SPRING W. Cheng, Ed. Internet-Draft China Mobile Intended status: Standards Track C. Filsfils Expires: 15 July 2023 Cisco Systems, Inc. Z. Li Huawei Technologies B. Decraene Orange F. Clad, Ed. Cisco Systems, Inc. 11 January 2023 Compressed SRv6 Segment List Encoding in SRH draft-ietf-spring-srv6-srh-compression-03 Abstract This document specifies new flavors for the SR endpoint behaviors defined in RFC 8986, which enable a compressed SRv6 Segment-List encoding in the Segment Routing Header (SRH). 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 15 July 2023. Copyright Notice Copyright (c) 2023 IETF Trust and the persons identified as the document authors. All rights reserved. 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 Cheng, et al. Expires 15 July 2023 [Page 1] Internet-Draft SRv6 Segment List Compression in SRH January 2023 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 . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1. Requirements Language . . . . . . . . . . . . . . . . . . 4 3. Basic Concepts . . . . . . . . . . . . . . . . . . . . . . . 4 4. SR Endpoint Flavors . . . . . . . . . . . . . . . . . . . . . 5 4.1. NEXT-C-SID Flavor . . . . . . . . . . . . . . . . . . . . 5 4.1.1. End with NEXT-C-SID . . . . . . . . . . . . . . . . . 6 4.1.2. End.X with NEXT-C-SID . . . . . . . . . . . . . . . . 7 4.1.3. Combination with PSP, USP and USD flavors . . . . . . 7 4.2. REPLACE-C-SID Flavor . . . . . . . . . . . . . . . . . . 7 4.2.1. End with REPLACE-C-SID . . . . . . . . . . . . . . . 8 4.2.2. End.X with REPLACE-C-SID . . . . . . . . . . . . . . 9 4.2.3. Combination with PSP, USP, and USD flavors . . . . . 9 4.3. Combined NEXT-and-REPLACE-C-SID Flavor . . . . . . . . . 10 5. C-SID Allocation . . . . . . . . . . . . . . . . . . . . . . 11 5.1. Global C-SID . . . . . . . . . . . . . . . . . . . . . . 12 5.2. Local C-SID . . . . . . . . . . . . . . . . . . . . . . . 12 6. C-SID and Locator-Block Length . . . . . . . . . . . . . . . 12 6.1. C-SID Length . . . . . . . . . . . . . . . . . . . . . . 12 6.2. Locator-Block Length . . . . . . . . . . . . . . . . . . 13 6.3. GIB/LIB Usage . . . . . . . . . . . . . . . . . . . . . . 13 7. Efficient SID-list Encoding . . . . . . . . . . . . . . . . . 14 8. Inter Routing Domains with the End.XPS behavior . . . . . . . 14 9. Control Plane . . . . . . . . . . . . . . . . . . . . . . . . 16 10. Operational Considerations . . . . . . . . . . . . . . . . . 16 10.1. Ping a SID without a Segment List . . . . . . . . . . . 16 10.2. Ping a SID via a Segment List . . . . . . . . . . . . . 16 10.3. ICMP Error Processing . . . . . . . . . . . . . . . . . 16 11. Illustrations . . . . . . . . . . . . . . . . . . . . . . . . 17 12. Deployment Model . . . . . . . . . . . . . . . . . . . . . . 17 13. Implementation Status . . . . . . . . . . . . . . . . . . . . 17 13.1. Cisco Systems . . . . . . . . . . . . . . . . . . . . . 18 13.2. Huawei Technologies . . . . . . . . . . . . . . . . . . 18 13.3. Open Source . . . . . . . . . . . . . . . . . . . . . . 19 13.4. Interoperability Report . . . . . . . . . . . . . . . . 19 14. Security Considerations . . . . . . . . . . . . . . . . . . . 21 15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21 15.1. SRv6 Endpoint Behaviors . . . . . . . . . . . . . . . . 21 16. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 23 17. References . . . . . . . . . . . . . . . . . . . . . . . . . 23 17.1. Normative References . . . . . . . . . . . . . . . . . . 23 Cheng, et al. Expires 15 July 2023 [Page 2] Internet-Draft SRv6 Segment List Compression in SRH January 2023 17.2. Informative References . . . . . . . . . . . . . . . . . 23 Appendix A. Open Issues . . . . . . . . . . . . . . . . . . . . 26 Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 28 1. Introduction The Segment Routing (SR) architecture and SR for IPv6 (SRv6) are defined in [RFC8402]. 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]. This document specifies new flavors to the SR endpoint behaviors defined in Section 4 of [RFC8986]. These flavors enable a compressed encoding of the SRv6 Segment-List in the SRH and therefore address the requirements described in [I-D.srcompdt-spring-compression-requirement]. 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 [I-D.ietf-lsr-isis-srv6-extensions], OSPF [I-D.ietf-lsr-ospfv3-srv6-extensions], and BGP [I-D.ietf-bess-srv6-services]. 