packet matching a FIB entry local ry locally instantiated as an End.X SID with the REPLACE-CSID flavor:</t>
ly instantiated as an End.X SID with the REPLACE-CSID flavor:</t> <sourcecode type="pseudocode"><![CDATA[
<figure><artwork><![CDATA[
S01. If (Upper-Layer header type is allowed by local configuration) { S01. If (Upper-Layer header type is allowed by local configuration) {
S02. Proceed to process the Upper-Layer header S02. Proceed to process the Upper-Layer header
S03. } Else { S03. } Else {
S04. Send an ICMP Parameter Problem to the Source Address S04. Send an ICMP Parameter Problem to the Source Address
with Code 4 (SR Upper-layer Header Error) with Code 4 (SR Upper-layer Header Error)
and Pointer set to the offset of the Upper-Layer header, and Pointer set to the offset of the Upper-Layer header,
interrupt packet processing, and discard the packet. interrupt packet processing, and discard the packet.
S05. } S05. }
]]></artwork></figure> ]]></sourcecode>
</section>
</section> <section anchor="sec-replace-endt-complete">
<section anchor="sec-replace-endt-complete"><name>End.T with REPLACE-CSID</name> <name>End.T with REPLACE-CSID</name>
<t>When processing the SRH of a packet matching a FIB entry locally inst
<t>When processing the SRH of a packet matching a FIB entry locally instantiated antiated as an End.T SID with the REPLACE-CSID flavor:</t>
as an End.T SID with the REPLACE-CSID flavor:</t> <sourcecode type="pseudocode"><![CDATA[
<figure><artwork><![CDATA[
S01. When an SRH is processed { S01. When an SRH is processed {
S02. If (Segments Left == 0 and (DA.Arg.Index == 0 or S02. If (Segments Left == 0 and (DA.Arg.Index == 0 or
Segment List[0][DA.Arg.Index-1] == 0)) { Segment List[0][DA.Arg.Index-1] == 0)) {
S03. Stop processing the SRH, and proceed to process the next S03. Stop processing the SRH and proceed to process the next
header in the packet, whose type is identified by header in the packet, whose type is identified by
the Next Header field in the routing header. the Next Header field in the routing header.
S04. } S04. }
S05. If (IPv6 Hop Limit <= 1) { S05. If (IPv6 Hop Limit <= 1) {
S06. Send an ICMP Time Exceeded message to the Source Address, S06. Send an ICMP Time Exceeded message to the Source Address,
Code 0 (Hop limit exceeded in transit), Code 0 (Hop limit exceeded in transit),
interrupt packet processing and discard the packet. interrupt packet processing and discard the packet.
S07. } S07. }
S08. max_LE = (Hdr Ext Len / 2) - 1 S08. max_LE = (Hdr Ext Len / 2) - 1
R01. If (DA.Arg.Index != 0) { R01. If (DA.Arg.Index != 0) {
skipping to change at line 2893 skipping to change at line 2598
R17. Set DA.Arg.Index to (128/LNFL - 1). R17. Set DA.Arg.Index to (128/LNFL - 1).
R18. } R18. }
R19. Decrement IPv6 Hop Limit by 1. R19. Decrement IPv6 Hop Limit by 1.
R20. Write Segment List[Segments Left][DA.Arg.Index] into the bits R20. Write Segment List[Segments Left][DA.Arg.Index] into the bits
[LBL..LBL+LNFL-1] of the Destination Address of the IPv6 [LBL..LBL+LNFL-1] of the Destination Address of the IPv6
header. header.
R21.1. Set the packet's associated FIB table to T. R21.1. Set the packet's associated FIB table to T.
R21.2. Submit the packet to the egress IPv6 FIB lookup for R21.2. Submit the packet to the egress IPv6 FIB lookup for
transmission to the new destination. transmission to the new destination.
