Internet DRAFT - draft-ietf-spring-srv6-srh-compression
draft-ietf-spring-srv6-srh-compression
SPRING W. Cheng, Ed.
Internet-Draft China Mobile
Intended status: Standards Track C. Filsfils
Expires: 1 September 2024 Cisco Systems, Inc.
Z. Li
Huawei Technologies
B. Decraene
Orange
F. Clad, Ed.
Cisco Systems, Inc.
29 February 2024
Compressed SRv6 Segment List Encoding
draft-ietf-spring-srv6-srh-compression-13
Abstract
Segment Routing over IPv6 (SRv6) is the instantiation of Segment
Routing (SR) on the IPv6 dataplane. This document specifies new
flavors for the SR segment endpoint 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.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 1 September 2024.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 5
3. Basic Concepts . . . . . . . . . . . . . . . . . . . . . . . 6
4. SR Segment Endpoint Flavors . . . . . . . . . . . . . . . . . 6
4.1. NEXT-C-SID Flavor . . . . . . . . . . . . . . . . . . . . 8
4.1.1. End with NEXT-C-SID . . . . . . . . . . . . . . . . . 9
4.1.2. End.X with NEXT-C-SID . . . . . . . . . . . . . . . . 10
4.1.3. End.T with NEXT-C-SID . . . . . . . . . . . . . . . . 11
4.1.4. End.B6.Encaps with NEXT-C-SID . . . . . . . . . . . . 11
4.1.5. End.B6.Encaps.Red with NEXT-C-SID . . . . . . . . . . 12
4.1.6. End.BM with NEXT-C-SID . . . . . . . . . . . . . . . 12
4.1.7. Combination with PSP, USP and USD flavors . . . . . . 13
4.2. REPLACE-C-SID Flavor . . . . . . . . . . . . . . . . . . 13
4.2.1. End with REPLACE-C-SID . . . . . . . . . . . . . . . 15
4.2.2. End.X with REPLACE-C-SID . . . . . . . . . . . . . . 17
4.2.3. End.T with REPLACE-C-SID . . . . . . . . . . . . . . 17
4.2.4. End.B6.Encaps with REPLACE-C-SID . . . . . . . . . . 18
4.2.5. End.B6.Encaps.Red with REPLACE-C-SID . . . . . . . . 18
4.2.6. End.BM with REPLACE-C-SID . . . . . . . . . . . . . . 19
4.2.7. End.DX and End.DT with REPLACE-C-SID . . . . . . . . 19
4.2.8. Combination with PSP, USP, and USD flavors . . . . . 20
5. C-SID Allocation . . . . . . . . . . . . . . . . . . . . . . 20
5.1. Global C-SID . . . . . . . . . . . . . . . . . . . . . . 21
5.2. Local C-SID . . . . . . . . . . . . . . . . . . . . . . . 21
5.3. GIB/LIB Usage . . . . . . . . . . . . . . . . . . . . . . 21
5.4. Recommended Installation of C-SIDs in FIB . . . . . . . . 22
6. SR Source Node . . . . . . . . . . . . . . . . . . . . . . . 24
6.1. Segment Validation for Compression . . . . . . . . . . . 24
6.2. Segment List Compression . . . . . . . . . . . . . . . . 24
6.3. Rules for segment lists containing NEXT-C-SID flavor
SIDs . . . . . . . . . . . . . . . . . . . . . . . . . . 28
6.4. Rules for segment lists containing REPLACE-C-SID flavor
SIDs . . . . . . . . . . . . . . . . . . . . . . . . . . 29
6.5. Upper-Layer Checksums . . . . . . . . . . . . . . . . . . 29
7. Inter-Domain Compression . . . . . . . . . . . . . . . . . . 30
7.1. End.PS: Prefix Swap . . . . . . . . . . . . . . . . . . . 30
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7.1.1. End.PS with NEXT-C-SID . . . . . . . . . . . . . . . 31
7.1.2. End.PS with REPLACE-C-SID . . . . . . . . . . . . . . 31
7.2. End.XPS: L3 Cross-Connect and Prefix Swap . . . . . . . . 31
7.2.1. End.XPS with NEXT-C-SID . . . . . . . . . . . . . . . 32
7.2.2. End.XPS with REPLACE-C-SID . . . . . . . . . . . . . 32
8. Control Plane . . . . . . . . . . . . . . . . . . . . . . . . 32
9. Operational Considerations . . . . . . . . . . . . . . . . . 34
9.1. Pinging a SID . . . . . . . . . . . . . . . . . . . . . . 34
9.2. ICMP Error Processing . . . . . . . . . . . . . . . . . . 35
10. Implementation Status . . . . . . . . . . . . . . . . . . . . 35
10.1. Cisco Systems . . . . . . . . . . . . . . . . . . . . . 36
10.2. Huawei Technologies . . . . . . . . . . . . . . . . . . 37
10.3. Nokia . . . . . . . . . . . . . . . . . . . . . . . . . 37
10.4. Arrcus . . . . . . . . . . . . . . . . . . . . . . . . . 38
10.5. Juniper Networks . . . . . . . . . . . . . . . . . . . . 38
10.6. Marvell . . . . . . . . . . . . . . . . . . . . . . . . 39
10.7. Broadcom . . . . . . . . . . . . . . . . . . . . . . . . 39
10.8. ZTE Corporation . . . . . . . . . . . . . . . . . . . . 40
10.9. New H3C Technologies . . . . . . . . . . . . . . . . . . 40
10.10. Ruijie Network . . . . . . . . . . . . . . . . . . . . . 40
10.11. Ciena . . . . . . . . . . . . . . . . . . . . . . . . . 41
10.12. Centec . . . . . . . . . . . . . . . . . . . . . . . . . 41
10.13. Open Source . . . . . . . . . . . . . . . . . . . . . . 41
10.14. Interoperability Reports . . . . . . . . . . . . . . . . 42
10.14.1. Bell Canada / Ciena 2023 . . . . . . . . . . . . . 42
10.14.2. EANTC 2023 . . . . . . . . . . . . . . . . . . . . 42
10.14.3. China Mobile 2020 . . . . . . . . . . . . . . . . . 42
11. Applicability to other SR Segment Endpoint Behaviors . . . . 44
12. Security Considerations . . . . . . . . . . . . . . . . . . . 44
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 45
13.1. SRv6 Endpoint Behaviors . . . . . . . . . . . . . . . . 45
14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 48
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 48
15.1. Normative References . . . . . . . . . . . . . . . . . . 48
15.2. Informative References . . . . . . . . . . . . . . . . . 49
Appendix A. Complete pseudocodes . . . . . . . . . . . . . . . . 53
A.1. End with NEXT-C-SID . . . . . . . . . . . . . . . . . . . 53
A.2. End.X with NEXT-C-SID . . . . . . . . . . . . . . . . . . 55
A.3. End.T with NEXT-C-SID . . . . . . . . . . . . . . . . . . 57
A.4. End.B6.Encaps with NEXT-C-SID . . . . . . . . . . . . . . 59
A.5. End.BM with NEXT-C-SID . . . . . . . . . . . . . . . . . 61
A.6. End with REPLACE-C-SID . . . . . . . . . . . . . . . . . 63
A.7. End.X with REPLACE-C-SID . . . . . . . . . . . . . . . . 65
A.8. End.T with REPLACE-C-SID . . . . . . . . . . . . . . . . 67
A.9. End.B6.Encaps with REPLACE-C-SID . . . . . . . . . . . . 69
A.10. End.BM with REPLACE-C-SID . . . . . . . . . . . . . . . . 70
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 72
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 73
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1. Introduction
The Segment Routing (SR) architecture [RFC8402] describes two data
plane instantiations of SR: SR over MPLS (SR-MPLS) and SR over IPv6
(SRv6).
SRv6 Network Programming [RFC8986] defines a framework to build a
network program with topological and service segments (also referred
to by their Segment Identifier (SID)) carried in a Segment Routing
Header (SRH) [RFC8754].
Some SRv6 applications such as strict path traffic engineering may
require long segment lists. Compressing the encoding of these long
segment lists in the packet header can significantly reduce the
header size. This document specifies new flavors to the SR segment
endpoint behaviors defined in [RFC8986] that enable a compressed
encoding of the SRv6 segment list.
The flavors defined in this document leverage the SRv6 data plane
defined in [RFC8754] and [RFC8986], and are compatible with the SRv6
control plane extensions for IS-IS [RFC9352], OSPF [RFC9513], and BGP
[RFC9252].
2. Terminology
This document leverages the terms defined in [RFC8402], [RFC8754],
and [RFC8986]. The reader is assumed to be familiar with this
terminology.
This document introduces the following new terms:
* Locator-Block: The most significant bits of a SID locator that
represent the SRv6 SID block. The Locator-Block is referred to as
"B" in Section 3.1 of [RFC8986].
* Locator-Node: The least significant bits of a SID locator that
identify the SR segment endpoint node instantiating the SID. The
Locator-Node is referred to as "N" in Section 3.1 of [RFC8986].
* Compressed-SID (C-SID): A compressed encoding of a SID. The C-SID
includes the Locator-Node and Function bits of the SID being
compressed.
* C-SID container: A 128-bit container holding a list of one or more
C-SIDs.
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* C-SID sequence: A group of one or more consecutive segment list
entries carrying the common Locator-Block and at least one C-SID
container.
* Uncompressed SID sequence: A group of one or more consecutive
uncompressed SIDs in a segment list.
* Compressed segment list encoding: A segment list encoding that
reduces the packet header length thanks to one or more C-SID
sequences. A compressed segment list encoding also contains zero,
one, or more uncompressed SID sequences.
* Global Identifiers Block (GIB): The pool of C-SID values available
for global allocation.
* Local Identifiers Block (LIB): The pool of C-SID values available
for local allocation.
In this document, the length of each constituent part of a SID is
referred to as follows.
* LBL is the Locator-Block length of the SID.
* LNL is the Locator-Node length of the SID.
* FL is the Function length of the SID.
* AL is the Argument length of the SID.
In addition, LNFL is the sum of the Locator-Node length and the
Function length of the SID. It is also referred to as the C-SID
length.
2.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
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3. Basic Concepts
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 padding bits.
The compressed segment list encoding is fully compatible with and
builds upon the mechanisms specified in [RFC8754] and [RFC8986]. The
compressed encoding is achieved by combining a compressed segment
list encoding logic on the SR source node (Section 6) with new
flavors of the base SRv6 segment endpoint behaviors that decode this
compressed encoding (Section 4).
A segment list can be encoded in the packet header using any
combination of compressed and uncompressed sequences. The C-SID
sequences leverage the flavors defined in this document, while the
uncompressed sequences use behaviors and flavors defined in other
documents, such as [RFC8986]. An SR source node constructs and
compresses the SID-list depending on the SIDs instantiated on each SR
segment endpoint node that the packet should traverse, as well as its
own compression capabilities.
The compressed segment list encoding works with any Locator-Block
allocation. 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 prefix allocated to SRv6 SIDs as
discussed in Section 5 of [I-D.ietf-6man-sids].
4. SR Segment Endpoint Flavors
This section defines two SR segment endpoint flavors, NEXT-C-SID and
REPLACE-C-SID, for the End, End.X, End.T, End.B6.Encaps,
End.B6.Encaps.Red, and End.BM behaviors of [RFC8986]. This section
also defines a REPLACE-C-SID flavor for the End.DX6, End.DX4,
End.DT6, End.DT4, End.DT46, End.DX2, End.DX2V, End.DT2U, and End.DT2M
behaviors of [RFC8986]. A counterpart NEXT-C-SID flavor is not
defined for these SIDs because they can be included within a C-SID
sequence that uses the NEXT-C-SID flavor without any modification of
the procedure defined in [RFC8986]. Future documents may extend the
applicability of the NEXT-C-SID and REPLACE-C-SID flavors to other SR
segment endpoint behaviors (see Section 11).
The use of these flavors, either individually or in combination,
enables the compressed segment list encoding.
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The NEXT-C-SID flavor and the REPLACE-C-SID flavor both leverage the
SID Argument to determine the next segment to be processed, but
employ different segment list compression schemes. With the NEXT-
C-SID flavor, each C-SID container is a fully formed SRv6 SID with
the common Locator-Block for all the C-SIDs in the C-SID container, a
Locator-Node and Function that are those of the first C-SID, and an
Argument carrying the subsequent C-SIDs. With the REPLACE-C-SID
flavor, only the first element in a C-SID sequence is a fully formed
SRv6 SID. It has the common Locator-Block for all the C-SIDs in the
C-SID sequence, and a Locator-Node and Function that are those of the
first C-SID. The remaining elements in the C-SID sequence are C-SID
containers carrying the subsequent C-SIDs without the Locator-Block.
SRv6 is intended for use in a variety of networks that require
different prefix lengths and SID numbering spaces. Each of the two
flavors introduced in this document comes with its own
recommendations for Locator-Block and C-SID length, as specified in
Section 4.1 and Section 4.2. These flavors are best suited for
different environments, depending on the requirements of the network.
For instance, larger C-SID lengths may be more suitable for networks
requiring ample SID numbering space, while smaller C-SID 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. Network
operators can choose the flavor that best suits their use case,
deployment design, and network scale.
The SIDs of both flavors can co-exist in the same SR domain, on the
same SR segment endpoint node, and even in the same segment list.
However, it is RECOMMENDED, for ease of operation, that a single
compressed encoding flavor be used in a given routing domain. In a
multi-domain deployment, different flavors may be used in different
routing domains of the SR domain.
In the remainder of this document, the term "a SID of this document"
refers to any End, End.X, End.T, End.B6.Encaps, End.B6.Encaps.Red, or
End.BM SID with the NEXT-C-SID or the REPLACE-C-SID flavor, and with
any combination of Penultimate Segment Pop (PSP), Ultimate Segment
Pop (USP), and Ultimate Segment Decapsulation (USD) flavor, or any
End.DX6, End.DX4, End.DT6, End.DT4, End.DT46, End.DX2, End.DX2V,
End.DT2U, or End.DT2M with the REPLACE-C-SID flavor. All the SIDs
introduced in this document are listed in Table 1.
In the remainder of this document, the terms "NEXT-C-SID flavor SID"
and "REPLACE-C-SID flavor SID" refer to any SID of this document with
the NEXT-C-SID flavor and with the REPLACE-C-SID flavor,
respectively.
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4.1. NEXT-C-SID Flavor
A C-SID sequence using the NEXT-C-SID flavor comprises one or more
C-SID containers. Each C-SID container is a fully formed 128-bit SID
structured as shown in Figure 1. It carries a Locator-Block followed
by a series of C-SIDs. The Locator-Node and Function of the C-SID
container are those of the first C-SID, and its Argument is the
contiguous series of subsequent C-SIDs. The second C-SID is encoded
in the most significant bits of the C-SID container Argument, the
third C-SID is encoded in the bits of the Argument that immediately
follow the second C-SID, and so on. When all C-SIDs have the same
length, a C-SID container can carry up to K C-SIDs, where K is
computed as floor((128-LBL)/LNFL) (floor(x) is the greatest integer
less than or equal to x [GKP94]). Each C-SID container for NEXT-
C-SID is independent, such that contiguous C-SID containers in a
C-SID sequence can be considered as separate C-SID sequences.
When a C-SID sequence comprises at least two C-SIDs, the last C-SID
in the sequence is not required to have the NEXT-C-SID flavor. It
can be bound to any behavior and flavor(s), including the REPLACE-
C-SID flavor, as long as the updated destination address resulting
from the processing of the previous C-SID in the sequence is a valid
form for that last SID. Line S12 of the first pseudocode in
Section 6.2 provides sufficient conditions to ensure this property.