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 SRv6 SID block (IPv6 prefix allocated for SRv6 SIDs by the operator) of an SRv6 SID Locator, as defined in Section 3.1 of [RFC8986]. * Locator-Node: The identifier of the parent node instantiating a SID in an SRv6 SID Locator, as defined in Section 3.1 of [RFC8986]. * Compressed-SID (C-SID): The Locator-Node and Function bits of a SID that supports compressed encoding of SIDs. * C-SID container: A 128-bit container holding a list of C-SIDs. Cheng, et al. Expires 15 July 2023 [Page 3] Internet-Draft SRv6 Segment List Compression in SRH January 2023 * C-SID sequence: A group of one or more consecutive C-SID containers in a segment list. * Uncompressed SID sequence: A group of one or more 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 may contain any number of uncompressed SID sequences. 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. 3. Basic Concepts In an SRv6 domain, the SIDs are allocated from a particular IPv6 prefix: the Locator-Block. All SRv6 SIDs instantiated from the same Locator-Block share the same most significant bits. When the combined length of the SRv6 SID Locator, Function, and Argument is smaller than 128 bits, the trailing bits are set to zero. When a sequence of consecutive SIDs in a Segment List shares a common Locator-Block, a compressed Segment-List encoding can optimize the packet header length by avoiding the repetition of the Locator-Block and trailing bits with each individual SID. The compressed Segment List encoding is fully compliant with the specifications in [RFC8402], [RFC8754], and [RFC8986]. Efficient encoding is achieved by combining a compressed Segment List encoding logic on the SR policy headend with new flavors of the base SRv6 endpoint behaviors that decode this compressed encoding. 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 Policy headend constructs and compresses the SID-list depending on the capabilities of each SR endpoint node that the packet should traverse, as well as its own compression capabilities. Cheng, et al. Expires 15 July 2023 [Page 4] Internet-Draft SRv6 Segment List Compression in SRH January 2023 It is expected that compressed encoding flavors be available on devices with limited packet manipulation capabilities, such as legacy ASICs. The compressed Segment List encoding supports any Locator-Block allocation. While other options are supported and may provide higher efficiency, each routing domain can be allocated a /48 prefix from a global IPv6 block (see Section 6.2). 4. SR Endpoint Flavors This section defines several options to achieve compressed Segment List encoding in the form of two new flavors for the End, End.X, and End.T behaviors of [RFC8986]. These flavors could also be combined with behaviors defined in other documents. The compressed encoding can be achieved by leveraging any of these SR endpoint flavors. The NEXT-C-SID flavor and the REPLACE-C-SID flavor expose the same high-level behavior in their use of the SID argument to determine the next segment to be processed, but they have different low-level characteristics that can make one more or less efficient than the other for a particular SRv6 deployment. The NEXT- and-REPLACE-C-SID flavor is the combination of the NEXT-C-SID flavor and the REPLACE-C-SID flavor. It provides the best efficiency in terms of encapsulation size at the cost of increased complexity. It is RECOMMENDED, for ease of operation, that a single compressed encoding flavor be used in a given SRv6 domain. However, in a multi- domain deployment, different flavors can be used in different domains. All three flavors leverage the following variables: * Variable B is the Locator-Block length of the SID. * Variable NF is the sum of the Locator-Node and the Function lengths of the SID. It is also referred to as C-SID length. * Variable A is the Argument length of the SID. 4.1. NEXT-C-SID Flavor A SID instantiated with the NEXT-C-SID flavor takes an argument that carries the remaining C-SIDs in the current C-SID container. The length A of the argument is equal to 128-B-NF and should be a multiple of NF. Cheng, et al. Expires 15 July 2023 [Page 5] Internet-Draft SRv6 Segment List Compression in SRH January 2023 +------------------------------------------------------------------+ | Locator-Block |Loc-Node| Argument | | |Function| | +------------------------------------------------------------------+ <--------- B ----------> <- NF -> <------------- A --------------> Figure 1: Example of a NEXT-C-SID flavored SID structure using a 48-bit Locator-Block, 16-bit combined locator and function, and 64-bit argument 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], and a second time before line S01 of the upper-layer header processing in Section 4.1.1 of [RFC8986], or prior to processing any extension header other than Hop-by-Hop or Destination Option. S01. If (DA.Argument != 0) { S02. If (IPv6 Hop Limit <= 1) { S03. Send an ICMP Time Exceeded message to the Source Address, Code 0 (Hop limit exceeded in transit), interrupt packet processing and discard the packet. S04. } S05. Copy the value of DA.Argument into the bits [B..(B+A-1)] of the Destination Address. S06. Set the bits [(B+A)..127] of the Destination Address to zero. S07. Decrement Hop Limit by 1. S08. Submit the packet to the egress IPv6 FIB lookup for transmission to the next destination. S09. } Notes: * DA.Argument identifies the bits [(B+NF)..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. Cheng, et al. Expires 15 July 2023 [Page 6] Internet-Draft SRv6 Segment List Compression in SRH January 2023 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 same modifications as in Section 4.1.1 of this document, except for line S08 that is replaced as follows. S08. Submit the packet to the IPv6 module for transmission to the new destination via a member of J. 4.1.3. 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 USD flavor is unchanged when combined with the NEXT-C-SID flavor. The pseudocodes defined in Section 4.1.1 and Section 4.1.2 of this document are inserted at the beginning of the modified upper- layer header processing defined in Section 4.16.3 of [RFC8986] for End and End.X, respectively. 4.2. REPLACE-C-SID Flavor A SID instantiated with the REPLACE-C-SID flavor takes an argument that indicates the index of the next C-SID in the appropriate C-SID container. The length A of the argument should be at least ceil(log_2(128/NF)). All SIDs that are part of a C-SID sequence using the REPLACE-C-SID flavor have the same C-SID length NF. +-------------------------------------------------------------------+ | Locator-Block | Locator-Node |Argument| 0 | | | + Function | | | +-------------------------------------------------------------------+ <--------- B ----------> <----- NF -----> <- A --> Figure 2: Example of a REPLACE-C-SID flavored SID structure using a 48-bit Locator-Block, 32-bit combined locator and function, and 16-bit argument Cheng, et al. Expires 15 July 2023 [Page 7] Internet-Draft SRv6 Segment List Compression in SRH January 2023 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 replaced as follows. S01. When an SRH is processed { S02. If (Segments Left == 0 and DA.Argument == 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 S09. If (DA.Argument != 0) { S10. If ((Last Entry > max_LE) or (Segments Left > Last Entry)) { S11. 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. S12. } S13. Decrement DA.Argument by 1. S14. } Else { S15. If((Last Entry > max_LE) or (Segments Left > Last Entry+1)){ S16. 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. S17. } S18. Decrement Segments Left by 1. S19. Set DA.Argument to (128/NF - 1). S20. } S21. Decrement IPv6 Hop Limit by 1 S22. Write Segment List[Segments Left][DA.Argument] into the bits [B..B+NF-1] of the Destination Address of the IPv6 header. S23. Submit the packet to the egress IPv6 FIB lookup for transmission to the new destination. S24. } Notes: * DA.Argument identifies the bits [(B+NF)..(B+NF+A-1)] in the Destination Address of the IPv6 header. Cheng, et al. Expires 15 July 2023 [Page 8] Internet-Draft SRv6 Segment List Compression in SRH January 2023 * Segment List[Segments Left][DA.Argument] identifies the bits [DA.Argument*NF..(DA.Argument+1)*NF-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. 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 same modifications as in Section 4.2.1 of this document, except for line S23 that is replaced as follows. S23. Submit the packet to the IPv6 module for transmission to the new destination via a member of J. 4.2.3. 