S16. } S16. }
]]></artwork></figure> ]]></sourcecode>
<t>When processing the Upper-Layer header of a packet matching a FIB ent
<t>When processing the Upper-Layer header of a packet matching a FIB entry local ry locally instantiated as an End.T SID with the REPLACE-CSID flavor:</t>
ly instantiated as an End.T SID with the REPLACE-CSID flavor:</t> <sourcecode type="pseudocode"><![CDATA[
<figure><artwork><![CDATA[
S01. If (Upper-Layer header type is allowed by local configuration) { S01. If (Upper-Layer header type is allowed by local configuration) {
S02. Proceed to process the Upper-Layer header S02. Proceed to process the Upper-Layer header
S03. } Else { S03. } Else {
S04. Send an ICMP Parameter Problem to the Source Address S04. Send an ICMP Parameter Problem to the Source Address
with Code 4 (SR Upper-layer Header Error) with Code 4 (SR Upper-layer Header Error)
and Pointer set to the offset of the Upper-Layer header, and Pointer set to the offset of the Upper-Layer header,
interrupt packet processing, and discard the packet. interrupt packet processing, and discard the packet.
S05. } S05. }
]]></artwork></figure> ]]></sourcecode>
</section>
</section> <section anchor="sec-replace-endb6-complete">
<section anchor="sec-replace-endb6-complete"><name>End.B6.Encaps with REPLACE-CS <name>End.B6.Encaps with REPLACE-CSID</name>
ID</name> <t>When processing the SRH of a packet matching a FIB entry locally inst
antiated as an End.B6.Encaps SID with the REPLACE-CSID flavor:</t>
<t>When processing the SRH of a packet matching a FIB entry locally instantiated <sourcecode type="pseudocode"><![CDATA[
as an End.B6.Encaps SID with the REPLACE-CSID flavor:</t>
<figure><artwork><![CDATA[
S01. When an SRH is processed { S01. When an SRH is processed {
S02. If (Segments Left == 0 and (DA.Arg.Index == 0 or S02. If (Segments Left == 0 and (DA.Arg.Index == 0 or
Segment List[0][DA.Arg.Index-1] == 0)) { Segment List[0][DA.Arg.Index-1] == 0)) {
S03. Stop processing the SRH, and proceed to process the next S03. Stop processing the SRH and proceed to process the next
header in the packet, whose type is identified by header in the packet, whose type is identified by
the Next Header field in the routing header. the Next Header field in the routing header.
S04. } S04. }
S05. If (IPv6 Hop Limit <= 1) { S05. If (IPv6 Hop Limit <= 1) {
S06. Send an ICMP Time Exceeded message to the Source Address, S06. Send an ICMP Time Exceeded message to the Source Address,
Code 0 (Hop limit exceeded in transit), Code 0 (Hop limit exceeded in transit),
interrupt packet processing and discard the packet. interrupt packet processing and discard the packet.
S07. } S07. }
S08. max_LE = (Hdr Ext Len / 2) - 1 S08. max_LE = (Hdr Ext Len / 2) - 1
R01. If (DA.Arg.Index != 0) { R01. If (DA.Arg.Index != 0) {
skipping to change at line 2969 skipping to change at line 2670
[LBL..LBL+LNFL-1] of the Destination Address of the IPv6 [LBL..LBL+LNFL-1] of the Destination Address of the IPv6
header. header.
R21.1. Push a new IPv6 header with its own SRH containing B. R21.1. Push a new IPv6 header with its own SRH containing B.
R21.2. Set the outer IPv6 SA to A. R21.2. Set the outer IPv6 SA to A.
R21.3. Set the outer IPv6 DA to the first SID of B. R21.3. Set the outer IPv6 DA to the first SID of B.
R21.4. Set the outer Payload Length, Traffic Class, Flow Label, R21.4. Set the outer Payload Length, Traffic Class, Flow Label,
Hop Limit, and Next Header fields. Hop Limit, and Next Header fields.
R21.5. Submit the packet to the egress IPv6 FIB lookup for R21.5. Submit the packet to the egress IPv6 FIB lookup for
transmission to the next destination. transmission to the next destination.