+------------------------------------------------------------------+
| Locator-Block |Loc-Node| Argument |
| |Function| |
+------------------------------------------------------------------+
<-------- LBL ---------> < LNFL > <------------- AL ------------->
Figure 1: Structure of a NEXT-C-SID flavor SID (scaled for a
48-bit Locator- Block, 16-bit combined Locator-Node and Function,
and 64-bit Argument)
An implementation MUST support a 32-bit Locator-Block length (LBL)
and a 16-bit C-SID length (LNFL) for NEXT-C-SID flavor SIDs, and may
support any other Locator-Block and C-SID length. A deployment
SHOULD use a consistent Locator-Block length and C-SID length for all
SIDs of the SR domain.
The Argument length (AL) for NEXT-C-SID flavor SIDs is equal to 128-
LBL-LNFL.
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When processing an IPv6 packet that matches a FIB entry locally
instantiated as a SID with the NEXT-C-SID flavor, the SR segment
endpoint node applies the procedure specified in the following
subsection that corresponds to the SID behavior. If the SID also has
the PSP, USP, or USD flavor, the procedure is modified as described
in Section 4.1.7.
An SR segment endpoint node instantiating a SID with the NEXT-C-SID
flavor MUST accept any Argument value for that SID.
At high level, for any SID with the NEXT-C-SID flavor, the SR segment
endpoint node determines the next SID of the SID list as follows. If
the Argument value of the active SID is non-zero, the SR segment
endpoint node constructs the next SID from the active SID by copying
the entire SID Argument value to the bits that immediately follow the
Locator-Block, thus overwriting the active SID Locator-Node and
Function with those of the next C-SID, and filling the least
significant LNFL bits of the Argument with zeros. Otherwise (if the
Argument value is 0), the SR segment endpoint node copies the next
128-bit Segment List entry from the SRH to the Destination Address
field of the IPv6 header.
4.1.1. End with NEXT-C-SID
When processing an IPv6 packet that matches a FIB entry locally
instantiated as an End SID with the NEXT-C-SID flavor, the procedure
described in Section 4.1 of [RFC8986] is executed with the following
modifications.
The below pseudocode is inserted between lines S01 and S02 of the SRH
processing in Section 4.1 of [RFC8986]. In addition, this pseudocode
is executed before processing any extension header that is not an
SRH, a Hop-by-Hop header or a Destination Option header, or before
processing the upper-layer header, whichever comes first.
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N01. If (DA.Argument != 0) {
N02. If (IPv6 Hop Limit <= 1) {
N03. Send an ICMP Time Exceeded message to the Source Address,
Code 0 (Hop limit exceeded in transit),
interrupt packet processing and discard the packet.
N04. }
N05. Copy DA.Argument into the bits [LBL..(LBL+AL-1)] of the
Destination Address.
N06. Set the bits [(LBL+AL)..127] of the Destination Address to
zero.
N07. Decrement IPv6 Hop Limit by 1.
N08. Submit the packet to the egress IPv6 FIB lookup for
transmission to the next destination.
N09. }
| Notes:
|
| * DA.Argument identifies the value contained in the bits
| [(LBL+LNFL)..127] in the Destination Address of the IPv6
| header.
|
| * The value in the Segments Left field of the SRH is not
| modified when DA.Argument in the received packet has a
| non-zero value.
A rendering of the complete pseudocode is provided in Appendix A.1.
4.1.2. End.X with NEXT-C-SID
When processing an IPv6 packet that matches a FIB entry locally
instantiated as an End.X SID with the NEXT-C-SID flavor, the
procedure described in Section 4.2 of [RFC8986] is executed with the
following modifications.
The pseudocode in Section 4.1.1 of this document is modified by
replacing line N08 as shown below.
N08. Submit the packet to the IPv6 module for transmission to the
new destination via a member of J.
| Note: the variable J is defined in Section 4.2 of [RFC8986].
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The resulting pseudocode is inserted between lines S01 and S02 of the
SRH processing in Section 4.1 of [RFC8986] after applying the
modification described in Section 4.2 of [RFC8986]. In addition,
this pseudocode is executed before processing any extension header
that is not an SRH, a Hop-by-Hop header or a Destination Option
header, or before processing the upper-layer header, whichever comes
first.
A rendering of the complete pseudocode is provided in Appendix A.2.
4.1.3. End.T with NEXT-C-SID
When processing an IPv6 packet that matches a FIB entry locally
instantiated as an End.T SID with the NEXT-C-SID flavor, the
procedure described in Section 4.3 of [RFC8986] is executed with the
following modifications.
The pseudocode in Section 4.1.1 of this document is modified by
replacing line N08 as shown below.
N08.1. Set the packet's associated FIB table to T.
N08.2. Submit the packet to the egress IPv6 FIB lookup for
transmission to the new destination.
| Note: the variable T is defined in Section 4.3 of [RFC8986].
The resulting pseudocode is inserted between lines S01 and S02 of the
SRH processing in Section 4.1 of [RFC8986] after applying the
modification described in Section 4.3 of [RFC8986]. In addition,
this pseudocode is executed before processing any extension header
that is not an SRH, a Hop-by-Hop header or a Destination Option
header, or before processing the upper-layer header, whichever comes
first.
A rendering of the complete pseudocode is provided in Appendix A.3.
4.1.4. End.B6.Encaps with NEXT-C-SID
When processing an IPv6 packet that matches a FIB entry locally
instantiated as an End.B6.Encaps SID with the NEXT-C-SID flavor, the
procedure described in Section 4.13 of [RFC8986] is executed with the
following modifications.
The pseudocode in Section 4.1.1 of this document is modified by
replacing line N08 as shown below.
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N08.1. Push a new IPv6 header with its own SRH containing B.
N08.2. Set the outer IPv6 SA to A.
N08.3. Set the outer IPv6 DA to the first SID of B.
N08.4. Set the outer Payload Length, Traffic Class, Flow Label,
Hop Limit, and Next Header fields.
N08.5. Submit the packet to the egress IPv6 FIB lookup for
transmission to the next destination.
| Note: the variables A and B, as well as the values of the
| Payload Length, Traffic Class, Flow Label, Hop Limit, and Next
| Header are defined in Section 4.13 of [RFC8986].
The resulting pseudocode is inserted between lines S01 and S02 of the
SRH processing in Section 4.13 of [RFC8986]. In addition, this
pseudocode is executed before processing any extension header that is
not an SRH, a Hop-by-Hop header or a Destination Option header, or
before processing the upper-layer header, whichever comes first.
A rendering of the complete pseudocode is provided in Appendix A.4.
Similar to the base End.B6.Encaps SID defined in Section 4.13 of
[RFC8986], the NEXT-C-SID flavor variant updates the Destination
Address field of the inner IPv6 header to the next SID in the
original segment list before encapsulating the packet with the
segment list of SR Policy B. At the endpoint of SR Policy B, the
encapsulation is removed and the inner packet is forwarded towards
the exposed destination address, which already contains the next SID
in the original segment list.
4.1.5. End.B6.Encaps.Red with NEXT-C-SID
When processing an IPv6 packet that matches a FIB entry locally
instantiated as an End.B6.Encaps.Red SID with the NEXT-C-SID flavor,
the procedure described in Section 4.14 of [RFC8986] is executed with
the same modifications as in Section 4.1.4 of this document.
4.1.6. End.BM with NEXT-C-SID
When processing an IPv6 packet that matches a FIB entry locally
instantiated as an End.BM SID with the NEXT-C-SID flavor, the
procedure described in Section 4.15 of [RFC8986] is executed with the
following modifications.
The pseudocode in Section 4.1.1 of this document is modified by
replacing line N08 as shown below.
N08.1. Push the MPLS label stack for B.
N08.2. Submit the packet to the MPLS engine for transmission.
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| Note: the variable B is defined in Section 4.15 of [RFC8986].
The resulting pseudocode is inserted between lines S01 and S02 of the
SRH processing in Section 4.15 of [RFC8986]. In addition, this
pseudocode is executed before processing any extension header that is
not an SRH, a Hop-by-Hop header or a Destination Option header, or
before processing the upper-layer header, whichever comes first.
A rendering of the complete pseudocode is provided in Appendix A.5.
4.1.7. Combination with PSP, USP and USD flavors
PSP: The PSP flavor defined in Section 4.16.1 of [RFC8986] is
unchanged when combined with the NEXT-C-SID flavor.
USP: The USP flavor defined in Section 4.16.2 of [RFC8986] is
unchanged when combined with the NEXT-C-SID flavor.
USD: The USP flavor defined in Section 4.16.3 of [RFC8986] is
unchanged when combined with the NEXT-C-SID flavor.
4.2. REPLACE-C-SID Flavor
A C-SID sequence using the REPLACE-C-SID flavor starts with a C-SID
container in fully formed 128-bit SID format. The Locator-Block of
this SID is the common Locator-Block for all the C-SIDs in the C-SID
sequence, its Locator-Node and Function are those of the first C-SID,
and its Argument carries the index of the current C-SID in the
current C-SID container. The Argument value is initially 0. When
more segments are present in the segment list, the C-SID sequence
continues with one or more C-SID containers in packed format carrying
the subsequent C-SIDs in the sequence. Each container in packed
format is a 128-bit Segment List entry split into K "positions" of
LNFL bits, where K is computed as floor(128/LNFL). If LNFL does not
divide into 128 perfectly, a zero pad is added in the least
significant bits of the C-SID container to fill the bits left over.
The second C-SID in the C-SID sequence is encoded in the least
significant bit position of the first C-SID container in packed
format (position K-1), the third C-SID is encoded in position K-2,
and so on.
The last C-SID in the C-SID sequence is not required to have the
REPLACE-C-SID flavor. It can be bound to any behavior and flavor(s),
including the NEXT-C-SID flavor, as long as it meets the conditions
defined in Section 6.
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The structure of a SID with the REPLACE-C-SID flavor is shown in
Figure 2. The same structure is also that of the C-SID container for
REPLACE-C-SID in fully formed 128-bit SID format.
+-------------------------------------------------------------------+
| Locator-Block | Locator-Node | Argument |
| | + Function | |
+-------------------------------------------------------------------+
<-------- LBL ---------> <---- LNFL ----> <--------- AL ---------->
Figure 2: Structure of a REPLACE-C-SID flavor SID (scaled for a
48-bit Locator- Block, 32-bit combined Locator-Node and Function,
and 48-bit Argument)
The structure of a C-SID container for REPLACE-C-SID in packed format
is shown in Figure 3.
+-------------------------------------------------------------------+
| Fourth C-SID | Third C-SID | Second C-SID | First C-SID |
| (position 0) | (position 1) | (position 2) | (position 3) |
+-------------------------------------------------------------------+
<---- LNFL ----> <---- LNFL ----> <---- LNFL ----> <---- LNFL ---->
Figure 3: Structure of a C-SID container for REPLACE-C-SID using
a 32-bit C-SID length (K = 4)
The REPLACE-C-SID flavor SIDs support any Locator-Block length (LBL),
depending on the needs of the operator, as long as it does not exceed
128-LNFL-ceiling(log_2(128/LNFL)) (ceiling(x) is the least integer
greater than or equal to x [GKP94]), so that enough bits remain
available for the C-SID and Argument. A Locator-Block length of 48,
56, 64, 72, or 80 bits is RECOMMENDED for address planning reasons.
This document defines the REPLACE-C-SID flavor for 16-bit and 32-bit
C-SID lengths (LNFL). An implementation MUST support a 32-bit C-SID
length for REPLACE-C-SID flavor SIDs.
A deployment SHOULD use a consistent Locator-Block length and C-SID
length for all SIDs of the SR domain.
The Argument length (AL) for REPLACE-C-SID flavor SIDs is equal to
128-LBL-LNFL. The index value is encoded in the least significant X
bits of the Argument, where X is computed as ceiling(log_2(128/
LNFL)).
When processing an IPv6 packet that matches a FIB entry locally
instantiated as a SID with the REPLACE-C-SID flavor, the SR segment
endpoint node applies the procedure specified in the following
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subsection that corresponds to the SID behavior. If the SID also has
the PSP, USP, or USD flavor, the procedure is modified as described
in Section 4.2.8.
At high level, at the start of a C-SID sequence using the REPLACE-
C-SID flavor, the first C-SID container in fully formed 128-bit SID
format is copied to the Destination Address of the IPv6 header.
Then, for any SID with the REPLACE-C-SID flavor, the SR segment
endpoint node determines the next SID of the SID list as follows.
When an SRH is present, the SR segment endpoint node decrements the
index value in the Argument of the active SID if the index value is
not 0 or, if it is 0, decrements the Segments Left value in the SRH
and sets the index value in the Argument of the active SID to K-1.
The updated index value indicates the position of the next C-SID
within the C-SID container in packed format at the "Segment List"
index "Segments Left" in the SRH. The SR segment endpoint node then
constructs the next SID by copying this next C-SID to the bits that
immediately follow the Locator-Block in the Destination Address field
of the IPv6 header, thus overwriting the active SID Locator-Node and
Function with those of the next C-SID. If no SRH is present, the SR
segment endpoint node ignores the index value in the SID Argument
(except End.DT2M, see Section 4.2.7) and processes the upper-layer
header as per [RFC8986]. The C-SID sequence ends with a last C-SID
in the last C-SID container that does not have the REPLACE-C-SID
flavor, or with the special C-SID value 0, or when reaching the end
of the segment list, whichever comes first.
4.2.1. End with REPLACE-C-SID
When processing an IPv6 packet that matches a FIB entry locally
instantiated as an End SID with the REPLACE-C-SID flavor, the SRH
processing described in Section 4.1 of [RFC8986] is executed with the
following modifications.
Line S02 of SRH processing in Section 4.1 of [RFC8986] is replaced as
follows.
S02. If (Segments Left == 0 and (DA.Arg.Index == 0 or
Segment List[0][DA.Arg.Index-1] == 0)) {
Lines S09 to S15 are replaced by the following pseudo code.
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R01. If (DA.Arg.Index != 0) {
R02. If ((Last Entry > max_LE) or (Segments Left > Last Entry)) {
R03. Send an ICMP Parameter Problem to the Source Address,
Code 0 (Erroneous header field encountered),
Pointer set to the Segments Left field,
interrupt packet processing and discard the packet.
R04. }
R05. Decrement DA.Arg.Index by 1.
R06. If (Segment List[Segments Left][DA.Arg.Index] == 0) {
R07. Decrement Segments Left by 1.
R08. Decrement IPv6 Hop Limit by 1.
R09. Update IPv6 DA with Segment List[Segments Left]
R10. Submit the packet to the egress IPv6 FIB lookup for
transmission to the new destination.
R11. }
R12. } Else {
R13. If((Last Entry > max_LE) or (Segments Left > Last Entry+1)){
R14. Send an ICMP Parameter Problem to the Source Address,
Code 0 (Erroneous header field encountered),
Pointer set to the Segments Left field,
interrupt packet processing and discard the packet.
R15. }
R16. Decrement Segments Left by 1.
R17. Set DA.Arg.Index to (floor(128/LNFL) - 1).
R18. }
R19. Decrement IPv6 Hop Limit by 1.
R20. Write Segment List[Segments Left][DA.Arg.Index] into the bits
[LBL..LBL+LNFL-1] of the Destination Address of the IPv6
header.
R21. Submit the packet to the egress IPv6 FIB lookup for
transmission to the new destination.
| Notes:
|
| * DA.Arg.Index identifies the value contained in the bits
| [(128-ceiling(log_2(128/LNFL)))..127] in the Destination
| Address of the IPv6 header.
|
| * Segment List[Segments Left][DA.Arg.Index] identifies the
| value contained in the bits
| [DA.Arg.Index*LNFL..(DA.Arg.Index+1)*LNFL-1] in the SRH
| Segment List entry at index Segments Left.
The upper-layer header processing described in Section 4.1.1 of
[RFC8986] is unchanged.
A rendering of the complete pseudocode is provided in Appendix A.6.
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4.2.2. End.X with REPLACE-C-SID
When processing an IPv6 packet that matches a FIB entry locally
instantiated as an End.X SID with the REPLACE-C-SID flavor, the
procedure described in Section 4.2 of [RFC8986] is executed with the
following modifications.
