



Internet Engineering Task Force (IETF)                         N. Nainar
Request for Comments: 8690                                  C. Pignataro
Updates: 8287                                        Cisco Systems, Inc.
Category: Standards Track                                       F. Iqbal
ISSN: 2070-1721                                               Individual
                                                           A. Vainshtein
                                                             ECI Telecom
                                                           December 2019


        Clarification of Segment ID Sub-TLV Length for RFC 8287

Abstract

   RFC 8287 defines the extensions to perform LSP Ping and Traceroute
   for Segment Routing IGP-Prefix and IGP-Adjacency Segment Identifiers
   (SIDs) with the MPLS data plane.  RFC 8287 proposes three Target
   Forwarding Equivalence Class (FEC) Stack sub-TLVs.  While RFC 8287
   defines the format and procedure to handle those sub-TLVs, it does
   not sufficiently clarify how the length of the Segment ID sub-TLVs
   should be computed to be included in the Length field of the sub-
   TLVs.  This ambiguity has resulted in interoperability issues.

   This document updates RFC 8287 by clarifying the length of each of
   the Segment ID sub-TLVs defined in RFC 8287.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8690.

Copyright Notice

   Copyright (c) 2019 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
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction
   2.  Terminology
   3.  Requirements Notation
   4.  Length Field Clarification for Segment ID Sub-TLVs
     4.1.  IPv4 IGP-Prefix Segment ID Sub-TLV
     4.2.  IPv6 IGP-Prefix Segment ID Sub-TLV
     4.3.  IGP-Adjacency Segment ID Sub-TLV
   5.  IANA Considerations
   6.  Security Considerations
   7.  Normative References
   Acknowledgements
   Contributors
   Authors' Addresses

1.  Introduction

   [RFC8287] defines the extensions to MPLS LSP Ping and Traceroute for
   Segment Routing IGP-Prefix and IGP-Adjacency Segment Identifiers
   (SIDs) with the MPLS data plane.  [RFC8287] proposes three Target FEC
   Stack sub-TLVs.  While RFC 8287 defines the format and procedure to
   handle those sub-TLVs, it does not sufficiently clarify how the
   length of the Segment ID sub-TLVs should be computed to be included
   in the Length field of the sub-TLVs, which may result in
   interoperability issues.

   This document updates [RFC8287] by clarifying the length of each
   Segment ID sub-TLVs defined in [RFC8287].

2.  Terminology

   This document uses the terminology defined in [RFC8402], [RFC8029],
   and [RFC8287]; readers are expected to be familiar with the terms as
   used in those documents.

3.  Requirements Notation

   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.

4.  Length Field Clarification for Segment ID Sub-TLVs

   Section 5 of [RFC8287] defines three different Segment ID sub-TLVs
   that can be included in the Target FEC Stack TLV defined in
   [RFC8029].  The length of each sub-TLV MUST be calculated as defined
   in this section.

   The TLV representations defined in Sections 5.1, 5.2, and 5.3 of
   [RFC8287] are updated to clarify the length calculations, as shown in
   Sections 4.1, 4.2, and 4.3, respectively.  The updated TLV
   representations contain explicitly defined lengths.

4.1.  IPv4 IGP-Prefix Segment ID Sub-TLV

   The sub-TLV length for the IPv4 IGP-Prefix Segment ID MUST be set to
   8, as shown in the TLV format below:

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |Type = 34 (IPv4 IGP-Prefix SID)|          Length = 8           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                          IPv4 prefix                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |Prefix Length  |    Protocol   |              Reserved         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

4.2.  IPv6 IGP-Prefix Segment ID Sub-TLV

   The sub-TLV length for the IPv6 IGP-Prefix Segment ID MUST be set to
   20, as shown in the TLV format below:

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |Type = 35 (IPv6 IGP-Prefix SID)|          Length = 20          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                                                               |
     |                                                               |
     |                       IPv6 Prefix                             |
     |                                                               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |Prefix Length  |    Protocol   |              Reserved         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

4.3.  IGP-Adjacency Segment ID Sub-TLV

   The sub-TLV length for the IGP-Adjacency Segment ID varies depending
   on the Adjacency Type and Protocol.  In any of the allowed
   combinations of Adjacency Type and Protocol, the sub-TLV length MUST
   be calculated by including 2 octets of the Reserved field.  Table 1
   lists the length for different combinations of Adj. Type and
   Protocol.