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 line S22 of the pseudocode in Section 4.2.1, and the first line of the inserted instructions is modified as follows. S22.1. If (Segments Left == 0 and (DA.Argument == 0 or Segment List[Segments Left][DA.Argument-1] == 0)) { Note: * Segment List[Segments Left][DA.Argument-1] identifies the bits [(DA.Argument-1)*NF..DA.Argument*NF-1] in the SRH Segment List entry at index Segments Left. USP: When combined with the REPLACE-C-SID flavor, the lines S02-S04 of the pseudocode in Section 4.2.1 are substituted by the USP flavor instructions defined in Section 4.16.2 of [RFC8986], with the following modification. S02. If (Segments Left == 0 and DA.Argument == 0) { USD: The USD flavor defined in Section 4.16.3 of [RFC8986] is unchanged when combined with the REPLACE-C-SID flavor. Cheng, et al. Expires 15 July 2023 [Page 9] Internet-Draft SRv6 Segment List Compression in SRH January 2023 4.3. Combined NEXT-and-REPLACE-C-SID Flavor A SID instantiated with the NEXT-and-REPLACE-C-SID flavor takes a two-parts argument comprising, Arg.Next and Arg.Index, and encoded in the SID in this order. The length A_I of Arg.Index should be at least ceil(log_2(128/NF)). The length A_N of Arg.Next is equal to 128-B-NF-A_I and must be a multiple of NF. The total SID argument length A is the sum of A_I and A_N. The NEXT-and-REPLACE-C-SID flavor also leverages an additional variable, C_DA, that is equal to (1 + (A_N/NF)) and represents the number of C-SIDs that can be encoded in the IPv6 Destination Address. All SIDs that are part of a C-SID sequence using the NEXT-and- REPLACE-C-SID flavor must have the same C-SID length NF. Furthermore, this NF must be a divisor of 128. +-------------------------------------------------------------------+ | Locator-Block |Loc-Node| Arg.Next | Arg. | | |Function| | Index | +-------------------------------------------------------------------+ <--------- B ----------> <- NF -> <-------- A_N ---------> <- A_I -> Figure 3: Example of a NEXT-and-REPLACE-C-SID flavored SID structure using a 48-bit Locator-Block, 16-bit combined locator and function, 48-bit Arg.Next and 16-bit Arg.Index Pseudo-code: Cheng, et al. Expires 15 July 2023 [Page 10] Internet-Draft SRv6 Segment List Compression in SRH January 2023 1. If (DA.Arg.Next != 0) { 2. Copy DA.Arg.Next into the bits [B..(B+A_N-1)] of the Destination Address of the IPv6 header. 3. Set the bits [(B+A_N)..(B+NF+A_N-1)] of the Destination Address of the IPv6 header to zero. 4. } Else If (DA.Arg.Index >= C_DA) { 5. Decrement DA.Arg.Index by C_DA. 6. Copy C_DA*NF bits from Segment List[Segments Left][DA.Arg.Index] into the bits [B..B+C_DA*NF-1] of the Destination Address of the IPv6 header. 7. } Else If (Segments Left != 0) { 8. Decrement Segments Left by 1. 9. Set DA.Arg.Index to ((DA.Arg.Index - C_DA) % (128/NF)). 10. Copy C_DA*NF bits from Segment List[Segments Left][DA.Arg.Index] into the bits [B..B+C_DA*NF-1] of the Destination Address of the IPv6 header. 11. } Else { 12. Copy DA.Arg.Index*NF bits from Segment List[0][0] into the bits [B..B+DA.Arg.Index*NF-1] of the Destination Address of the IPv6 header. 13. Set the bits [B+DA.Arg.Index*NF..B+NF+A_N-1] of the Destination Address of the IPv6 header to zero. 14. Set DA.Arg.Index to 0. 15. } Notes: * DA.Arg.Next identifies the bits [(B+NF)..(B+NF+A_N-1)] in the Destination Address of the IPv6 header. * DA.Arg.Index identifies the bits [(B+NF+A_N)..(B+NF+A_N+A_I-1)] in the Destination Address of the IPv6 header. * Segment List[Segments Left][DA.Arg.Index] identifies the bits [DA.Arg.Index*NF..(DA.Arg.Index+1)*NF-1] in the SRH Segment List entry at index Segments Left. 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, it may be beneficial to divide it into two non-overlapping sub-spaces: a Global Identifiers Block (GIB) and a Local Identifiers Block (LIB). Cheng, et al. Expires 15 July 2023 [Page 11] Internet-Draft SRv6 Segment List Compression in SRH January 2023 * The GIB is the pool of C-SID values available for global allocation. * The LIB is the pool of C-SID values available for local allocation. 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 sup-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 Section 6.3. 