The pseudocode in Section 4.2.1 of this document is modified by
replacing lines R10 and R21 as shown below.
R10. Submit the packet to the IPv6 module for transmission to the
new destination via a member of J.
R21. Submit the packet to the IPv6 module for transmission to the
new destination via a member of J.
| Note: the variable J is defined in Section 4.2 of [RFC8986].
The SRH processing in Section 4.2 of [RFC8986] is replaced with the
resulting pseudocode. The upper-layer header processing is
unchanged.
A rendering of the complete pseudocode is provided in Appendix A.7.
4.2.3. End.T with REPLACE-C-SID
When processing an IPv6 packet that matches a FIB entry locally
instantiated as an End.T SID with the REPLACE-C-SID flavor, the
procedure described in Section 4.3 of [RFC8986] is executed with the
following modifications.
The pseudocode in Section 4.2.1 of this document is modified by
replacing lines R10 and R21 as shown below.
R10.1. Set the packet's associated FIB table to T.
R10.2. Submit the packet to the egress IPv6 FIB lookup for
transmission to the new destination.
R21.1. Set the packet's associated FIB table to T.
R21.2. Submit the packet to the egress IPv6 FIB lookup for
transmission to the new destination.
| Note: the variable T is defined in Section 4.3 of [RFC8986].
The SRH processing in Section 4.3 of [RFC8986] is replaced with the
resulting pseudocode. The upper-layer header processing is
unchanged.
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A rendering of the complete pseudocode is provided in Appendix A.8.
4.2.4. End.B6.Encaps with REPLACE-C-SID
When processing an IPv6 packet that matches a FIB entry locally
instantiated as an End.B6.Encaps SID with the REPLACE-C-SID flavor,
the procedure described in Section 4.13 of [RFC8986] is executed with
the following modifications.
The pseudocode in Section 4.2.1 of this document is modified by
replacing lines R10 and R21 as shown below.
R10.1. Push a new IPv6 header with its own SRH containing B.
R10.2. Set the outer IPv6 SA to A.
R10.3. Set the outer IPv6 DA to the first SID of B.
R10.4. Set the outer Payload Length, Traffic Class, Flow Label,
Hop Limit, and Next Header fields.
R10.5. Submit the packet to the egress IPv6 FIB lookup for
transmission to the next destination.
R21.1. Push a new IPv6 header with its own SRH containing B.
R21.2. Set the outer IPv6 SA to A.
R21.3. Set the outer IPv6 DA to the first SID of B.
R21.4. Set the outer Payload Length, Traffic Class, Flow Label,
Hop Limit, and Next Header fields.
R21.5. Submit the packet to the egress IPv6 FIB lookup for
transmission to the next destination.
| Note: the variables A and B, as well as the values of the
| Payload Length, Traffic Class, Flow Label, Hop Limit, and Next
| Header are defined in Section 4.13 of [RFC8986].
The SRH processing in Section 4.13 of [RFC8986] is replaced with the
resulting pseudocode. The upper-layer header processing is
unchanged.
A rendering of the complete pseudocode is provided in Appendix A.9.
4.2.5. End.B6.Encaps.Red with REPLACE-C-SID
When processing an IPv6 packet that matches a FIB entry locally
instantiated as an End.B6.Encaps.Red SID with the REPLACE-C-SID
flavor, the procedure described in Section 4.14 of [RFC8986] is
executed with the same modifications as in Section 4.2.4 of this
document.
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4.2.6. End.BM with REPLACE-C-SID
When processing an IPv6 packet that matches a FIB entry locally
instantiated as an End.BM SID with the REPLACE-C-SID flavor, the
procedure described in Section 4.15 of [RFC8986] is executed with the
following modifications.
The pseudocode in Section 4.2.1 of this document is modified by
replacing lines R10 and R21 as shown below.
R10.1. Push the MPLS label stack for B.
R10.2. Submit the packet to the MPLS engine for transmission.
R21.1. Push the MPLS label stack for B.
R21.2. Submit the packet to the MPLS engine for transmission.
| Note: the variable B is defined in Section 4.15 of [RFC8986].
The SRH processing in Section 4.15 of [RFC8986] is replaced with the
resulting pseudocode. The upper-layer header processing is
unchanged.
A rendering of the complete pseudocode is provided in Appendix A.10.
4.2.7. End.DX and End.DT with REPLACE-C-SID
When processing an IPv6 packet that matches a FIB entry locally
instantiated as an End.DX6, End.DX4, End.DT6, End.DT4, End.DT46,
End.DX2, End.DX2V, or End.DT2U SID with the REPLACE-C-SID flavor, the
corresponding procedure described in Sections 4.4 through 4.11 of
[RFC8986] is executed.
These SIDs differ from those defined in [RFC8986] by the presence of
an Argument as part of the SID structure. The Argument value is
ignored by the SR segment endpoint node.
When processing an IPv6 packet that matches a FIB entry locally
instantiated as an End.DT2M SID with the REPLACE-C-SID flavor, the
procedure described in Section 4.12 of [RFC8986] is executed with the
following modification.
The value of Arg.FE2 is 16-bit long. The SR segment endpoint node
obtains the value Arg.FE2 from the 16 most significant bits of
DA.Argument if DA.Arg.Index is zero, or from the 16 least significant
bits of the next position in the current C-SID container (Segment
List[Segments Left][DA.Arg.Index-1]) otherwise (DA.Arg.Index is non-
zero).
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4.2.8. Combination with PSP, USP, and USD flavors
PSP: When combined with the REPLACE-C-SID flavor, the additional PSP
flavor instructions defined in Section 4.16.1.2 of [RFC8986] are
inserted after lines R09 and R20 of the pseudocode in Section 4.2.1,
and the first line of the inserted instructions after R20 is modified
as follows.
R20.1. If (Segments Left == 0 and (DA.Arg.Index == 0 or
Segment List[0][DA.Arg.Index-1] == 0)) {
| Note: Segment List[Segments Left][DA.Arg.Index-1] identifies
| the value contained in the bits [(DA.Arg.Index-
| 1)*LNFL..DA.Arg.Index*LNFL-1] in the SRH Segment List entry at
| index Segments Left.
USP: When combined with the REPLACE-C-SID flavor, the line S03 of the
pseudocode in Section 4.2.1 are substituted by the USP flavor
instructions S03.1 to S03.4 defined in Section 4.16.2 of [RFC8986].
Note that S03 is shown in the complete pseudocode in Appendix A.6.
USD: The USD flavor defined in Section 4.16.3 of [RFC8986] is
unchanged when combined with the REPLACE-C-SID flavor.
5. C-SID Allocation
The C-SID value of 0 is reserved. It is used to indicate the end of
a C-SID container.
In order to efficiently manage the C-SID numbering space, a
deployment may divide it into two non-overlapping sub-spaces: a
Global Identifiers Block (GIB) and a Local Identifiers Block (LIB).
The C-SID 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 semantic on an SR segment endpoint node and
within the scope of the Locator-Block.
The concept of LIB is applicable to SRv6 and specifically to its
NEXT-C-SID and REPLACE-C-SID flavors. The shorter the C-SID, the
more benefit the LIB brings.
The opportunity to use these sub-spaces, their size, and their C-SID
allocation policy depends on the C-SID length relative to the size of
the network (e.g., number of nodes, links, service routes). Some
guidelines for a typical deployment scenario are provided in the
below subsections.
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5.1. Global C-SID
A global C-SID is a C-SID allocated from the GIB.
A global C-SID identifies a segment defined at the Locator-Block
level. The tuple (Locator-Block, C-SID) identifies the same segment
across all nodes of the SR domain. A typical example is a prefix
segment bound to the End behavior.
A node can have multiple global C-SIDs under the same Locator-Block
(e.g., one per IGP flexible algorithm ([RFC9350])). Multiple nodes
may share the same global C-SID (e.g., anycast).
5.2. Local C-SID
A local C-SID is a C-SID allocated from the LIB.
A local C-SID identifies a segment defined at the node level and
within the scope of a particular Locator-Block. The tuple (Locator-
Block, C-SID) identifies 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.
Let N1 and N2 be two different physical nodes of the SR domain and I
a local C-SID value, N1 may allocate value I to SID S1 and N2 may
allocate the same value I to SID S2.
5.3. GIB/LIB Usage
GIB and LIB usage is a local implementation and/or configuration
decision, however, some guidelines for determining usage for specific
SID behaviors and recommendations are provided.
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 global segments, such as SIDs
that identify a node.
The LIB number space is unique per node. Each node is able to fully
utilize the entire LIB number space without consideration of
assignments at other nodes. Therefore its use is prioritized for
local segments, such as SIDs that identify services (of which there
may be many) at nodes, cross-connects, or adjacencies.
While a longer C-SID length permits more flexibility in which SID
behaviors may be assigned from the GIB, it also reduces the
compression efficiency.
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Given the previous Locator-Block and C-SID length recommendations,
the following GIB/LIB usage is recommended:
* NEXT-C-SID:
- GIB: End
- 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
* REPLACE-C-SID:
- GIB: End, End.X, End.T, End.DT4/6/46/2U/2M, End.DX4/6/2/2V,
End.B6.Encaps, End.B6.Encaps.Red, End.BM
- LIB: End.DX2/2V for large-scale pseudowire
Any other allocation is possible but may lead to a suboptimal use of
the C-SID numbering space.
5.4. Recommended Installation of C-SIDs in FIB
Section 4.3 of [RFC8754] defines how an SR segment endpoint node
identifies a locally instantiated SRv6 SID. To ensure that any valid
argument value is accepted, an SR segment endpoint node instantiating
a NEXT-C-SID or REPLACE-C-SID 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 + LNL + FL).
In addition, an SR segment endpoint node instantiating NEXT-C-SID
flavor SIDs from both GIB and LIB may install combined "Global +
Local" FIB entries to match a sequence of global and local C-SIDs in
a single longest prefix match (LPM) lookup.
For example, let us consider an SR segment endpoint node 10
instantiating the following two NEXT-C-SID flavor SIDs according to
the C-SID length, Locator-Block length, and GIB/LIB recommendations
in this section.
* 2001:db8:b1:10:: bound to the End behavior with the NEXT-C-SID
flavor is instantiated from GIB with
- Locator-Block length (LBL) = 48 (Locator-Block value
0x20010db800b1),
- Locator-Node length (LNL) = 16 (Locator-Node value 0x0010),
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- Function length (FL) = 0, and
- Argument length (AL) = 64.
* 2001:db8:b1:f123:: bound to the End.X behavior for its local IGP
adjacency 123 with the NEXT-C-SID flavor is instantiated from LIB
with
- Locator-Block length (LBL) = 48 (Locator-Block value
0x20010db800b1),
- Locator-Node length (LNL) = 0,
- Function length (FL) = 16 (Function value 0xf123), and
- Argument length (AL) = 64.
For SID 2001:db8:b1:10::, Node 10 would install the FIB entry
2001:db8:b1:10::/64 bound the End SID with the NEXT-C-SID flavor.
For SID 2001:db8:b1:f123::, Node 10 would install the FIB entry
2001:db8:b1:f123::/64 bound the End.X SID for adjacency 123 with the
NEXT-C-SID flavor.
In addition, Node 10 may also install the combined FIB entry
2001:db8:b1:10:f123::/80 bound the End.X SID for adjacency 123 with
the NEXT-C-SID flavor.
As another example, let us consider an SR segment endpoint node 20
instantiating the following two REPLACE-C-SID flavor SIDs according
to the C-SID length, Locator-Block length, and GIB/LIB
recommendations in this section.
* 2001:db8:b2:20:1:: 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 behavior with the
REPLACE-C-SID flavor.
* 2001:db8:b2:20:123:: 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 123 with the REPLACE-C-SID flavor.
For SID 2001:db8:b2:20:1::, Node 20 would install the FIB entry
2001:db8:b2:20:1::/80 bound the End SID with the REPLACE-C-SID
flavor.
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For SID 2001:db8:b2:20:123::, Node 20 would install the FIB entry
2001:db8:b2:20:123::/80 bound the End.X SID for adjacency 123 with
the REPLACE-C-SID flavor.
6. SR Source Node
An SR source node may learn from a control plane protocol (see
Section 8) or local configuration the SIDs that it can use in a
segment list, along with their respective SR segment endpoint
behavior, flavors, structure, and any other relevant attribute (e.g.,
the set of L3 adjacencies associated with an End.X SID).
6.1. Segment Validation for Compression
As part of the compression process or as a preliminary step, the SR
source node MUST validate the SID structure, if known, of each SID of
this document 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 controller (e.g., via BGP
[I-D.ietf-idr-segment-routing-te-policy] or PCEP
[I-D.ietf-pce-segment-routing-ipv6]).
A SID structure is valid for compression if it meets all the
following conditions.
* The Locator-Block length is not 0.
* The sum of the Locator-Node length and Function length is not 0.
* The Argument length is equal to 128-LBL-LNL-FL.
When compressing a segment list, the SR source node MUST treat an
invalid SID structure as unknown, and treats the SID as
incompressible.
Section 8 discusses how the SIDs of this document and their structure
can be advertised to the SR source node through various control plane
protocols.
6.2. Segment List Compression
An SR source node MAY compress a segment list when it includes NEXT-
C-SID and/or REPLACE-C-SID flavor SIDs in order to reduce the packet
header length.
It is out of the scope of this document to describe the mechanism
through which an uncompressed segment list is derived. As a general
guidance for implementation or future specification, such a mechanism
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should aim to select the combination of SIDs that would result in the
shortest compressed segment list. For example, by selecting a C-SID
flavor SID over an equivalent non-C-SID flavor SID or by consistently
selecting SIDs of the same C-SID flavor within each routing domain.
The segment list that the SR source node pushes onto the packet MUST
comply with the rules in Section 6.3 and Section 6.4 and result in
the same forwarding path as the original segment list.
If an SR source node chooses to compress the segment list, one method
is described below for illustrative purposes. Any other method
producing a compressed segment list of equal or shorter length than
the uncompressed segment list is compliant.
This method walks the uncompressed segment list and compresses each
series of consecutive NEXT-C-SID flavor SIDs and each series of
consecutive REPLACE-C-SID flavor SIDs.
* When the compression method encounters a series of one or more
consecutive compressible NEXT-C-SID flavor SIDs, it compresses the
series as follows. A SID with the NEXT-C-SID flavor is
compressible if its structure is known to the SR source node and
its Argument value is 0.
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S01. Initialize a C-SID container equal to the first SID in the
series, and initialize the remaining capacity of the C-SID
container to the AL of that SID
S02. For each subsequent SID in the series {
S03. If the current SID Locator-Block matches that of the C-SID
container and the current SID LNFL is lower than or equal to
the remaining capacity of the C-SID container {
S04. Copy the current SID Locator-Node and Function to the most
significant remaining Argument bits of the C-SID container
and decrement the remaining capacity by LNFL
S05. } Else {
S06. Push the C-SID container onto the compressed segment list
S07. Initialize a new C-SID container equal to the current SID in
the series, and initialize the remaining capacity of the
C-SID container to the AL of that SID
S08. } // End If
S09. } // End For
S10. If at least one SID remains in the uncompressed segment list
(following the series of compressible NEXT-C-SID flavor SIDs){
S11. Set S to the next SID in the uncompressed segment list
S12. If S is advertised with a SID structure, and the Locator-Block
of S matches that of the C-SID container, and the sum of the
Locator-Node, Function, and Argument length of S is lower
than or equal to the remaining capacity of the C-SID
container {
S13. Copy the Locator-Node, Function, and Argument of S to the
most significant remaining Argument bits of the C-SID
container
S14. } // End If
S15. } // End If
S16. Push the C-SID container onto the compressed segment list
* When the compression method encounters a series of REPLACE-C-SID
flavor SIDs of the same C-SID length in the uncompressed segment
list, it compresses the series as per the following high-level
pseudo code. A compression checking function ComCheck(F, S) is
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 value 0. If the check passes, then ComCheck(F,S)
returns true.