S16. } S16. }
]]></artwork></figure> ]]></sourcecode>
<t>When processing the Upper-Layer header of a packet matching a FIB ent
<t>When processing the Upper-Layer header of a packet matching a FIB entry local ry locally instantiated as an End.B6.Encaps SID with the REPLACE-CSID flavor:</t
ly instantiated as an End.B6.Encaps SID with the REPLACE-CSID flavor:</t> >
<sourcecode type="pseudocode"><![CDATA[
<figure><artwork><![CDATA[
S01. If (Upper-Layer header type is allowed by local configuration) { S01. If (Upper-Layer header type is allowed by local configuration) {
S02. Proceed to process the Upper-Layer header S02. Proceed to process the Upper-Layer header
S03. } Else { S03. } Else {
S04. Send an ICMP Parameter Problem to the Source Address S04. Send an ICMP Parameter Problem to the Source Address
with Code 4 (SR Upper-layer Header Error) with Code 4 (SR Upper-layer Header Error)
and Pointer set to the offset of the Upper-Layer header, and Pointer set to the offset of the Upper-Layer header,
interrupt packet processing, and discard the packet. interrupt packet processing, and discard the packet.
S05. } S05. }
]]></artwork></figure> ]]></sourcecode>
</section>
</section> <section anchor="sec-replace-endbm-complete">
<section anchor="sec-replace-endbm-complete"><name>End.BM with REPLACE-CSID</nam <name>End.BM with REPLACE-CSID</name>
e> <t>When processing the SRH of a packet matching a FIB entry locally inst
antiated as an End.BM SID with the REPLACE-CSID flavor:</t>
<t>When processing the SRH of a packet matching a FIB entry locally instantiated <sourcecode type="pseudocode"><![CDATA[
as an End.BM SID with the REPLACE-CSID flavor:</t>
<figure><artwork><![CDATA[
S01. When an SRH is processed { S01. When an SRH is processed {
S02. If (Segments Left == 0 and (DA.Arg.Index == 0 or S02. If (Segments Left == 0 and (DA.Arg.Index == 0 or
Segment List[0][DA.Arg.Index-1] == 0)) { Segment List[0][DA.Arg.Index-1] == 0)) {
S03. Stop processing the SRH, and proceed to process the next S03. Stop processing the SRH and proceed to process the next
header in the packet, whose type is identified by header in the packet, whose type is identified by
the Next Header field in the routing header. the Next Header field in the routing header.
S04. } S04. }
S05. If (IPv6 Hop Limit <= 1) { S05. If (IPv6 Hop Limit <= 1) {
S06. Send an ICMP Time Exceeded message to the Source Address, S06. Send an ICMP Time Exceeded message to the Source Address,
Code 0 (Hop limit exceeded in transit), Code 0 (Hop limit exceeded in transit),
interrupt packet processing and discard the packet. interrupt packet processing and discard the packet.
S07. } S07. }
S08. max_LE = (Hdr Ext Len / 2) - 1 S08. max_LE = (Hdr Ext Len / 2) - 1
R01. If (DA.Arg.Index != 0) { R01. If (DA.Arg.Index != 0) {
skipping to change at line 3035 skipping to change at line 2732
R16. Decrement Segments Left by 1. R16. Decrement Segments Left by 1.
R17. Set DA.Arg.Index to (128/LNFL - 1). R17. Set DA.Arg.Index to (128/LNFL - 1).
R18. } R18. }
R19. Decrement IPv6 Hop Limit by 1. R19. Decrement IPv6 Hop Limit by 1.
R20. Write Segment List[Segments Left][DA.Arg.Index] into the bits R20. Write Segment List[Segments Left][DA.Arg.Index] into the bits
[LBL..LBL+LNFL-1] of the Destination Address of the IPv6 [LBL..LBL+LNFL-1] of the Destination Address of the IPv6
header. header.
R21.1. Push the MPLS label stack for B. R21.1. Push the MPLS label stack for B.
R21.2. Submit the packet to the MPLS engine for transmission. R21.2. Submit the packet to the MPLS engine for transmission.