5.1. Global C-SID A C-SID from the GIB. A Global C-SID typically identifies a shortest path to a node in the SRv6 domain. An IP route is advertised by the parent node to each of its global C-SIDs, under the associated Locator-Block. The parent node executes a variant of the End behavior. A node can have multiple global C-SIDs under the same Locator-Block (e.g., one per IGP flexible algorithm). Multiple nodes may share the same global C-SID (anycast). 5.2. Local C-SID A C-SID from the LIB. A local C-SID may identify a cross-connect to a direct neighbor over a specific interface or a VPN context. No IP route is advertised by a parent node for its local C-SIDs. If N1 and N2 are two different physical nodes of the SRv6 domain and I is a local C-SID value, then N1 and N2 may bind two different behaviors to I. 6. C-SID and Locator-Block Length 6.1. C-SID Length The NEXT-C-SID flavor supports both 16- and 32-bit C-SID lengths. A C-SID length of 16-bit is RECOMMENDED. Cheng, et al. Expires 15 July 2023 [Page 12] Internet-Draft SRv6 Segment List Compression in SRH January 2023 The REPLACE-C-SID flavor supports both 16- and 32-bit C-SID lengths. A C-SID length of 32-bit is RECOMMENDED. 6.2. Locator-Block Length The RECOMMENDED Locator-Block sizes for the NEXT-C-SID flavor are 16, 32, or 48 bits. The smaller the block, the higher the compression efficiency. The RECOMMENDED Locator-Block size for the REPLACE-C-SID flavor can be 48, 56, 64, 72, or 80 bits, depending on the needs of the operator. 6.3. 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 segment endpoint nodes using SRv6 locators under a Block space. The more SIDs assigned from this space, per node, the faster it is exhausted. Therefore its use is prioritized for SIDs that identify a node, like End behavior SIDs. 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 SIDs that identify services (of which there may be many) at nodes, like cross-connects, adjacencies, etc. While a longer C-SID length permits more flexibility in which SID behaviors may be assigned from the GIB, it also reduces compression. Given the previous Locator-Block and C-SID length recommendations, the following GIB/LIB usage is RECOMMENDED: * NEXT-C-SID: - GIB: End, End.T - LIB: End.X, 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 Cheng, et al. Expires 15 July 2023 [Page 13] Internet-Draft SRv6 Segment List Compression in SRH January 2023 - LIB: End.DX2/2V for large-scale pseudowire 7. Efficient SID-list Encoding The compressed SID-list encoding logic is a local behavior of the SR Policy headend node and hence out of the scope of this document. 8. Inter Routing Domains with the End.XPS behavior The End.XPS behavior described in this section is OPTIONAL. Some SRv6 traffic may need to cross multiple routing domains, such as different Autonomous Systems (ASes) or different routing areas. Different routing domains may use different addressing schema and Locator-Blocks. This section defines an optional solution and SID behavior allowing for the use of different Locator-Blocks between routing domains. The solution requires a new SID behavior, called "Endpoint with cross-connect to an array of layer-3 adjacencies and SRv6 Prefix Swap" (End.XPS for short) allowing for this transition of Locator- Block between two routing domains. End.XPS is a variant of End.X, performing both "End.X Layer-3 Cross- Connect" and the translation of the Locator-Block between the two routing domains. The processing takes as an additional parameter the prefix B2/m corresponding the Locator-Block in the second domain. This parameter is a property of the (received) SID and is given as a result of the lookup on the IPv6 destination address which identifies the SRv6 SID and its properties. The End.XPS behavior is compatible with the NEXT-C-SID, REPLACE- C-SID, and NEXT-and-REPLACE-C-SID flavors described in this document. When a router R receives a packet whose IPv6 DA matches a local End.XPS SID with the NEXT-C-SID flavor, that is associated with a set J of one or more Layer-3 adjacencies and the Locator-Block B2/m of the neighbor routing domain, R processes the packet as follows. Cheng, et al. Expires 15 July 2023 [Page 14] Internet-Draft SRv6 Segment List Compression in SRH January 2023 1. If (DA.Argument != 0) { 2. Write B2 into the most significant bits of the Destination Address of the IPv6 header. 3. Write DA.Argument into the bits [m..(m+A-1)] of the Destination Address of the IPv6 header. 