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S01. Initialize the first C-SID container in full SID format equal to
the first SID in the series
S02. Initialize the second C-SID container in packed format if there
are more than one SIDs, and initialize the remaining capacity
of the C-SID container to 128 bits
S03. For each subsequent SID in the uncompressed segment list {
S04. Set S to the current SID in the uncompressed segment list
S05. If ComCheck(First SID, S) {
S06. If the LNFL of S is lower than or equal to
the remaining capacity of the C-SID container {
S07. Copy the Locator-Node and Function of S to the least
significant remaining bits of the C-SID container
and decrement the remaining capacity by LNFL // Note
S08. } Else {
S09. Push the C-SID container onto the compressed segment list
S10. Initialize a new C-SID container in packed format with all
bits set to 0
S11 Copy the Locator-Node and Function of S to the least
significant remaining bits of the C-SID container
and decrement the remaining capacity by LNFL // Note
S12. }
S13. If S is not a REPLACE-C-SID flavor SID, then break
S14. } Else {
S15. Break
S16. } // End If
S17. } // End For
S18. Push the C-SID container (if it is not empty) onto the
compressed segment list
| Note: When the last C-SID is an End.DT2M SID with the REPLACE-
| C-SID flavor, if there is 0 or at least two C-SID positions
| left in the current C-SID container, the C-SID is encoded as
| described above and the value of the Arg.FE2 argument is placed
| in the 16 least significant bits of the next C-SID position.
| Otherwise (if there is only one C-SID position left in the
| current C-SID container), the current C-SID container is pushed
| onto the segment list (the value of the C-SID position 0
| remains zero) and the End.DT2M SID with the REPLACE-C-SID
| flavor is encoded in full SID format with the value of the
| Arg.FE2 argument in the 16 most significant bits of the SID
| Argument.
* In all remaining cases (i.e., when the compression method
encounters a SID in the uncompressed segment list that is not
handled by any of the previous subroutines), it pushes this SID as
is onto the compressed segment list.
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Regardless of how a compressed segment list is produced, the SR
source node writes it in the IPv6 packet as described in Section 4.1
of [RFC8754]. The text is reproduced below for reference.
| 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 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.
|
| When needed, the SRH is created as follows:
|
| The Next Header and Hdr Ext Len fields are set as specified in
| [RFC8200].
|
| The Routing Type field is set to 4.
|
| The DA of the packet is set with the value of the first segment.
|
| The first element of the SRH Segment List is the ultimate segment.
| The second element is the penultimate segment, and so on.
|
| The Segments Left field is set to n-1, where n is the number of
| elements in the SR Policy.
|
| The Last Entry field is set to n-1, where n is the number of
| elements in the SR Policy.
|
| TLVs (including HMAC) may be set according to their specification.
|
| The packet is forwarded toward the packet's Destination Address
| (the first segment).
|
| When a source does not require the entire SID list to be preserved
| in the SRH, a reduced SRH may be used.
|
| 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
| header), and the Last Entry field is set to n-2, where n is the
| number of elements in the SR Policy.
6.3. Rules for segment lists containing NEXT-C-SID flavor SIDs
1. If a Destination Option header would follow an SRH with a segment
list of more than one segment compressed as a single NEXT-C-SID
container, the SR source node MUST NOT omit the SRH.
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2. When the last Segment List entry (index 0) in the SRH is a C-SID
container representing more than one segment, the PSP operation
is performed at the segment preceding the first segment of this
C-SID container in the segment list. If the PSP behavior should
instead be performed at the penultimate segment along the path,
the SR source node MUST NOT compress the ultimate segment of the
segment list into a C-SID container.
3. If a Destination Option header would follow an SRH with a last
Segment List entry being a NEXT-C-SID container representing more
than one segment, the SR source node MUST ensure that the PSP
operation is not performed before the penultimate SR segment
endpoint node along the path.
6.4. Rules for segment lists containing REPLACE-C-SID flavor SIDs
1. All SIDs compressed in a REPLACE-C-SID sequence MUST share the
same Locator-Block and the same compression scheme.
2. All SIDs except the last one in a C-SID sequence for REPLACE-
C-SID MUST have the REPLACE-C-SID flavor. If the last C-SID
container is fully filled (i.e., the last C-SID is at position 0
in the C-SID container) and the last SID in the C-SID sequence is
not the last segment in the segment list, the last SID in the
C-SID sequence MUST NOT have the REPLACE-C-SID flavor.
3. When a REPLACE-C-SID flavor C-SID is present as the last SID in a
container that is not the last Segment List entry (index 0) in
the SRH, the next element in the segment list MUST be a REPLACE-
C-SID container in packed format carrying at least one C-SID.
The SR source node determines the compression scheme of REPLACE-C-SID
flavor SIDs as follows.
When receiving a SID advertisement for a REPLACE-C-SID flavor SID
with LNL=16, FL=0, AL=128-LBL-NL-FL, and the value of the Argument is
all 0, the SR source node marks both the SID and its locator as using
16-bit compression. All other SIDs allocated from this locator with
LNL=16, FL=16, AL=128-LBL-NL-FL, and the value of the Argument is all
0 are also marked as using 16-bit compression. When receiving a SID
advertisement for a REPLACE-C-SID flavor SID with LNFL=32, AL=128-
LBL-NL-FL, and the value of the Argument is all 0, the SR source node
marks both the SID and its locator as using 32-bit compression.
6.5. Upper-Layer Checksums
The Destination Address used in the IPv6 pseudo-header (Section 8.1
of [RFC8200]) is that of the ultimate destination.
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At the originating node, that address will be the Destination Address
as it is expected to be received by the ultimate destination. When
the last element in the compressed segment list is a C-SID container,
this address can be obtained from the last element in the
uncompressed segment list or by repeatedly applying the segment
behavior as described in Section 9.2. This applies regardless of
whether an SRH in present in the IPv6 packet or omitted.
At the recipient(s), that address will be in the Destination Address
field of the IPv6 header.
7. Inter-Domain Compression
Some SRv6 traffic may need to cross multiple routing domains, such as
different Autonomous Systems (ASes) or different routing areas within
an SR domain. Different routing domains may use different addressing
schema and Locator-Blocks.
A property of a C-SID sequence is that all C-SIDs in the sequence
share the same Locator-Block. Therefore, a segment list that spans
across multiple routing domains using different Locator-Blocks may
need a separate C-SID sequence for each domain.
This section defines an OPTIONAL solution to improve the efficiency
of C-SID compression in multi-domain environments by enabling a C-SID
sequence to combine C-SIDs having different Locator-Blocks.
The solution leverages two new SR segment endpoint behaviors,
"Endpoint with SRv6 Prefix Swap" ("End.PS" for short) and "Endpoint
with L3 cross-connect and SRv6 Prefix Swap" ("End.XPS" for short),
that enable modifying the Locator-Block for the next C-SID in the
C-SID sequence at the routing domain boundary.
7.1. End.PS: Prefix Swap
The End.PS behavior is a variant of the End behavior that modifies
the Locator-Block of the active C-SID sequence. This document
defines the End.PS behavior with the NEXT-C-SID flavor and the End.PS
behavior with the REPLACE-C-SID flavor.
An End.PS SID is used to transition to a new Locator-Block when the
routing domain boundary is on the SR segment endpoint node.
Each instance of an End.PS SID is associated with a target Locator-
Block B2/m, where B2 is an IPv6 address prefix and m is the
associated prefix length. The target Locator-Block is a local
property of the End.PS SID on the SR segment endpoint node.
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| 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 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 (Section 4.2 of [RFC8986]) and the
| lookup table of an End.DT6 SID (Section 4.6 of [RFC8986]).
The means by which an SR source node learns the target Locator-Block
associated with an End.PS SID are outside the scope of this document.
As examples, it could be learnt via configuration or signaled by a
controller.
7.1.1. End.PS with NEXT-C-SID
When processing an IPv6 packet that matches a FIB entry locally
instantiated as an End.PS SID with the NEXT-C-SID flavor and
associated with the target Locator-Block B2/m, the SR segment
endpoint node applies the procedure specified in Section 4.1.1 with
the lines N05 to N06 replaced as follows.
N05.1. Initialize an IPv6 address A equal to B2.
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.
7.1.2. End.PS with REPLACE-C-SID
When processing an IPv6 packet that matches a FIB entry locally
instantiated as an End.PS SID with the REPLACE-C-SID flavor and
associated with the target Locator-Block B2/m, the SR segment
endpoint node applies the procedure specified in Section 4.2.1 with
the line R20 replaced as follows.
R20.1. Initialize an IPv6 address A equal to B2.
R20.2. Write Segment List[Segments Left][DA.Arg.Index] into the bits
[m..m+LNFL-1] of the Destination Address of the IPv6 header.
R20.3. Copy A to the Destination Address of the IPv6 header.
7.2. End.XPS: L3 Cross-Connect and Prefix Swap
The End.XPS behavior is a variant of the End.X behavior that modifies
the Locator-Block of the active C-SID sequence. This document
defines the End.XPS behavior with the NEXT-C-SID flavor and the
End.XPS behavior with the REPLACE-C-SID flavor.
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An End.XPS SID is used to transition to a new Locator-Block when the
routing domain boundary is on a link adjacent to the SR segment
endpoint node.
Each instance of an End.XPS SID is associated with a target Locator-
Block B2/m and a set, J, of one or more L3 adjacencies. The target
Locator-Block and set of adjacencies are local properties of the
End.XPS SID on the SR segment endpoint node.
The means by which an SR source node learns the target Locator-Block
associated with an End.XPS SID are outside the scope of this
document. As examples, it could be learnt via configuration or
signaled by a controller.
7.2.1. End.XPS with NEXT-C-SID
When processing an IPv6 packet that matches a FIB entry locally
instantiated as an End.XPS SID with the NEXT-C-SID flavor and
associated with the target Locator-Block B2/m, the SR segment
endpoint node applies the procedure specified in Section 4.1.2 with
the lines N05 to N06 (of the pseudocode in Section 4.1.1) replaced as
follows.
N05.1. Initialize an IPv6 address A equal to B2.
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.
7.2.2. End.XPS with REPLACE-C-SID
When processing an IPv6 packet that matches a FIB entry locally
instantiated as an End.XPS SID with the REPLACE-C-SID flavor and
associated with the target Locator-Block B2/m, the SR segment
endpoint node applies the procedure specified in Section 4.2.2 with
the line R20 (of the pseudocode in Section 4.2.1) replaced as
follows.
R20.1. Initialize an IPv6 address A equal to B2.
R20.2. Write Segment List[Segments Left][DA.Arg.Index] into the bits
[m..m+LNFL-1] of the Destination Address of the IPv6 header.
R20.3. Copy A to the Destination Address of the IPv6 header.
8. Control Plane
This document does not require any new extensions to routing
protocols.
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Section 8 of [RFC8986] provides an overview of the control plane
protocols used for signaling of the SRv6 SIDs introduced by that
document. The SRv6 SIDs introduced by this document are advertised
using the same SRv6 extensions for various routing protocols, such as
* IS-IS [RFC9352]
* OSPFv3 [RFC9513]
* BGP [RFC9252], [RFC9514],
[I-D.ietf-idr-segment-routing-te-policy],
[I-D.ietf-idr-bgp-ls-sr-policy]
* PCEP [I-D.ietf-pce-segment-routing-ipv6]
The SR segment endpoint node MUST set the SID Argument bits to 0 when
advertising a locally instantiated SID of this document in the
routing protocol (e.g., IS-IS [RFC9352], OSPF [RFC9513], or BGP-LS
[RFC9514]).
Signaling the SRv6 SID Structure is REQUIRED for all the SIDs
introduced in this document. It is used by an SR source node to
compress a segment list as described in Section 6. 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. For example, for a SID of this document instantiated
from a /48 SRv6 SID block and a /64 Locator, and having a 16-bit
Function, the SRv6 SID Structure advertisement carries the following
values.
* Locator-Block length: 48
* Locator-Node length: 16
* Function length: 16
* Argument length: 48 (= 128-48-16-16)
A local C-SID MAY be advertised in the control plane individually
and/or in combination with a global C-SID instantiated on the same SR
segment endpoint node, with the End behavior, and the same Locator-
Block and flavor as the local C-SID. A combined global and local
C-SID is advertised as follows.
* The SID Locator-Block is that shared by the global and local
C-SIDs
* The SID Locator-Node is that of global C-SID
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* The SID Function is that of the local C-SID
* The SID Argument length is equal to 128-LBL-LNL-FL and the SID
Argument value is 0
* All other attributes of the SID (e.g., endpoint behavior or
algorithm) are those of the local C-SID
The local C-SID combined advertisement is needed in particular for
control plane protocols mandating that the SID is a subnet of a
locator advertised in the same protocol (e.g., Section 8 of [RFC9352]
and Section 9 of [RFC9513] for advertising Adjacency SIDs in IS-IS
and OSPFv3, respectively).
For a segment list computed by a controller and signaled to an SR
source node (e.g., via BGP [I-D.ietf-idr-segment-routing-te-policy]
or PCEP [I-D.ietf-pce-segment-routing-ipv6]), the controller provides
the ordered segment list comprising the uncompressed SIDs, with their
respective behavior and structure, to the SR source node. The SR
source node may then compress the segment list as described in
Section 6.
When a node that does not support this specification receives an
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]).
9. Operational Considerations
9.1. Pinging a SID
An SR source node may ping an SRv6 SID by sending an ICMPv6 echo
request packet destined to the SRv6 SID, with or without a segment
list. This operation is illustrated in Appendix A.1.2 of [RFC9259].
When pinging a SID of this document without a segment list, the SR
source node places the SID in the destination address of the ICMPv6
echo request and MUST set the Argument of the SID to 0. The Argument
value 0 allows the SID SR segment endpoint node (Section 4) to
identify itself as the ultimate destination of the packet and process
the ICMPv6 payload. If the SR source node sets a non-zero Argument
value, the SR segment endpoint node would instead attempt to
determine the next destination of the packet.
When pinging a SID of this document via a segment list, the SR source
node MUST construct the IPv6 packet as described in Section 6 and
compute the ICMPv6 checksum as described in Section 6.5.
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9.2. ICMP Error Processing
When an IPv6 node encounters an error while processing a packet, it
may 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 header may be required.
Section 5.4 of [RFC8754] defines the logic that an SR source node
follows to determine the ultimate destination of an invoking packet
containing an SRH.
For an SR source node that supports the compressed segment list
encoding defined in this document, the logic to determine the
ultimate destination is generalized as follows.
* If the destination address of the invoking IPv6 packet matches a
known SRv6 SID, modify the invoking IPv6 packet by applying the
SID behavior associated with the matched SRv6 SID;
* Repeat until the application of the SID behavior would result in
the processing of the upper-layer header.
The destination address of the resulting IPv6 packet may be used as
the ultimate destination of the invoking IPv6 packet.
Since the SR source node that needs to determine the ultimate
destination is the same node that originally built the segment list
in the invoking packet, it is able to perform this operation for all
the SIDs in the packet.
10. Implementation Status
This section is to be removed before publishing as an RFC.
RFC-Editor: Please clean up the references cited by this section
before publication.
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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 [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.
According to [RFC7942], "this will allow reviewers and working 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".
This section is provided in compliance with the SPRING working group
policies ([SPRING-WG-POLICIES]).
10.1. Cisco Systems
Cisco Systems reported the following implementations of the SR
segment endpoint node NEXT-C-SID flavor (Section 4.1) and the SR
source node efficient SID-list encoding (Section 6) for NEXT-C-SID
flavor SIDs. These are used as part of its SRv6 TI-LFA, micro-loop
avoidance, and traffic engineering functionalities.