S16. } S16. }
]]></artwork></figure> ]]></sourcecode>
<t>When processing the Upper-Layer header of a packet matching a FIB ent
<t>When processing the Upper-Layer header of a packet matching a FIB entry local ry locally instantiated as an End.BM SID with the REPLACE-CSID flavor:</t>
ly instantiated as an End.BM SID with the REPLACE-CSID flavor:</t> <sourcecode type="pseudocode"><![CDATA[
<figure><artwork><![CDATA[
S01. If (Upper-Layer header type is allowed by local configuration) { S01. If (Upper-Layer header type is allowed by local configuration) {
S02. Proceed to process the Upper-Layer header S02. Proceed to process the Upper-Layer header
S03. } Else { S03. } Else {
S04. Send an ICMP Parameter Problem to the Source Address S04. Send an ICMP Parameter Problem to the Source Address
with Code 4 (SR Upper-layer Header Error) with Code 4 (SR Upper-layer Header Error)
and Pointer set to the offset of the Upper-Layer header, and Pointer set to the offset of the Upper-Layer header,
interrupt packet processing, and discard the packet. interrupt packet processing, and discard the packet.
S05. } S05. }
]]></artwork></figure> ]]></sourcecode>
</section>
</section>
</section> <section anchor="acknowledgements" numbered="false" toc="include">
</section> <name>Acknowledgements</name>
<t>The authors would like to thank <contact fullname="Kamran Raza"/>, <con
tact fullname="Xing Jiang"/>, <contact fullname="YuanChao Su"/>, <contact fullna
me="Han Li"/>, <contact fullname="Yisong Liu"/>, <contact fullname="Martin Vigou
reux"/>, <contact fullname="Joel Halpern"/>, and <contact fullname="Tal Mizrahi"
/> for their insightful feedback and suggestions.</t>
<t>The authors would also like to thank <contact fullname="Andrew Alston"/
>, <contact fullname="Linda Dunbar"/>, <contact fullname="Adrian Farrel"/>, <con
tact fullname="Boris Hassanov"/>, <contact fullname="Alvaro Retana"/>, and <cont
act fullname="Gunter Van de Velde"/> for their thorough review of this document.
</t>
</section>
<section anchor="contributors" numbered="false" toc="include" removeInRFC="f alse"> <section anchor="contributors" numbered="false" toc="include" removeInRFC="f alse">
<name>Contributors</name> <name>Contributors</name>
<contact initials="L." surname="Aihua" fullname="Liu Aihua"> <contact initials="L." surname="Aihua" fullname="Liu Aihua">
<organization>ZTE Corporation</organization> <organization>ZTE Corporation</organization>
<address> <address>
<postal> <postal>
<country>China</country> <country>China</country>
</postal> </postal>
<email>liu.aihua@zte.com.cn</email> <email>liu.aihua@zte.com.cn</email>
</address> </address>
</contact> </contact>
<contact initials="D." surname="Cai" fullname="Dennis Cai"> <contact initials="D." surname="Cai" fullname="Dennis Cai">
<organization>Alibaba</organization> <organization>Alibaba</organization>
<address> <address>
<postal> <postal>
<country>USA</country> <country>USA</country>
</postal> </postal>
<email>d.cai@alibaba-inc.com</email> <email>d.cai@alibaba-inc.com</email>
</address> </address>
</contact> </contact>
<contact initials="D." surname="Dukes" fullname="Darren Dukes"> <contact initials="D." surname="Dukes" fullname="Darren Dukes">
<organization>Cisco Systems, Inc.</organization> <organization>Cisco Systems, Inc.</organization>
<address> <address>
<postal> <postal>
<country>Canada</country> <country>Canada</country>
</postal> </postal>
<email>ddukes@cisco.com</email> <email>ddukes@cisco.com</email>
</address> </address>
</contact> </contact>
<contact initials="J." surname="Guichard" fullname="James N Guichard"> <contact initials="J." surname="Guichard" fullname="James N Guichard">
<organization>Futurewei Technologies Ltd.</organization> <organization>Futurewei Technologies Ltd.</organization>
<address> <address>
<postal> <postal>
<country>USA</country> <country>USA</country>
