Clarification of Segment ID Sub-TLV Length for RFC 8287
RFC 8690

Document Type RFC - Proposed Standard (December 2019; No errata)
Updates RFC 8287
Last updated 2019-12-11
Replaces draft-nainar-mpls-rfc8287-len-clarification
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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
   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 Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   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
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