* Cisco NCS 540 Series routers running IOS XR 7.3.x or above
[IMPL-CISCO-NCS540]
* Cisco NCS 560 Series routers running IOS XR 7.6.x or above
[IMPL-CISCO-NCS560]
* Cisco NCS 5500 Series routers running IOS XR 7.3.x or above
[IMPL-CISCO-NCS5500]
* Cisco NCS 5700 Series routers running IOS XR 7.5.x or above
[IMPL-CISCO-NCS5700]
* Cisco 8000 Series routers running IOS XR 7.5.x or above
[IMPL-CISCO-8000]
* Cisco ASR 9000 Series routers running IOS XR 7.5.x or above
[IMPL-CISCO-ASR9000]
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At the time of this report, all the implementations listed above are
in production and follow the specification in the latest version of
this document, including all the "MUST" and "SHOULD" clauses for the
NEXT-C-SID flavor.
This report was last updated on January 11, 2023.
10.2. Huawei Technologies
Huawei Technologies reported the following implementations of the SR
segment endpoint node REPLACE-C-SID flavor (Section 4.2). These are
used as part of its SRv6 TI-LFA, micro-loop avoidance, and traffic
engineering functionalities.
* Huawei ATN8XX,ATN910C,ATN980B routers running VRPV800R021C00 or
above.
* Huawei CX600-M2 routers running VRPV800R021C00 or above.
* Huawei NE40E,ME60-X1X2,ME60-X3X8X16 routers running VRPV800R021C00
or above.
* Huawei NE5000E,NE9000 routers running VRPV800R021C00 or above.
* Huawei NCE-IP Controller running V1R21C00 or above.
At the time of this report, all the implementations listed above are
in production and follow the specification in the latest version of
this document, including all the "MUST" and "SHOULD" clauses for the
REPLACE-C-SID flavor.
This report was last updated on January 11, 2023.
10.3. Nokia
Nokia reported the following implementations ([IMPL-NOKIA-20.10]) of
the SR segment endpoint node NEXT-C-SID flavor (Section 4.1). These
are used as part of its shortest path forwarding (in algorithm 0 and
Flex-Algo), remote and TI-LFA repair tunnel, and Traffic Engineering
functionalities.
* Nokia 7950 XRS 20/20e routers running SROS Release 22.10 or above
* Nokia 7750 SR-12e routers running SROS Release 22.10 or above
* Nokia 7750 SR-7/12 routers running SROS Release 22.10 or above
* Nokia 7750 SR-7s/14s routers running SROS Release 22.10 or above
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* Nokia 7750 SR-1/1s/2s routers running SROS Release 22.10 or above
At the time of this report, all the implementations listed above are
in production and follow the specification in the latest version of
this document, including all the "MUST" and "SHOULD" clauses for the
NEXT-C-SID flavor.
This report was last updated on February 3, 2023.
10.4. Arrcus
Arrcus reported the following implementations of the SR segment
endpoint node NEXT-C-SID flavor (Section 4.1). These are used as
part of its SRv6 shortest path forwarding (in algorithm 0 and Flex-
Algo), TI-LFA, micro-loop avoidance and Traffic Engineering
functionalities.
* Arrcus running on Ufi Space routers S9510-28DC, S9710-76D,
S9600-30DX and S9700-23D with ArcOS v5.2.1 or above
* Arrcus running n Ufi Space routers S9600-72XC and S9700-53DX with
ArcOS v5.1.1D or above
* Arrcus running on Quanta router IXA and IXAE with ArcOS v5.1.1D or
above
At the time of this report, all the implementations listed above are
in production and follow the specification in the latest version of
this document, including all the "MUST" and "SHOULD" clauses for the
NEXT-C-SID flavor.
This report was last updated on March 11, 2023.
10.5. Juniper Networks
Juniper Networks reported the following implementations of the SR
segment endpoint node NEXT-C-SID flavor (Section 4.1). These are
used as part of its SRv6 shortest path forwarding (in algorithm 0 and
Flex-Algo), TI-LFA, micro-loop avoidance, and Traffic Engineering
functionalities.
Juniper release 23.3 onwards supports this functionality.
At the time of this report, all the implementations listed above are
in development and follow the specification in the latest version of
this document, including all the "MUST" and "SHOULD" clauses for the
NEXT-C-SID flavor.
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This report was last updated on May 30, 2023.
10.6. Marvell
Marvell reported support in the Marvell Prestera Packet Processor for
the SR segment endpoint node NEXT-C-SID flavor (Section 4.1) and
REPLACE-C-SID flavor (Section 4.2).
This report was last updated on February 15, 2023.
10.7. Broadcom
Broadcom reported the following implementations of the SR segment
endpoint node NEXT-C-SID flavor (Section 4.1) and REPLACE-C-SID
flavor (Section 4.2). These are used as part of its SRv6 TI-LFA,
micro-loop avoidance, and traffic engineering functionalities. All
implementation of the following list is in general availability for
customers using BCM SDK 6.5.26 or above.
* 88850 (Jericho2c+) series
* 88690 (Jericho2) series
* 88800 (Jericho2c) series
* 88480 (Qunran2a) series
* 88280 (Qunran2u) series
* 88295 (Qunran2n) series
* 88830 (Jericho2x) series
At the time of this report, all the implementations listed above are
in production and follow the specification in the latest version of
this document, including all the "MUST" and "SHOULD" clauses for the
NEXT-C-SID and REPLACE-C-SID flavors.
For 78900 (Tomahawk) series-related support, please contact the
Broadcom team.
This report was last updated on February 21, 2023.
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10.8. ZTE Corporation
ZTE Corporation reported the following implementations of the SR
segment endpoint node REPLACE-C-SID flavor (Section 4.2). These are
used as part of its SRv6 TI-LFA, micro-loop avoidance, and traffic
engineering functionalities.
* ZTE M6000-18S(BRAS), M6000-8S Plus(BRAS) routers running
V5.00.10.09 or above.
* ZTE M6000-18S(SR), M6000-8S Plus(SR) routers running V5.00.10.80
or above.
* ZTE T8000-18 routers running V5.00.10.07 or above.
This report was last updated on March 29, 2023.
10.9. New H3C Technologies
New H3C Technologies reported the following implementations of the SR
segment endpoint node REPLACE-C-SID flavor (Section 4.2). These are
used as part of its SRv6 TI-LFA, micro-loop avoidance, and traffic
engineering functionalities.
* H3C CR16000-F, SR8800-X routers running Version 7.1.075 or above.
* H3C CR18000, CR19000 routers running Version 7.1.071 or above.
This report was last updated on March 29, 2023.
10.10. Ruijie Network
Ruijie Network reported the following implementations of the SR
segment endpoint node REPLACE-C-SID flavor (Section 4.2). These are
used as part of its SRv6 TI-LFA, micro-loop avoidance, and traffic
engineering functionalities.
* RUIJIE RG-N8018-R, RG-N8010-R routers running N8000-R_RGOS
12.8(3)B0801 or above.
This report was last updated on March 29, 2023.
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10.11. Ciena
Ciena reported the following implementations of the SR segment
endpoint node NEXT-C-SID flavor (Section 4.1). These are used as
part of its shortest path forwarding (in algorithm 0 and Flex-Algo),
remote and TI-LFA repair tunnel, and Traffic Engineering
functionalities.
The following platforms support implementation of the above.
* Ciena 5162, 5164, 5166, 5168 routers running SAOS 10.10 or above
* Ciena 8110, 8112, 8190 routers running SAOS 10.10 or above
At the time of this report, all the implementations listed above are
in production and follow the specification in the latest version of
this document, including all the "MUST" and "SHOULD" clauses for the
NEXT-C-SID flavor.
This report was last updated on February 6, 2024.
10.12. Centec
Centec reported the following implementations of the SR segment
endpoint node REPLACE-C-SID flavor (Section 4.2). These are used as
part of its SRv6 TI-LFA, micro-loop avoidance, and traffic
engineering functionalities. All implementation of the following
list is in general availability for customers using Centec SDK 5.6.8
or above.
* CTC7132 (TsingMa) Series
* CTC8180 (TsingMa.MX) Series
This report was last updated on February 14, 2024.
10.13. Open Source
The authors found the following open source implementations of the SR
segment endpoint node NEXT-C-SID flavor (Section 4.1).
* The Linux kernel, version 6.1 [IMPL-OSS-LINUX]
* The Software for Open Networking in the Cloud (SONiC), version
202212 [IMPL-OSS-SONIC], and Switch Abstraction Interface (SAI),
version 1.9.0 [IMPL-OSS-SAI]
* The Vector Packet Processor (VPP), version 20.05 [IMPL-OSS-VPP]
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* A generic P4 implementation [IMPL-OSS-P4]
The authors found the following open source implementations of the SR
segment endpoint node REPLACE-C-SID flavor (Section 4.2).
* ONOS and P4 Programmable Switch based [IMPL-OSS-ONOS]
* Open SRv6 Project [IMPL-OSS-OPEN-SRV6]
This section was last updated on January 11, 2023.
10.14. Interoperability Reports
10.14.1. Bell Canada / Ciena 2023
Bell Canada is currently evaluating interoperability between Ciena
and Cisco implementations of the NEXT-C-SID flavor defined in this
document. Further information will be added to this section when the
evaluation is complete.
10.14.2. EANTC 2023
In April 2023, the European Advanced Networking Test Center (EANTC)
successfully validated multiple implementations of SRv6 NEXT-C-SID
flavor (a.k.a., SRv6 uSID) [EANTC-23].
The participating vendors included Arista, Arrcus, Cisco, Huawei,
Juniper, Keysight, Nokia, and Spirent.
10.14.3. China Mobile 2020
In November 2020, China Mobile successfully validated multiple
interoperable implementations of the NEXT-C-SID and REPLACE-C-SID
flavors defined in this document.
This testing covered two different implementations of the SRv6
endpoint flavors defined in this document:
* Hardware implementation in Cisco ASR 9000 running IOS XR
* Software implementation in Cisco IOS XRv9000 virtual appliance
* Hardware implementation in Huawei NE40E and NE5000E running VRP
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 <S1, S2, S3, S4, S5, S6, S7>, where S1..S7 are SIDs instantiated
on SR segment endpoint nodes N1..N7, respectively.
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N0 --- N1 --- N2 --- N3 --- N4 --- N5 --- N6 --- N7
(S1) (S2) (S3) (S4) (S5) (S6) (S7)
* N0 is a generic packet generator.
* N1, N2, and N3 are Huawei routers.
* N4, N5, and N6 are Cisco routers.
* N7 is a generic traffic generator acting as a packet receiver.
The SR source node N0 steers the packets onto the SR policy by
setting the IPv6 destination address and creating an SRH (as
described in Section 4.1 of [RFC8754]) using a compressed segment
list encoding. The length of the compressed segment list encoding
varies for each scenario.
All SR segment endpoint nodes execute a variant of the End behavior:
regular End behavior (as defined in Section 4.1 of [RFC8986]), End
behavior with NEXT-C-SID flavor, and End behavior with REPLACE-C-SID
flavor. The variant being used at each SR segment endpoint node
varies for each scenario.
The interoperability was validated for the following scenarios:
*Scenario 1:*
* S1 and S2 are associated with the End behavior with the REPLACE-
C-SID flavor
* S3 is associated with the regular End behavior (no flavor)
* S4, S5, and S6 are associated with the End behavior with the NEXT-
C-SID flavor
* The SR source node imposes a compressed segment list encoding of 3
SIDs.
*Scenario 2:*
* S1, S2..., S6 are associated with the End behavior with the NEXT-
C-SID flavor
* The SR source node imposes a compressed segment list encoding of 2
SIDs.
*Scenario 3:*
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* S1, S2..., S6 are associated with the End behavior with the
REPLACE-C-SID flavor
* The SR source node imposes a compressed segment list encoding of 3
SIDs.
11. Applicability to other SR Segment Endpoint Behaviors
Future documents may extend the applicability of the NEXT-C-SID and
REPLACE-C-SID flavors to other SR segment endpoint behaviors.
For an SR segment endpoint behavior that can be used before the last
position of a segment list, a C-SID flavor is defined by reproducing
the same logic as described in Section 4.1 and Section 4.2 of this
document to determine the next segment in the segment list.
12. Security Considerations
Section 8 of [RFC8402] discusses the security considerations for
Segment Routing.
Section 5 of [RFC8754] describes the intra-SR-domain deployment model
and how to secure it. Section 7 of [RFC8754] describes the threats
applicable to SRv6 and how to mitigate them.
Section 9 of [RFC8986] discusses the security considerations
applicable to the SRv6 network programming framework, as well as the
SR source node and SR segment endpoint node behaviors that it
defines.
This document introduces two new flavors for some of the SR segment
endpoint 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.
An SR source node constructs an IPv6 packet with a compressed segment
list as defined in Sections 3.1 and 4.1 of [RFC8754] and Section 5 of
[RFC8986]. The paths that an SR source node may enforce using a
compressed segment list are the same, from a topology and service
perspective, as those that an SR source node could enforce using the
SIDs of [RFC8986].
An SR segment endpoint node processes an IPv6 packet matching a
locally instantiated SID as defined in [RFC8986], with the pseudocode
modifications in Section 4 of this document. These modifications
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 adjacency segment instantiated with the End.X
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behavior remains an adjacency segment regardless of whether it uses
the unflavored End.X behavior defined in Section 4.2 of [RFC8986] or
a C-SID flavor of that behavior. This document does not introduce
any new SID semantic.
Any other transit node processes the packet as described in
Section 4.2 of [RFC8754].
This document defines a new method of encoding the SIDs inside a
segment list at the SR source node and decoding them at the SR
segment endpoint node, but it does not change how the segment list
itself is encoded in the IPv6 packet nor the semantic of any segment
that it comprises. Therefore, this document is subject to the same
security considerations that are discussed in [RFC8402], [RFC8754],
and [RFC8986].
13. IANA Considerations
13.1. SRv6 Endpoint Behaviors
This I-D. requests the IANA to update the reference of the following
registrations from the "SRv6 Endpoint Behaviors" registry under the
top-level "Segment Routing" registry-group
(https://www.iana.org/assignments/segment-routing/) with the RFC
number of this document once it is published, and transfer change
control to the IETF.