4. Set the bits [(m+A)..127] of the Destination Address of the IPv6 header to zero. 5. } Else { 6. Decrement Segments Left by 1. 7. Copy Segment List[Segments Left] from the SRH to the Destination Address of the IPv6 header. 8. } 9. Submit the packet to the IPv6 module for transmission to the new destination via a member of J. When a router R receives a packet whose IPv6 DA matches a local End.XPS SID with the REPLACE-C-SID flavor, that is associated with a set J of one or more Layer-3 adjacencies and the Locator-Block B2/m of the neighbor routing domain, R processes the packet as follows. 1. If (DA.Argument != 0) { 2. Decrement DA.Argument by 1. 3. } Else { 4. Decrement Segments Left by 1. 5. Set DA.Argument to (128/NF - 1). 6. } 7. Write B2 into the most significant bits of the Destination Address of the IPv6 header. 8. Write Segment List[Segments Left][DA.Argument] into the bits [m..m+NF-1] of the Destination Address of the IPv6 header. 9. Write DA.Argument into the bits [m+NF..m+NF+A-1] of the Destination Address of the IPv6 header. 10. Set the bits [(m+NF+A)..127] of the Destination Address of the IPv6 header to zero. 11. Submit the packet to the IPv6 module for transmission to the new destination via a member of J. Note: the way the Locator-Block B2 of the next routing domain is known is out of scope of this document. As examples, it could be learnt via configuration, or using a signaling protocol either with the peer domain or with a central controller (e.g. Path Computation Element (PCE)). When End.XPS SID behavior is used, the restriction on the C-SID length for the REPLACE-C-SID and the NEXT-and-REPLACE-C-SID flavors is relaxed and becomes: all SID the are part of a C-SID sequence *within a domain* MUST have the same SID length NF. Cheng, et al. Expires 15 July 2023 [Page 15] Internet-Draft SRv6 Segment List Compression in SRH January 2023 9. Control Plane This document does not require any control plane modification. 10. Operational Considerations 10.1. Ping a SID without a Segment List An SR source node may ping a routable SRv6 SID by sending an ICMPv6 echo request packet destined to the SRv6 SID, as illustrated in Appendix A.1.2 of [RFC9259]. When the SRv6 SID in the destination address of the ICMPv6 echo request is one of the SID flavors defined in this document, the SR source node MUST set the arguments of the SID to 0. 10.2. Ping a SID via a Segment List An SR source node may ping a routable or non-routable SRv6 SID via a segment list as illustrated in Appendix A.1.2 of [RFC9259]. Regardless of the behavior of the SIDs in the SID list, the SR source node computes the ICMP echo request checksum using the ultimate segment in the segment list, i.e., the IPv6 destination address as it is expected to appear at the final destination of the packet. 10.3. 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 should follow 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. Cheng, et al. Expires 15 July 2023 [Page 16] Internet-Draft SRv6 Segment List Compression in SRH January 2023 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. 11. Illustrations Illustrations for the functionalities defined in this document are provided in [I-D.clad-spring-srv6-srh-compression-illus]. 12. Deployment Model Section 5 of [RFC8754] defines the intra-SR-domain deployment model and associated security procedures. The same deployment model applies to the SIDs defined in this document. 13. Implementation Status This section is to be removed before publishing as an RFC. 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]). Cheng, et al. Expires 15 July 2023 [Page 17] Internet-Draft SRv6 Segment List Compression in SRH January 2023 13.1. Cisco Systems Cisco Systems reported the following implementations of the SR endpoint node NEXT-C-SID flavor (Section 4.1) for NEXT-C-SID flavored 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] 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. 13.2. Huawei Technologies Huawei Technologies reported the following implementations of the SR endpoint node REPLACE-C-SID flavor (Section 4.2) for REPLACE-C-SID flavored SIDs. 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. Cheng, et al. Expires 15 July 2023 [Page 18] Internet-Draft SRv6 Segment List Compression in SRH January 2023 * 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. 