</postal> </postal>
<email>james.n.guichard@futurewei.com</email> <email>james.n.guichard@futurewei.com</email>
</address> </address>
</contact> </contact>
<contact initials="C." surname="Li" fullname="Cheng Li"> <contact initials="C." surname="Li" fullname="Cheng Li">
<organization>Huawei Technologies</organization> <organization>Huawei Technologies</organization>
<address> <address>
<postal> <postal>
<country>China</country> <country>China</country>
</postal> </postal>
<email>c.l@huawei.com</email> <email>c.l@huawei.com</email>
</address> </address>
</contact> </contact>
<contact initials="R." surname="Raszuk" fullname="Robert Raszuk"> <contact initials="R." surname="Raszuk" fullname="Robert Raszuk">
<organization>NTT Network Innovations</organization> <organization>NTT Network Innovations</organization>
<address> <address>
<postal> <postal>
<country>USA</country> <country>USA</country>
</postal> </postal>
<email>robert@raszuk.net</email> <email>robert@raszuk.net</email>
</address> </address>
</contact> </contact>
<contact initials="K." surname="Talaulikar" fullname="Ketan Talaulikar"> <contact initials="K." surname="Talaulikar" fullname="Ketan Talaulikar">
<organization>Cisco Systems, Inc.</organization> <organization>Cisco Systems, Inc.</organization>
<address> <address>
<postal> <postal>
<country>India</country> <country>India</country>
</postal> </postal>
<email>ketant.ietf@gmail.com</email> <email>ketant.ietf@gmail.com</email>
</address> </address>
</contact> </contact>
<contact initials="D." surname="Voyer" fullname="Daniel Voyer"> <contact initials="D." surname="Voyer" fullname="Daniel Voyer">
<organization>Bell Canada</organization> <organization>Bell Canada</organization>
<address> <address>
<postal> <postal>
<country>Canada</country> <country>Canada</country>
</postal> </postal>
<email>daniel.voyer@bell.ca</email> <email>daniel.voyer@bell.ca</email>
</address> </address>
</contact> </contact>
<contact initials="S." surname="Zadok" fullname="Shay Zadok"> <contact initials="S." surname="Zadok" fullname="Shay Zadok">
<organization>Broadcom</organization> <organization>Broadcom</organization>
<address> <address>
<postal> <postal>
<country>Israel</country> <country>Israel</country>
</postal> </postal>
<email>shay.zadok@broadcom.com</email> <email>shay.zadok@broadcom.com</email>
</address> </address>
</contact> </contact>
</section> </section>
</back> </back>
<!-- ##markdown-source: <!--[rfced] We had the following questions related to terminology used
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r5NhGAXwZZrgqQTjME9S+DOY+GG0442w65UY6KcRdplQjzYAEJqNklmcI8Bo pseudocode vs. pseudo code
NGM1e23vRRhlZ/A/taC9CKATjwLzm8KawmyUeIPrLA8msN2DeNQ21nL20wi/ upper-layer header vs. Upper-layer Header vs. Upper-Layer header
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GyUP214/BOCplR2GM/WJvaq/nu7D7U6nsGX8wDyFWdvHLj/9kRMo2qO47hSe
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z9KgiOzeYT42lvEPHKUdt8/FKD+dyV71kNiz7huRmxvftlE7WvCenbS9Ez/7 b) Is there another way to say "a ...SID of this document"? Later we
Y/ZBzXiSDIM015/a0x6dnnpHQY60GMAeJ5f0uTF1St1/Sql7G2hy9U5/aXun see "the SIDs introduced in this document". Might that work here and
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HB7sHewPLJDy196vcPlRnnyJwph3jAfB1KcIMMDkik57F36YZsZSe51er9Xt [RFC9514]).
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cT9QqkaBBaG00SlDaaMKShsMJegzadlwas2ycNxisFfAbL1zZ6DBEPeFWxt3 throughout the document:
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6Ld6nXa3Hq5+PPaO9/a9tyCMMFirgHaUfEARvQAsN+8EgMxwGtpXO8aeBLMs i) CSID is expanded as both "Compressed SRv6 Segment List Encoding
XSFusjJMkg/ZiljM/+l1xHLgN1gQ/BeWBP/FRcEPWpYFu9ZVmF8wesFi/NY0 (CSID)" (in the title) and "Compressed-SID (CSID)" (in the document
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