+=======+=========================================+===========+
| Value | Description | Reference |
+=======+=========================================+===========+
| 43 | End with NEXT-CSID | This I-D. |
+-------+-----------------------------------------+-----------+
| 44 | End with NEXT-CSID & PSP | This I-D. |
+-------+-----------------------------------------+-----------+
| 45 | End with NEXT-CSID & USP | This I-D. |
+-------+-----------------------------------------+-----------+
| 46 | End with NEXT-CSID, PSP & USP | This I-D. |
+-------+-----------------------------------------+-----------+
| 47 | End with NEXT-CSID & USD | This I-D. |
+-------+-----------------------------------------+-----------+
| 48 | End with NEXT-CSID, PSP & USD | This I-D. |
+-------+-----------------------------------------+-----------+
| 49 | End with NEXT-CSID, USP & USD | This I-D. |
+-------+-----------------------------------------+-----------+
| 50 | End with NEXT-CSID, PSP, USP & USD | This I-D. |
+-------+-----------------------------------------+-----------+
| 52 | End.X with NEXT-CSID | This I-D. |
+-------+-----------------------------------------+-----------+
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| 53 | End.X with NEXT-CSID & PSP | This I-D. |
+-------+-----------------------------------------+-----------+
| 54 | End.X with NEXT-CSID & USP | This I-D. |
+-------+-----------------------------------------+-----------+
| 55 | End.X with NEXT-CSID, PSP & USP | This I-D. |
+-------+-----------------------------------------+-----------+
| 56 | End.X with NEXT-CSID & USD | This I-D. |
+-------+-----------------------------------------+-----------+
| 57 | End.X with NEXT-CSID, PSP & USD | This I-D. |
+-------+-----------------------------------------+-----------+
| 58 | End.X with NEXT-CSID, USP & USD | This I-D. |
+-------+-----------------------------------------+-----------+
| 59 | End.X with NEXT-CSID, PSP, USP & USD | This I-D. |
+-------+-----------------------------------------+-----------+
| 85 | End.T with NEXT-CSID | This I-D. |
+-------+-----------------------------------------+-----------+
| 86 | End.T with NEXT-CSID & PSP | This I-D. |
+-------+-----------------------------------------+-----------+
| 87 | End.T with NEXT-CSID & USP | This I-D. |
+-------+-----------------------------------------+-----------+
| 88 | End.T with NEXT-CSID, PSP & USP | This I-D. |
+-------+-----------------------------------------+-----------+
| 89 | End.T with NEXT-CSID & USD | This I-D. |
+-------+-----------------------------------------+-----------+
| 90 | End.T with NEXT-CSID, PSP & USD | This I-D. |
+-------+-----------------------------------------+-----------+
| 91 | End.T with NEXT-CSID, USP & USD | This I-D. |
+-------+-----------------------------------------+-----------+
| 92 | End.T with NEXT-CSID, PSP, USP & USD | This I-D. |
+-------+-----------------------------------------+-----------+
| 93 | End.B6.Encaps with NEXT-CSID | This I-D. |
+-------+-----------------------------------------+-----------+
| 94 | End.B6.Encaps.Red with NEXT-CSID | This I-D. |
+-------+-----------------------------------------+-----------+
| 95 | End.BM with NEXT-CSID | This I-D. |
+-------+-----------------------------------------+-----------+
| 96 | End.PS with NEXT-CSID | This I-D. |
+-------+-----------------------------------------+-----------+
| 97 | End.XPS with NEXT-CSID | This I-D. |
+-------+-----------------------------------------+-----------+
| 101 | End with REPLACE-CSID | This I-D. |
+-------+-----------------------------------------+-----------+
| 102 | End with REPLACE-CSID & PSP | This I-D. |
+-------+-----------------------------------------+-----------+
| 103 | End with REPLACE-CSID & USP | This I-D. |
+-------+-----------------------------------------+-----------+
| 104 | End with REPLACE-CSID, PSP & USP | This I-D. |
+-------+-----------------------------------------+-----------+
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| 105 | End.X with REPLACE-CSID | This I-D. |
+-------+-----------------------------------------+-----------+
| 106 | End.X with REPLACE-CSID & PSP | This I-D. |
+-------+-----------------------------------------+-----------+
| 107 | End.X with REPLACE-CSID & USP | This I-D. |
+-------+-----------------------------------------+-----------+
| 108 | End.X with REPLACE-CSID, PSP & USP | This I-D. |
+-------+-----------------------------------------+-----------+
| 109 | End.T with REPLACE-CSID | This I-D. |
+-------+-----------------------------------------+-----------+
| 110 | End.T with REPLACE-CSID & PSP | This I-D. |
+-------+-----------------------------------------+-----------+
| 111 | End.T with REPLACE-CSID & USP | This I-D. |
+-------+-----------------------------------------+-----------+
| 112 | End.T with REPLACE-CSID, PSP & USP | This I-D. |
+-------+-----------------------------------------+-----------+
| 114 | End.B6.Encaps with REPLACE-CSID | This I-D. |
+-------+-----------------------------------------+-----------+
| 115 | End.BM with REPLACE-CSID | This I-D. |
+-------+-----------------------------------------+-----------+
| 116 | End.DX6 with REPLACE-CSID | This I-D. |
+-------+-----------------------------------------+-----------+
| 117 | End.DX4 with REPLACE-CSID | This I-D. |
+-------+-----------------------------------------+-----------+
| 118 | End.DT6 with REPLACE-CSID | This I-D. |
+-------+-----------------------------------------+-----------+
| 119 | End.DT4 with REPLACE-CSID | This I-D. |
+-------+-----------------------------------------+-----------+
| 120 | End.DT46 with REPLACE-CSID | This I-D. |
+-------+-----------------------------------------+-----------+
| 121 | End.DX2 with REPLACE-CSID | This I-D. |
+-------+-----------------------------------------+-----------+
| 122 | End.DX2V with REPLACE-CSID | This I-D. |
+-------+-----------------------------------------+-----------+
| 123 | End.DT2U with REPLACE-CSID | This I-D. |
+-------+-----------------------------------------+-----------+
| 124 | End.DT2M with REPLACE-CSID | This I-D. |
+-------+-----------------------------------------+-----------+
| 127 | End.B6.Encaps.Red with REPLACE-CSID | This I-D. |
+-------+-----------------------------------------+-----------+
| 128 | End with REPLACE-CSID & USD | This I-D. |
+-------+-----------------------------------------+-----------+
| 129 | End with REPLACE-CSID, PSP & USD | This I-D. |
+-------+-----------------------------------------+-----------+
| 130 | End with REPLACE-CSID, USP & USD | This I-D. |
+-------+-----------------------------------------+-----------+
| 131 | End with REPLACE-CSID, PSP, USP & USD | This I-D. |
+-------+-----------------------------------------+-----------+
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| 132 | End.X with REPLACE-CSID & USD | This I-D. |
+-------+-----------------------------------------+-----------+
| 133 | End.X with REPLACE-CSID, PSP & USD | This I-D. |
+-------+-----------------------------------------+-----------+
| 134 | End.X with REPLACE-CSID, USP & USD | This I-D. |
+-------+-----------------------------------------+-----------+
| 135 | End.X with REPLACE-CSID, PSP, USP & USD | This I-D. |
+-------+-----------------------------------------+-----------+
| 136 | End.T with REPLACE-CSID & USD | This I-D. |
+-------+-----------------------------------------+-----------+
| 137 | End.T with REPLACE-CSID, PSP & USD | This I-D. |
+-------+-----------------------------------------+-----------+
| 138 | End.T with REPLACE-CSID, USP & USD | This I-D. |
+-------+-----------------------------------------+-----------+
| 139 | End.T with REPLACE-CSID, PSP, USP & USD | This I-D. |
+-------+-----------------------------------------+-----------+
| 140 | End.PS with REPLACE-CSID | This I-D. |
+-------+-----------------------------------------+-----------+
| 141 | End.XPS with REPLACE-CSID | This I-D. |
+-------+-----------------------------------------+-----------+
Table 1: Registration List
14. Acknowledgements
The authors would like to thank Kamran Raza, Xing Jiang, YuanChao Su,
Han Li, Yisong Liu, Martin Vigoureux, Joel Halpern, and Tal Mizrahi
for their insightful feedback and suggestions.
The authors would also like to thank Andrew Alston, Linda Dunbar,
Adrian Farrel, and Boris Hassanov for their thorough review of this
document.
15. References
15.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
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[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
[RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
<https://www.rfc-editor.org/info/rfc8754>.
[RFC8986] Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
(SRv6) Network Programming", RFC 8986,
DOI 10.17487/RFC8986, February 2021,
<https://www.rfc-editor.org/info/rfc8986>.
[RFC9259] Ali, Z., Filsfils, C., Matsushima, S., Voyer, D., and M.
Chen, "Operations, Administration, and Maintenance (OAM)
in Segment Routing over IPv6 (SRv6)", RFC 9259,
DOI 10.17487/RFC9259, June 2022,
<https://www.rfc-editor.org/info/rfc9259>.
[RFC9350] Psenak, P., Ed., Hegde, S., Filsfils, C., Talaulikar, K.,
and A. Gulko, "IGP Flexible Algorithm", RFC 9350,
DOI 10.17487/RFC9350, February 2023,
<https://www.rfc-editor.org/info/rfc9350>.
15.2. Informative References
[EANTC-23] European Advanced Networking Test Center (EANTC), "Multi-
Vendor MPLS SDN Interoperability Test Report", 18 April
2023,
<https://eantc.de/fileadmin/eantc/downloads/events/2023/
EANTC-InteropTest2023-TestReport.pdf>.
[GKP94] Graham, R., Knuth, D., and O. Patashnik, "Concrete
Mathematics: A Foundation for Computer Science",
ISBN 9780201558029, 1994.
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[I-D.ietf-6man-sids]
Krishnan, S., "SRv6 Segment Identifiers in the IPv6
Addressing Architecture", Work in Progress, Internet-
Draft, draft-ietf-6man-sids-06, 15 February 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-6man-
sids-06>.
[I-D.ietf-idr-bgp-ls-sr-policy]
Previdi, S., Talaulikar, K., Dong, J., Gredler, H., and J.
Tantsura, "Advertisement of Segment Routing Policies using
BGP Link-State", Work in Progress, Internet-Draft, draft-
ietf-idr-bgp-ls-sr-policy-03, 5 November 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-bgp-
ls-sr-policy-03>.
[I-D.ietf-idr-segment-routing-te-policy]
Previdi, S., Filsfils, C., Talaulikar, K., Mattes, P., and
D. Jain, "Advertising Segment Routing Policies in BGP",
Work in Progress, Internet-Draft, draft-ietf-idr-segment-
routing-te-policy-26, 23 October 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-
segment-routing-te-policy-26>.
[I-D.ietf-pce-segment-routing-ipv6]
Li, C., Kaladharan, P., Sivabalan, S., Koldychev, M., and
Y. Zhu, "Path Computation Element Communication Protocol
(PCEP) Extensions for Segment Routing leveraging the IPv6
dataplane", Work in Progress, Internet-Draft, draft-ietf-
pce-segment-routing-ipv6-22, 15 February 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-pce-
segment-routing-ipv6-22>.
[IMPL-CISCO-8000]
Cisco Systems, "Segment Routing Configuration Guide for
Cisco 8000 Series Routers", 4 November 2022,
<https://www.cisco.com/c/en/us/td/docs/iosxr/cisco8000/
segment-routing/75x/b-segment-routing-cg-cisco8000-75x/
configuring-segment-routing-over-ipv6-srv6-micro-
sids.html>.
[IMPL-CISCO-ASR9000]
Cisco Systems, "Segment Routing Configuration Guide for
Cisco ASR 9000 Series Routers", 6 November 2022,
<https://www.cisco.com/c/en/us/td/docs/routers/asr9000/
software/asr9k-r7-5/segment-routing/configuration/guide/b-
segment-routing-cg-asr9000-75x/configure-srv6-micro-
sid.html>.
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[IMPL-CISCO-NCS540]
Cisco Systems, "Segment Routing Configuration Guide for
Cisco NCS 540 Series Routers", 2 November 2022,
<https://www.cisco.com/c/en/us/td/docs/iosxr/ncs5xx/
segment-routing/73x/b-segment-routing-cg-73x-ncs540/
configure-srv6.html>.
[IMPL-CISCO-NCS5500]
Cisco Systems, "Segment Routing Configuration Guide for
Cisco NCS 5500 Series Routers", 6 November 2022,
<https://www.cisco.com/c/en/us/td/docs/iosxr/ncs5500/
segment-routing/73x/b-segment-routing-cg-ncs5500-73x/
configure-srv6-micro-sid.html>.
[IMPL-CISCO-NCS560]
Cisco Systems, "Segment Routing Configuration Guide for
Cisco NCS 560 Series Routers", 14 October 2022,
<https://www.cisco.com/c/en/us/td/docs/iosxr/ncs560/
segment-routing/76x/b-segment-routing-cg-76x-ncs560/m-
configure-srv6-usid-ncs5xx.html>.
[IMPL-CISCO-NCS5700]
Cisco Systems, "Segment Routing Configuration Guide for
Cisco NCS 5700 Series Routers", 6 November 2022,
<https://www.cisco.com/c/en/us/td/docs/iosxr/ncs5500/
segment-routing/75x/b-segment-routing-cg-ncs5500-75x/
configure-srv6-micro-sid.html>.
[IMPL-NOKIA-20.10]
Nokia, "Segment Routing and PCE User Guide", December
2022, <https://documentation.nokia.com/sr/22-
10/books/Segment%20Routing%20and%20PCE%20User%20Guide/
segment-rout-with-ipv6-data-plane-srv6.html>.
[IMPL-OSS-LINUX]
Abeni, P., "Add NEXT-C-SID support for SRv6 End behavior",
20 September 2022,
<https://git.kernel.org/pub/scm/linux/kernel/git/netdev/
net-next.git/
commit/?id=cec9d59e89362809f17f2d854faf52966216da13>.
[IMPL-OSS-ONOS]
Open Networking Foundation, "Stratum CMCC G-SRv6 Project",
24 March 2021,
<https://wiki.opennetworking.org/display/COM/
Stratum+CMCC+G-SRv6+Project>.
Cheng, et al. Expires 1 September 2024 [Page 51]
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[IMPL-OSS-OPEN-SRV6]
"Open SRv6 Project", n.d.,
<http://opensrv6.org.cn/en/srv6-2/>.
[IMPL-OSS-P4]
Salsano, S. and A. Tulumello, "SRv6 uSID (micro SID)
implementation on P4", 3 January 2021,
<https://github.com/netgroup/p4-srv6-usid>.
[IMPL-OSS-SAI]
Agrawal, A., "Added new behaviors to support uSID
instruction", 8 June 2021,
<https://github.com/opencomputeproject/SAI/pull/1231/
commits/02e58d95ad966ca9efc24eb9e0c0fa10b21de2a4>.
[IMPL-OSS-SONIC]
Shah, S. and R. Sudarshan, "SONiC uSID", 21 August 2022,
<https://github.com/sonic-net/SONiC/blob/master/doc/srv6/
SRv6_uSID.md>.
[IMPL-OSS-VPP]
FD.io, "Srv6 cli reference", n.d., <https://s3-
docs.fd.io/vpp/23.02/cli-reference/clis/
clicmd_src_vnet_srv6.html>.
[RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", BCP 205,
RFC 7942, DOI 10.17487/RFC7942, July 2016,
<https://www.rfc-editor.org/info/rfc7942>.
[RFC9252] Dawra, G., Ed., Talaulikar, K., Ed., Raszuk, R., Decraene,
B., Zhuang, S., and J. Rabadan, "BGP Overlay Services
Based on Segment Routing over IPv6 (SRv6)", RFC 9252,
DOI 10.17487/RFC9252, July 2022,
<https://www.rfc-editor.org/info/rfc9252>.
[RFC9352] Psenak, P., Ed., Filsfils, C., Bashandy, A., Decraene, B.,
and Z. Hu, "IS-IS Extensions to Support Segment Routing
over the IPv6 Data Plane", RFC 9352, DOI 10.17487/RFC9352,
February 2023, <https://www.rfc-editor.org/info/rfc9352>.
[RFC9513] Li, Z., Hu, Z., Talaulikar, K., Ed., and P. Psenak,
"OSPFv3 Extensions for Segment Routing over IPv6 (SRv6)",
RFC 9513, DOI 10.17487/RFC9513, December 2023,
<https://www.rfc-editor.org/info/rfc9513>.
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[RFC9514] Dawra, G., Filsfils, C., Talaulikar, K., Ed., Chen, M.,
Bernier, D., and B. Decraene, "Border Gateway Protocol -
Link State (BGP-LS) Extensions for Segment Routing over
IPv6 (SRv6)", RFC 9514, DOI 10.17487/RFC9514, December
2023, <https://www.rfc-editor.org/info/rfc9514>.
[SPRING-WG-POLICIES]
SPRING Working Group Chairs, "SPRING Working Group
Policies", 14 October 2022,
<https://wiki.ietf.org/en/group/spring/WG_Policies>.
Appendix A. Complete pseudocodes
The content of this section is purely informative rendering of the
pseudocodes of [RFC8986] with the modifications in this document.
This rendering may not be used as a reference.
A.1. End with NEXT-C-SID
When processing the SRH of a packet matching a FIB entry locally
instantiated as an End SID with the NEXT-C-SID flavor:
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N01. If (DA.Argument != 0) {
N02. If (IPv6 Hop Limit <= 1) {
N03. Send an ICMP Time Exceeded message to the Source Address
with Code 0 (Hop limit exceeded in transit),
interrupt packet processing, and discard the packet.