13.3. Open Source The authors found the following open source implementations of the SR 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] * A generic P4 implementation [IMPL-OSS-P4] The authors found the following open source implementations of the SR 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. 13.4. Interoperability Report 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 Cheng, et al. Expires 15 July 2023 [Page 19] Internet-Draft SRv6 Segment List Compression in SRH January 2023 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 "", where S1..S7 are SIDs instantiated on SR segment endpoint nodes N1..N7, respectively. 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 segment endpoint 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 Cheng, et al. Expires 15 July 2023 [Page 20] Internet-Draft SRv6 Segment List Compression in SRH January 2023 * The SR source node imposes a compressed segment list encoding of 2 SIDs. *Scenario 3:* * 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. 14. Security Considerations The security requirements and mechanisms described in [RFC8402] and [RFC8754] also apply to this document. This document does not introduce any new security considerations. 15. IANA Considerations 15.1. SRv6 Endpoint Behaviors This I-D. requests IANA to make the following registrations from the "SRv6 Endpoint Behaviors" sub-registry under the top-level "Segment Routing" registry (https://www.iana.org/assignments/segment- routing/): +-------+-----------------------------------------+-----------+ | 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. | +-------+-----------------------------------------+-----------+ Cheng, et al. Expires 15 July 2023 [Page 21] Internet-Draft SRv6 Segment List Compression in SRH January 2023 | 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. | +-------+-----------------------------------------+-----------+ | 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. | +-------+-----------------------------------------+-----------+ | 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. | +-------+-----------------------------------------+-----------+ | 128 | End with REPLACE-CSID & USD | This I-D. | +-------+-----------------------------------------+-----------+ | 129 | End with REPLACE-CSID, USP & USD | This I-D. | +-------+-----------------------------------------+-----------+ | 130 | End with REPLACE-CSID, PSP & USD | This I-D. | +-------+-----------------------------------------+-----------+ | 131 | End with REPLACE-CSID, PSP, USP & USD | This I-D. | +-------+-----------------------------------------+-----------+ | 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. | +-------+-----------------------------------------+-----------+ Table 1: Registration List Cheng, et al. Expires 15 July 2023 [Page 22] Internet-Draft SRv6 Segment List Compression in SRH January 2023 16. Acknowledgements The authors would like to thank Kamran Raza, Xing Jiang, YuanChao Su, Han Li and Yisong Liu. 17. References 17.1. 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, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [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, . [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, . [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, . 17.2. Informative References [EMAIL1] "SPRING chairs email on the adoption of draft- filsfilscheng-spring-srv6-srh-compression-02", October 2021, . [EMAIL2] "SPRING chairs email on working group process", February 2022, . [I-D.clad-spring-srv6-srh-compression-illus] Clad, F. and D. Dukes, "Illustrations for Compressed SRv6 Segment List Encoding in SRH", Work in Progress, Internet- Cheng, et al. Expires 15 July 2023 [Page 23] Internet-Draft SRv6 Segment List Compression in SRH January 2023 Draft, draft-clad-spring-srv6-srh-compression-illus-02, 24 October 2022, . [I-D.ietf-bess-srv6-services] Dawra, G., Talaulikar, K., Raszuk, R., Decraene, B., Zhuang, S., and J. Rabadan, "BGP Overlay Services Based on Segment Routing over IPv6 (SRv6)", Work in Progress, Internet-Draft, draft-ietf-bess-srv6-services-15, 22 March 2022, . [I-D.ietf-lsr-isis-srv6-extensions] Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and Z. Hu, "IS-IS Extensions to Support Segment Routing over IPv6 Dataplane", Work in Progress, Internet-Draft, draft- ietf-lsr-isis-srv6-extensions-19, 