            +----------+-------------------------------------+
            | Protocol | Length for Adj. Type                |
            |          +----------+------+------+------------+
            |          | Parallel | IPv4 | IPv6 | Unnumbered |
            +==========+==========+======+======+============+
            |   OSPF   |    20    |  20  |  44  |     20     |
            +----------+----------+------+------+------------+
            |   ISIS   |    24    |  24  |  48  |     24     |
            +----------+----------+------+------+------------+
            |   Any    |    20    |  20  |  44  |     20     |
            +----------+----------+------+------+------------+

              Table 1: IGP-Adjacency SID Length Computation

   For example, when the Adj. Type is set to Parallel Adjacency and the
   Protocol is set to 0, the sub-TLV will be as below:

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |Type = 36 (IGP-Adjacency SID)  |          Length = 20          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Adj. Type = 1 | Protocol = 0  |          Reserved             |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |               Local Interface ID (4 octets)                   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |              Remote Interface ID (4 octets)                   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          Advertising Node Identifier (4 octets)               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |           Receiving Node Identifier (4 octets)                |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

5.  IANA Considerations

   IANA has listed this document as an additional reference for the
   following entries in the "Sub-TLVs for TLV Types 1, 16, and 21"
   registry:

      +----------+----------------------------+---------------------+
      | Sub-Type | Sub-TLV Name               | Reference           |
      +==========+============================+=====================+
      | 34       | IPv4 IGP-Prefix Segment ID | Section 5.1 of      |
      |          |                            | [RFC8287]; RFC 8690 |
      +----------+----------------------------+---------------------+
      | 35       | IPv6 IGP-Prefix Segment ID | Section 5.2 of      |
      |          |                            | [RFC8287]; RFC 8690 |
      +----------+----------------------------+---------------------+
      | 36       | IGP-Adjacency Segment ID   | Section 5.3 of      |
      |          |                            | [RFC8287]; RFC 8690 |
      +----------+----------------------------+---------------------+

      Table 2: Sub-TLVs for TLV Types 1, 16, and 21 (Updated Entries)

6.  Security Considerations

   This document updates [RFC8287] and does not introduce any additional
   security considerations.

7.  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>.

   [RFC8029]  Kompella, K., Swallow, G., Pignataro, C., Ed., Kumar, N.,
              Aldrin, S., and M. Chen, "Detecting Multiprotocol Label
              Switched (MPLS) Data-Plane Failures", RFC 8029,
              DOI 10.17487/RFC8029, March 2017,
              <https://www.rfc-editor.org/info/rfc8029>.

   [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>.

   [RFC8287]  Kumar, N., Ed., Pignataro, C., Ed., Swallow, G., Akiya,
              N., Kini, S., and M. Chen, "Label Switched Path (LSP)
              Ping/Traceroute for Segment Routing (SR) IGP-Prefix and
              IGP-Adjacency Segment Identifiers (SIDs) with MPLS Data
              Planes", RFC 8287, DOI 10.17487/RFC8287, December 2017,
              <https://www.rfc-editor.org/info/rfc8287>.

   [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>.

Acknowledgements

   The authors would like to thank Michael Gorokhovsky and Manohar
   Doppalapudi for investigating the interoperability issue during
   European Advanced Network Test Center (EANTC) testing.

Contributors

   The following individual contributed to this document: Zafar Ali,
   Cisco Systems, Inc.

Authors' Addresses

   Nagendra Kumar Nainar
   Cisco Systems, Inc.
   7200-12 Kit Creek Road
   Research Triangle Park, NC 27709
   United States of America

   Email: naikumar@cisco.com


   Carlos Pignataro
   Cisco Systems, Inc.
   7200-11 Kit Creek Road
   Research Triangle Park, NC 27709
   United States of America

   Email: cpignata@cisco.com


   Faisal Iqbal
   Individual
   Canada

   Email: faisal.ietf@gmail.com


   Alexander Vainshtein
   ECI Telecom
   Israel

   Email: vainshtein.alex@gmail.com