N04. }
N05. Copy DA.Argument into the bits [LBL..(LBL+AL-1)] of the
Destination Address.
N06. Set the bits [(LBL+AL)..127] of the Destination Address to
zero.
N07. Decrement IPv6 Hop Limit by 1.
N08. Submit the packet to the egress IPv6 FIB lookup for
transmission to the next destination.
N09. }
S02. If (Segments Left == 0) {
S03. Stop processing the SRH, and proceed to process the next
header in the packet, whose type is identified by
the Next Header field in the routing header.
S04. }
S05. If (IPv6 Hop Limit <= 1) {
S06. Send an ICMP Time Exceeded message to the Source Address
with Code 0 (Hop limit exceeded in transit),
interrupt packet processing, and discard the packet.
S07. }
S08. max_LE = (Hdr Ext Len / 2) - 1
S09. If ((Last Entry > max_LE) or (Segments Left > Last Entry+1)) {
S10. Send an ICMP Parameter Problem to the Source Address
with Code 0 (Erroneous header field encountered)
and Pointer set to the Segments Left field,
interrupt packet processing, and discard the packet.
S11. }
S12. Decrement IPv6 Hop Limit by 1.
S13. Decrement Segments Left by 1.
S14. Update IPv6 DA with Segment List[Segments Left].
S15. Submit the packet to the egress IPv6 FIB lookup for
transmission to the new destination.
Before processing the Upper-Layer header or any IPv6 extension header
other than Hop-by-Hop or Destination Option of a packet matching a
FIB entry locally instantiated as an End SID with the NEXT-C-SID
flavor:
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N01. If (DA.Argument != 0) {
N02. If (IPv6 Hop Limit <= 1) {
N03. Send an ICMP Time Exceeded message to the Source Address,
Code 0 (Hop limit exceeded in transit),
interrupt packet processing and discard the packet.
N04. }
N05. Copy DA.Argument into the bits [LBL..(LBL+AL-1)] of the
Destination Address.
N06. Set the bits [(LBL+AL)..127] of the Destination Address to
zero.
N07. Decrement IPv6 Hop Limit by 1.
N08. Submit the packet to the egress IPv6 FIB lookup for
transmission to the next destination.
N09. }
When processing the Upper-Layer header of a packet matching a FIB
entry locally instantiated as an End SID with the NEXT-C-SID flavor:
S01. If (Upper-Layer header type is allowed by local configuration) {
S02. Proceed to process the Upper-Layer header
S03. } Else {
S04. Send an ICMP Parameter Problem to the Source Address
with Code 4 (SR Upper-layer Header Error)
and Pointer set to the offset of the Upper-Layer header,
interrupt packet processing, and discard the packet.
S05. }
A.2. End.X with NEXT-C-SID
When processing the SRH of a packet matching a FIB entry locally
instantiated as an End.X SID with the NEXT-C-SID flavor:
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N01. If (DA.Argument != 0) {
N02. If (IPv6 Hop Limit <= 1) {
N03. Send an ICMP Time Exceeded message to the Source Address
with Code 0 (Hop limit exceeded in transit),
interrupt packet processing, and discard the packet.
N04. }
N05. Copy DA.Argument into the bits [LBL..(LBL+AL-1)] of the
Destination Address.
N06. Set the bits [(LBL+AL)..127] of the Destination Address to
zero.
N07. Decrement IPv6 Hop Limit by 1.
N08. Submit the packet to the IPv6 module for transmission to the
new destination via a member of J.
N09. }
S02. If (Segments Left == 0) {
S03. Stop processing the SRH, and proceed to process the next
header in the packet, whose type is identified by
the Next Header field in the routing header.
S04. }
S05. If (IPv6 Hop Limit <= 1) {
S06. Send an ICMP Time Exceeded message to the Source Address
with Code 0 (Hop limit exceeded in transit),
interrupt packet processing, and discard the packet.
S07. }
S08. max_LE = (Hdr Ext Len / 2) - 1
S09. If ((Last Entry > max_LE) or (Segments Left > Last Entry+1)) {
S10. Send an ICMP Parameter Problem to the Source Address
with Code 0 (Erroneous header field encountered)
and Pointer set to the Segments Left field,
interrupt packet processing, and discard the packet.
S11. }
S12. Decrement IPv6 Hop Limit by 1.
S13. Decrement Segments Left by 1.
S14. Update IPv6 DA with Segment List[Segments Left].
S15. Submit the packet to the IPv6 module for transmission
to the new destination via a member of J.
Before processing the Upper-Layer header or any IPv6 extension header
other than Hop-by-Hop or Destination Option of a packet matching a
FIB entry locally instantiated as an End.X SID with the NEXT-C-SID
flavor:
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N01. If (DA.Argument != 0) {
N02. If (IPv6 Hop Limit <= 1) {
N03. Send an ICMP Time Exceeded message to the Source Address,
Code 0 (Hop limit exceeded in transit),
interrupt packet processing and discard the packet.
N04. }
N05. Copy DA.Argument into the bits [LBL..(LBL+AL-1)] of the
Destination Address.
N06. Set the bits [(LBL+AL)..127] of the Destination Address to
zero.
N07. Decrement IPv6 Hop Limit by 1.
N08. Submit the packet to the IPv6 module for transmission to the
new destination via a member of J.
N09. }
When processing the Upper-Layer header of a packet matching a FIB
entry locally instantiated as an End.X SID with the NEXT-C-SID
flavor:
S01. If (Upper-Layer header type is allowed by local configuration) {
S02. Proceed to process the Upper-Layer header
S03. } Else {
S04. Send an ICMP Parameter Problem to the Source Address
with Code 4 (SR Upper-layer Header Error)
and Pointer set to the offset of the Upper-Layer header,
interrupt packet processing, and discard the packet.
S05. }
A.3. End.T with NEXT-C-SID
When processing the SRH of a packet matching a FIB entry locally
instantiated as an End.T SID with the NEXT-C-SID flavor:
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N01. If (DA.Argument != 0) {
N02. If (IPv6 Hop Limit <= 1) {
N03. Send an ICMP Time Exceeded message to the Source Address
with Code 0 (Hop limit exceeded in transit),
interrupt packet processing, and discard the packet.
N04. }
N05. Copy DA.Argument into the bits [LBL..(LBL+AL-1)] of the
Destination Address.
N06. Set the bits [(LBL+AL)..127] of the Destination Address to
zero.
N07. Decrement IPv6 Hop Limit by 1.
N08.1. Set the packet's associated FIB table to T.
N08.2. Submit the packet to the egress IPv6 FIB lookup for
transmission to the new destination.
N09. }
S02. If (Segments Left == 0) {
S03. Stop processing the SRH, and proceed to process the next
header in the packet, whose type is identified by
the Next Header field in the routing header.
S04. }
S05. If (IPv6 Hop Limit <= 1) {
S06. Send an ICMP Time Exceeded message to the Source Address
with Code 0 (Hop limit exceeded in transit),
interrupt packet processing, and discard the packet.
S07. }
S08. max_LE = (Hdr Ext Len / 2) - 1
S09. If ((Last Entry > max_LE) or (Segments Left > Last Entry+1)) {
S10. Send an ICMP Parameter Problem to the Source Address
with Code 0 (Erroneous header field encountered)
and Pointer set to the Segments Left field,
interrupt packet processing, and discard the packet.
S11. }
S12. Decrement IPv6 Hop Limit by 1.
S13. Decrement Segments Left by 1.
S14. Update IPv6 DA with Segment List[Segments Left].
S15.1. Set the packet's associated FIB table to T.
S15.2. Submit the packet to the egress IPv6 FIB lookup for
transmission to the new destination.
Before processing the Upper-Layer header or any IPv6 extension header
other than Hop-by-Hop or Destination Option of a packet matching a
FIB entry locally instantiated as an End.T SID with the NEXT-C-SID
flavor:
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N01. If (DA.Argument != 0) {
N02. If (IPv6 Hop Limit <= 1) {
N03. Send an ICMP Time Exceeded message to the Source Address,
Code 0 (Hop limit exceeded in transit),
interrupt packet processing and discard the packet.
N04. }
N05. Copy DA.Argument into the bits [LBL..(LBL+AL-1)] of the
Destination Address.
N06. Set the bits [(LBL+AL)..127] of the Destination Address to
zero.
N07. Decrement IPv6 Hop Limit by 1.
N08.1. Set the packet's associated FIB table to T.
N08.2. Submit the packet to the egress IPv6 FIB lookup for
transmission to the new destination.
N09. }
When processing the Upper-Layer header of a packet matching a FIB
entry locally instantiated as an End.T SID with the NEXT-C-SID
flavor:
S01. If (Upper-Layer header type is allowed by local configuration) {
S02. Proceed to process the Upper-Layer header
S03. } Else {
S04. Send an ICMP Parameter Problem to the Source Address
with Code 4 (SR Upper-layer Header Error)
and Pointer set to the offset of the Upper-Layer header,
interrupt packet processing, and discard the packet.
S05. }
A.4. End.B6.Encaps with NEXT-C-SID
When processing the SRH of a packet matching a FIB entry locally
instantiated as an End.B6.Encaps SID with the NEXT-C-SID flavor:
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N01. If (DA.Argument != 0) {
N02. If (IPv6 Hop Limit <= 1) {
N03. Send an ICMP Time Exceeded message to the Source Address,
Code 0 (Hop limit exceeded in transit),
interrupt packet processing and discard the packet.
N04. }
N05. Copy DA.Argument into the bits [LBL..(LBL+AL-1)] of the
Destination Address.
N06. Set the bits [(LBL+AL)..127] of the Destination Address to
zero.
N07. Decrement IPv6 Hop Limit by 1.
N08.1. Push a new IPv6 header with its own SRH containing B.
N08.2. Set the outer IPv6 SA to A.
N08.3. Set the outer IPv6 DA to the first SID of B.
N08.4. Set the outer Payload Length, Traffic Class, Flow Label,
Hop Limit, and Next Header fields.
N08.5. Submit the packet to the egress IPv6 FIB lookup for
transmission to the next destination.
N09. }
S02. If (Segments Left == 0) {
S03. Stop processing the SRH, and proceed to process the next
header in the packet, whose type is identified by
the Next Header field in the routing header.
S04. }
S05. If (IPv6 Hop Limit <= 1) {
S06. Send an ICMP Time Exceeded message to the Source Address
with Code 0 (Hop limit exceeded in transit),
interrupt packet processing, and discard the packet.
S07. }
S08. max_LE = (Hdr Ext Len / 2) - 1
S09. If ((Last Entry > max_LE) or (Segments Left > Last Entry+1)) {
S10. Send an ICMP Parameter Problem to the Source Address
with Code 0 (Erroneous header field encountered)
and Pointer set to the Segments Left field,
interrupt packet processing, and discard the packet.
S11. }
S12. Decrement IPv6 Hop Limit by 1.
S13. Decrement Segments Left by 1.
S14. Update IPv6 DA with Segment List[Segments Left].
S15. Push a new IPv6 header with its own SRH containing B.
S16. Set the outer IPv6 SA to A.
S17. Set the outer IPv6 DA to the first SID of B.
S18. Set the outer Payload Length, Traffic Class, Flow Label,
Hop Limit, and Next Header fields.
S19. Submit the packet to the egress IPv6 FIB lookup for
transmission to the new destination.
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Before processing the Upper-Layer header or any IPv6 extension header
other than Hop-by-Hop or Destination Option of a packet matching a
FIB entry locally instantiated as an End.B6.Encaps SID with the NEXT-
C-SID flavor:
N01. If (DA.Argument != 0) {
N02. If (IPv6 Hop Limit <= 1) {
N03. Send an ICMP Time Exceeded message to the Source Address,
Code 0 (Hop limit exceeded in transit),
interrupt packet processing and discard the packet.
N04. }
N05. Copy DA.Argument into the bits [LBL..(LBL+AL-1)] of the
Destination Address.
N06. Set the bits [(LBL+AL)..127] of the Destination Address to
zero.
N07. Decrement IPv6 Hop Limit by 1.
N08.1. Push a new IPv6 header with its own SRH containing B.
N08.2. Set the outer IPv6 SA to A.
N08.3. Set the outer IPv6 DA to the first SID of B.
N08.4. Set the outer Payload Length, Traffic Class, Flow Label,
Hop Limit, and Next Header fields.
N08.5. Submit the packet to the egress IPv6 FIB lookup for
transmission to the next destination.
N09. }
When processing the Upper-Layer header of a packet matching a FIB
entry locally instantiated as an End.B6.Encaps SID with the NEXT-
C-SID flavor:
S01. If (Upper-Layer header type is allowed by local configuration) {
S02. Proceed to process the Upper-Layer header
S03. } Else {
S04. Send an ICMP Parameter Problem to the Source Address
with Code 4 (SR Upper-layer Header Error)
and Pointer set to the offset of the Upper-Layer header,
interrupt packet processing, and discard the packet.
S05. }
A.5. End.BM with NEXT-C-SID
When processing the SRH of a packet matching a FIB entry locally
instantiated as an End.BM SID with the NEXT-C-SID flavor:
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N01. If (DA.Argument != 0) {
N02. If (IPv6 Hop Limit <= 1) {
N03. Send an ICMP Time Exceeded message to the Source Address,
Code 0 (Hop limit exceeded in transit),
interrupt packet processing and discard the packet.
N04. }
N05. Copy DA.Argument into the bits [LBL..(LBL+AL-1)] of the
Destination Address.
N06. Set the bits [(LBL+AL)..127] of the Destination Address to
zero.
N07. Decrement IPv6 Hop Limit by 1.
N08.1. Push the MPLS label stack for B.
N08.2. Submit the packet to the MPLS engine for transmission.
N09. }
S02. If (Segments Left == 0) {
S03. Stop processing the SRH, and proceed to process the next
header in the packet, whose type is identified by
the Next Header field in the routing header.
S04. }
S05. If (IPv6 Hop Limit <= 1) {
S06. Send an ICMP Time Exceeded message to the Source Address
with Code 0 (Hop limit exceeded in transit),
interrupt packet processing, and discard the packet.
S07. }
S08. max_LE = (Hdr Ext Len / 2) - 1
S09. If ((Last Entry > max_LE) or (Segments Left > Last Entry+1)) {
S10. Send an ICMP Parameter Problem to the Source Address
with Code 0 (Erroneous header field encountered)
and Pointer set to the Segments Left field,
interrupt packet processing, and discard the packet.
S11. }
S12. Decrement IPv6 Hop Limit by 1.
S13. Decrement Segments Left by 1.
S14. Update IPv6 DA with Segment List[Segments Left].
S15. Push the MPLS label stack for B.
S16. Submit the packet to the MPLS engine for transmission.
Before processing the Upper-Layer header or any IPv6 extension header
other than Hop-by-Hop or Destination Option of a packet matching a
FIB entry locally instantiated as an End.BM SID with the NEXT-C-SID
flavor:
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N01. If (DA.Argument != 0) {
N02. If (IPv6 Hop Limit <= 1) {
N03. Send an ICMP Time Exceeded message to the Source Address,
Code 0 (Hop limit exceeded in transit),
interrupt packet processing and discard the packet.
N04. }
N05. Copy DA.Argument into the bits [LBL..(LBL+AL-1)] of the
Destination Address.
N06. Set the bits [(LBL+AL)..127] of the Destination Address to
zero.
N07. Decrement IPv6 Hop Limit by 1.
N08.1. Push the MPLS label stack for B.
N08.2. Submit the packet to the MPLS engine for transmission.
N09. }
When processing the Upper-Layer header of a packet matching a FIB
entry locally instantiated as an End.BM SID with the NEXT-C-SID
flavor:
S01. If (Upper-Layer header type is allowed by local configuration) {
S02. Proceed to process the Upper-Layer header
S03. } Else {
S04. Send an ICMP Parameter Problem to the Source Address
with Code 4 (SR Upper-layer Header Error)
and Pointer set to the offset of the Upper-Layer header,
interrupt packet processing, and discard the packet.