14 November 2022, . [I-D.ietf-lsr-ospfv3-srv6-extensions] Li, Z., Hu, Z., Talaulikar, K., and P. Psenak, "OSPFv3 Extensions for SRv6", Work in Progress, Internet-Draft, draft-ietf-lsr-ospfv3-srv6-extensions-08, 14 September 2022, . [I-D.srcompdt-spring-compression-requirement] Cheng, W., Xie, C., Bonica, R., Dukes, D., Li, C., Peng, S., and W. Henderickx, "Compressed SRv6 SID List Requirements", Work in Progress, Internet-Draft, draft- srcompdt-spring-compression-requirement-07, 11 July 2021, . [IMPL-CISCO-8000] Cisco Systems, "Segment Routing Configuration Guide for Cisco 8000 Series Routers", 4 November 2022, . [IMPL-CISCO-ASR9000] Cisco Systems, "Segment Routing Configuration Guide for Cisco ASR 9000 Series Routers", 6 November 2022, . [IMPL-CISCO-NCS540] Cisco Systems, "Segment Routing Configuration Guide for Cisco NCS 540 Series Routers", 2 November 2022, . [IMPL-CISCO-NCS5500] Cisco Systems, "Segment Routing Configuration Guide for Cisco NCS 5500 Series Routers", 6 November 2022, . [IMPL-CISCO-NCS560] Cisco Systems, "Segment Routing Configuration Guide for Cisco NCS 560 Series Routers", 14 October 2022, . [IMPL-CISCO-NCS5700] Cisco Systems, "Segment Routing Configuration Guide for Cisco NCS 5700 Series Routers", 6 November 2022, . [IMPL-OSS-LINUX] Abeni, P., "Add NEXT-C-SID support for SRv6 End behavior", 20 September 2022, . [IMPL-OSS-ONOS] Open Networking Foundation, "Stratum CMCC G-SRv6 Project", 24 March 2021, . [IMPL-OSS-OPEN-SRV6] "Open SRv6 Project", n.d., . Cheng, et al. Expires 15 July 2023 [Page 25] Internet-Draft SRv6 Segment List Compression in SRH January 2023 [IMPL-OSS-P4] Salsano, S. and A. Tulumello, "SRv6 uSID (micro SID) implementation on P4", 3 January 2021, . [IMPL-OSS-SAI] Agrawal, A., "Added new behaviors to support uSID instruction", 8 June 2021, . [IMPL-OSS-SONIC] Shah, S. and R. Sudarshan, "SONiC uSID", 21 August 2022, . [IMPL-OSS-VPP] FD.io, "Srv6 cli reference", n.d., . [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, . [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, . [SPRING-WG-POLICIES] SPRING Working Group Chairs, "SPRING Working Group Policies", 14 October 2022, . Appendix A. Open Issues This section was added as requested by the SPRING chair in [EMAIL1]. Issues raised during and after the adoption call for this draft are tracked in an issue tracker. The remainder of this section identifies the most significant open issues, from the adoption call, for the working group to keep track of. As a reminder to those reading this section, this document is a work in progress, and subject to change by the working group. As noted at Cheng, et al. Expires 15 July 2023 [Page 26] Internet-Draft SRv6 Segment List Compression in SRH January 2023 the front of this document, "It is inappropriate to use Internet- Drafts as reference material" * Given that the working group has said that it wants to standardize one data plane solution, and given that the document contains multiple SRv6 EndPoint behaviors that some WG members have stated are multiple data plane solutions, the working group will address whether this is valid and coherent with its one data plane solution objective. * As reminded in the conclusion of the adoption call, this document is subject to the policy announced by the SPRING chairs in [EMAIL2]. In particular, this means that this document can not go to WG last call until 6man completes handling of an Internet Draft that deals with the relationship of C-SIDs to RFC 4291. It is hoped and expected that said resolution will be a WG last call and document approval in 6man of a document providing for the way that C-SIDs use the IPv6 destination address field. 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, et al. Expires 15 July 2023 [Page 27] Internet-Draft SRv6 Segment List Compression in SRH January 2023 Cheng Li Huawei Technologies China Email: chengli13@huawei.com Robert Raszuk NTT Network Innovations United States of America Email: robert@raszuk.net 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 Cheng, et al. Expires 15 July 2023 [Page 28] Internet-Draft SRv6 Segment List Compression in SRH January 2023 Email: lizhenbin@huawei.com Bruno Decraene Orange France Email: bruno.decraene@orange.com Francois Clad (editor) Cisco Systems, Inc. France Email: fclad@cisco.com Cheng, et al. Expires 15 July 2023 [Page 29]