S05. }
A.6. End with REPLACE-C-SID
When processing the SRH of a packet matching a FIB entry locally
instantiated as an End SID with the REPLACE-C-SID flavor:
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S01. When an SRH is processed {
S02. If (Segments Left == 0 and (DA.Arg.Index == 0 or
Segment List[0][DA.Arg.Index-1] == 0)) {
S03. Stop processing the SRH, and proceed to process the next
header in the packet, whose type is identified by
the Next Header field in the routing header.
S04. }
S05. If (IPv6 Hop Limit <= 1) {
S06. Send an ICMP Time Exceeded message to the Source Address,
Code 0 (Hop limit exceeded in transit),
interrupt packet processing and discard the packet.
S07. }
S08. max_LE = (Hdr Ext Len / 2) - 1
R01. If (DA.Arg.Index != 0) {
R02. If ((Last Entry > max_LE) or (Segments Left > Last Entry)) {
R03. Send an ICMP Parameter Problem to the Source Address,
Code 0 (Erroneous header field encountered),
Pointer set to the Segments Left field,
interrupt packet processing and discard the packet.
R04. }
R05. Decrement DA.Arg.Index by 1.
R06. If (Segment List[Segments Left][DA.Arg.Index] == 0) {
R07. Decrement Segments Left by 1.
R08. Decrement IPv6 Hop Limit by 1.
R09. Update IPv6 DA with Segment List[Segments Left]
R10. Submit the packet to the egress IPv6 FIB lookup for
transmission to the new destination.
R11. }
R12. } Else {
R13. If((Last Entry > max_LE) or (Segments Left > Last Entry+1)){
R14. Send an ICMP Parameter Problem to the Source Address,
Code 0 (Erroneous header field encountered),
Pointer set to the Segments Left field,
interrupt packet processing and discard the packet.
R15. }
R16. Decrement Segments Left by 1.
R17. Set DA.Arg.Index to (128/LNFL - 1).
R18. }
R19. Decrement IPv6 Hop Limit by 1.
R20. Write Segment List[Segments Left][DA.Arg.Index] into the bits
[LBL..LBL+LNFL-1] of the Destination Address of the IPv6
header.
R21. Submit the packet to the egress IPv6 FIB lookup for
transmission to the new destination.
S16. }
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When processing the Upper-Layer header of a packet matching a FIB
entry locally instantiated as an End SID with the REPLACE-C-SID
flavor:
S01. If (Upper-Layer header type is allowed by local configuration) {
S02. Proceed to process the Upper-Layer header
S03. } Else {
S04. Send an ICMP Parameter Problem to the Source Address
with Code 4 (SR Upper-layer Header Error)
and Pointer set to the offset of the Upper-Layer header,
interrupt packet processing, and discard the packet.
S05. }
A.7. End.X with REPLACE-C-SID
When processing the SRH of a packet matching a FIB entry locally
instantiated as an End.X SID with the REPLACE-C-SID flavor:
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S01. When an SRH is processed {
S02. If (Segments Left == 0 and (DA.Arg.Index == 0 or
Segment List[0][DA.Arg.Index-1] == 0)) {
S03. Stop processing the SRH, and proceed to process the next
header in the packet, whose type is identified by
the Next Header field in the routing header.
S04. }
S05. If (IPv6 Hop Limit <= 1) {
S06. Send an ICMP Time Exceeded message to the Source Address,
Code 0 (Hop limit exceeded in transit),
interrupt packet processing and discard the packet.
S07. }
S08. max_LE = (Hdr Ext Len / 2) - 1
R01. If (DA.Arg.Index != 0) {
R02. If ((Last Entry > max_LE) or (Segments Left > Last Entry)) {
R03. Send an ICMP Parameter Problem to the Source Address,
Code 0 (Erroneous header field encountered),
Pointer set to the Segments Left field,
interrupt packet processing and discard the packet.
R04. }
R05. Decrement DA.Arg.Index by 1.
R06. If (Segment List[Segments Left][DA.Arg.Index] == 0) {
R07. Decrement Segments Left by 1.
R08. Decrement IPv6 Hop Limit by 1.
R09. Update IPv6 DA with Segment List[Segments Left]
R10. Submit the packet to the IPv6 module for transmission to
the new destination via a member of J.
R11. }
R12. } Else {
R13. If((Last Entry > max_LE) or (Segments Left > Last Entry+1)){
R14. Send an ICMP Parameter Problem to the Source Address,
Code 0 (Erroneous header field encountered),
Pointer set to the Segments Left field,
interrupt packet processing and discard the packet.
R15. }
R16. Decrement Segments Left by 1.
R17. Set DA.Arg.Index to (128/LNFL - 1).
R18. }
R19. Decrement IPv6 Hop Limit by 1.
R20. Write Segment List[Segments Left][DA.Arg.Index] into the bits
[LBL..LBL+LNFL-1] of the Destination Address of the IPv6
header.
R21. Submit the packet to the IPv6 module for transmission to the
new destination via a member of J.
S16. }
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When processing the Upper-Layer header of a packet matching a FIB
entry locally instantiated as an End.X SID with the REPLACE-C-SID
flavor:
S01. If (Upper-Layer header type is allowed by local configuration) {
S02. Proceed to process the Upper-Layer header
S03. } Else {
S04. Send an ICMP Parameter Problem to the Source Address
with Code 4 (SR Upper-layer Header Error)
and Pointer set to the offset of the Upper-Layer header,
interrupt packet processing, and discard the packet.
S05. }
A.8. End.T with REPLACE-C-SID
When processing the SRH of a packet matching a FIB entry locally
instantiated as an End.T SID with the REPLACE-C-SID flavor:
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S01. When an SRH is processed {
S02. If (Segments Left == 0 and (DA.Arg.Index == 0 or
Segment List[0][DA.Arg.Index-1] == 0)) {
S03. Stop processing the SRH, and proceed to process the next
header in the packet, whose type is identified by
the Next Header field in the routing header.
S04. }
S05. If (IPv6 Hop Limit <= 1) {
S06. Send an ICMP Time Exceeded message to the Source Address,
Code 0 (Hop limit exceeded in transit),
interrupt packet processing and discard the packet.
S07. }
S08. max_LE = (Hdr Ext Len / 2) - 1
R01. If (DA.Arg.Index != 0) {
R02. If ((Last Entry > max_LE) or (Segments Left > Last Entry)) {
R03. Send an ICMP Parameter Problem to the Source Address,
Code 0 (Erroneous header field encountered),
Pointer set to the Segments Left field,
interrupt packet processing and discard the packet.
R04. }
R05. Decrement DA.Arg.Index by 1.
R06. If (Segment List[Segments Left][DA.Arg.Index] == 0) {
R07. Decrement Segments Left by 1.
R08. Decrement IPv6 Hop Limit by 1.
R09. Update IPv6 DA with Segment List[Segments Left]
R10.1. Set the packet's associated FIB table to T.
R10.2. Submit the packet to the egress IPv6 FIB lookup for
transmission to the new destination.
R11. }
R12. } Else {
R13. If((Last Entry > max_LE) or (Segments Left > Last Entry+1)){
R14. Send an ICMP Parameter Problem to the Source Address,
Code 0 (Erroneous header field encountered),
Pointer set to the Segments Left field,
interrupt packet processing and discard the packet.
R15. }
R16. Decrement Segments Left by 1.
R17. Set DA.Arg.Index to (128/LNFL - 1).
R18. }
R19. Decrement IPv6 Hop Limit by 1.
R20. Write Segment List[Segments Left][DA.Arg.Index] into the bits
[LBL..LBL+LNFL-1] of the Destination Address of the IPv6
header.
R21.1. Set the packet's associated FIB table to T.
R21.2. Submit the packet to the egress IPv6 FIB lookup for
transmission to the new destination.
S16. }
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When processing the Upper-Layer header of a packet matching a FIB
entry locally instantiated as an End.T SID with the REPLACE-C-SID
flavor:
S01. If (Upper-Layer header type is allowed by local configuration) {
S02. Proceed to process the Upper-Layer header
S03. } Else {
S04. Send an ICMP Parameter Problem to the Source Address
with Code 4 (SR Upper-layer Header Error)
and Pointer set to the offset of the Upper-Layer header,
interrupt packet processing, and discard the packet.
S05. }
A.9. End.B6.Encaps with REPLACE-C-SID
When processing the SRH of a packet matching a FIB entry locally
instantiated as an End.B6.Encaps SID with the REPLACE-C-SID flavor:
S01. When an SRH is processed {
S02. If (Segments Left == 0 and (DA.Arg.Index == 0 or
Segment List[0][DA.Arg.Index-1] == 0)) {
S03. Stop processing the SRH, and proceed to process the next
header in the packet, whose type is identified by
the Next Header field in the routing header.
S04. }
S05. If (IPv6 Hop Limit <= 1) {
S06. Send an ICMP Time Exceeded message to the Source Address,
Code 0 (Hop limit exceeded in transit),
interrupt packet processing and discard the packet.
S07. }
S08. max_LE = (Hdr Ext Len / 2) - 1
R01. If (DA.Arg.Index != 0) {
R02. If ((Last Entry > max_LE) or (Segments Left > Last Entry)) {
R03. Send an ICMP Parameter Problem to the Source Address,
Code 0 (Erroneous header field encountered),
Pointer set to the Segments Left field,
interrupt packet processing and discard the packet.
R04. }
R05. Decrement DA.Arg.Index by 1.
R06. If (Segment List[Segments Left][DA.Arg.Index] == 0) {
R07. Decrement Segments Left by 1.
R08. Decrement IPv6 Hop Limit by 1.
R09. Update IPv6 DA with Segment List[Segments Left]
R10.1. Push a new IPv6 header with its own SRH containing B.
R10.2. Set the outer IPv6 SA to A.
R10.3. Set the outer IPv6 DA to the first SID of B.
R10.4. Set the outer Payload Length, Traffic Class, Flow Label,
Hop Limit, and Next Header fields.
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R10.5. Submit the packet to the egress IPv6 FIB lookup for
transmission to the next destination.
R11. }
R12. } Else {
R13. If((Last Entry > max_LE) or (Segments Left > Last Entry+1)){
R14. Send an ICMP Parameter Problem to the Source Address,
Code 0 (Erroneous header field encountered),
Pointer set to the Segments Left field,
interrupt packet processing and discard the packet.
R15. }
R16. Decrement Segments Left by 1.
R17. Set DA.Arg.Index to (128/LNFL - 1).
R18. }
R19. Decrement IPv6 Hop Limit by 1.
R20. Write Segment List[Segments Left][DA.Arg.Index] into the bits
[LBL..LBL+LNFL-1] of the Destination Address of the IPv6
header.
R21.1. Push a new IPv6 header with its own SRH containing B.
R21.2. Set the outer IPv6 SA to A.
R21.3. Set the outer IPv6 DA to the first SID of B.
R21.4. Set the outer Payload Length, Traffic Class, Flow Label,
Hop Limit, and Next Header fields.
R21.5. Submit the packet to the egress IPv6 FIB lookup for
transmission to the next destination.
S16. }
When processing the Upper-Layer header of a packet matching a FIB
entry locally instantiated as an End.B6.Encaps SID with the REPLACE-
C-SID flavor:
S01. If (Upper-Layer header type is allowed by local configuration) {
S02. Proceed to process the Upper-Layer header
S03. } Else {
S04. Send an ICMP Parameter Problem to the Source Address
with Code 4 (SR Upper-layer Header Error)
and Pointer set to the offset of the Upper-Layer header,
interrupt packet processing, and discard the packet.
S05. }
A.10. End.BM with REPLACE-C-SID
When processing the SRH of a packet matching a FIB entry locally
instantiated as an End.BM SID with the REPLACE-C-SID flavor:
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S01. When an SRH is processed {
S02. If (Segments Left == 0 and (DA.Arg.Index == 0 or
Segment List[0][DA.Arg.Index-1] == 0)) {
S03. Stop processing the SRH, and proceed to process the next
header in the packet, whose type is identified by
the Next Header field in the routing header.
S04. }
S05. If (IPv6 Hop Limit <= 1) {
S06. Send an ICMP Time Exceeded message to the Source Address,
Code 0 (Hop limit exceeded in transit),
interrupt packet processing and discard the packet.
S07. }
S08. max_LE = (Hdr Ext Len / 2) - 1
R01. If (DA.Arg.Index != 0) {
R02. If ((Last Entry > max_LE) or (Segments Left > Last Entry)) {
R03. Send an ICMP Parameter Problem to the Source Address,
Code 0 (Erroneous header field encountered),
Pointer set to the Segments Left field,
interrupt packet processing and discard the packet.
R04. }
R05. Decrement DA.Arg.Index by 1.
R06. If (Segment List[Segments Left][DA.Arg.Index] == 0) {
R07. Decrement Segments Left by 1.
R08. Decrement IPv6 Hop Limit by 1.
R09. Update IPv6 DA with Segment List[Segments Left]
R10.1. Push the MPLS label stack for B.
R10.2. Submit the packet to the MPLS engine for transmission.
R11. }
R12. } Else {
R13. If((Last Entry > max_LE) or (Segments Left > Last Entry+1)){
R14. Send an ICMP Parameter Problem to the Source Address,
Code 0 (Erroneous header field encountered),
Pointer set to the Segments Left field,
interrupt packet processing and discard the packet.
R15. }
R16. Decrement Segments Left by 1.
R17. Set DA.Arg.Index to (128/LNFL - 1).
R18. }
R19. Decrement IPv6 Hop Limit by 1.
R20. Write Segment List[Segments Left][DA.Arg.Index] into the bits
[LBL..LBL+LNFL-1] of the Destination Address of the IPv6
header.
R21.1. Push the MPLS label stack for B.
R21.2. Submit the packet to the MPLS engine for transmission.
S16. }
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When processing the Upper-Layer header of a packet matching a FIB
entry locally instantiated as an End.BM SID with the REPLACE-C-SID
flavor:
S01. If (Upper-Layer header type is allowed by local configuration) {
S02. Proceed to process the Upper-Layer header
S03. } Else {
S04. Send an ICMP Parameter Problem to the Source Address
with Code 4 (SR Upper-layer Header Error)
and Pointer set to the offset of the Upper-Layer header,
interrupt packet processing, and discard the packet.
S05. }
Contributors
Liu Aihua
ZTE Corporation
China
Email: liu.aihua@zte.com.cn
Dennis Cai
Alibaba
United States of America
Email: d.cai@alibaba-inc.com
Darren Dukes
Cisco Systems, Inc.
Canada
Email: ddukes@cisco.com
James N Guichard
Futurewei Technologies Ltd.
United States of America
Email: james.n.guichard@futurewei.com
Cheng Li
Huawei Technologies
China
Email: c.l@huawei.com
Robert Raszuk
NTT Network Innovations
United States of America
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Email: robert@raszuk.net
Ketan Talaulikar
Cisco Systems, Inc.
India
Email: ketant.ietf@gmail.com
Daniel Voyer
Bell Canada
Canada
Email: daniel.voyer@bell.ca
Shay Zadok
Broadcom
Israel
Email: shay.zadok@broadcom.com
Authors' Addresses
Weiqiang Cheng (editor)
China Mobile
China
Email: chengweiqiang@chinamobile.com
Clarence Filsfils
Cisco Systems, Inc.
Belgium
Email: cf@cisco.com
Zhenbin Li
Huawei Technologies
China
Email: lizhenbin@huawei.com
Bruno Decraene
Orange
France
Email: bruno.decraene@orange.com
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Francois Clad (editor)
Cisco Systems, Inc.
France
Email: fclad.ietf@gmail.com
Cheng, et al. Expires 1 September 2024 [Page 74]
