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IS-IS Extensions to Support Segment Routing over the IPv6 Data Plane
RFC 9352

Document Type RFC - Proposed Standard (February 2023)
Updates RFC 7370
Authors Peter Psenak , Clarence Filsfils , Ahmed Bashandy , Bruno Decraene , Zhibo Hu
Last updated 2023-12-12
RFC stream Internet Engineering Task Force (IETF)
Additional resources Mailing list discussion
IESG Responsible AD Alvaro Retana
Send notices to (None)
RFC 9352

Internet Engineering Task Force (IETF)                    P. Psenak, Ed.
Request for Comments: 9352                                   C. Filsfils
Updates: 7370                                                A. Bashandy
Category: Standards Track                                  Cisco Systems
ISSN: 2070-1721                                              B. Decraene
                                                                   Z. Hu
                                                     Huawei Technologies
                                                           February 2023

  IS-IS Extensions to Support Segment Routing over the IPv6 Data Plane


   The Segment Routing (SR) architecture allows a flexible definition of
   the end-to-end path by encoding it as a sequence of topological
   elements called "segments".  It can be implemented over the MPLS or
   the IPv6 data plane.  This document describes the IS-IS extensions
   required to support SR over the IPv6 data plane.

   This document updates RFC 7370 by modifying an existing registry.

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

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
   ( 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
     1.1.  Requirements Language
   2.  SRv6 Capabilities Sub-TLV
   3.  Advertising Supported Algorithms
   4.  Advertising Maximum SRv6 SID Depths
     4.1.  Maximum Segments Left MSD Type
     4.2.  Maximum End Pop MSD Type
     4.3.  Maximum H.Encaps MSD Type
     4.4.  Maximum End D MSD Type
   5.  SRv6 SIDs and Reachability
   6.  Advertising Anycast Property
   7.  Advertising Locators and End SIDs
     7.1.  SRv6 Locator TLV Format
     7.2.  SRv6 End SID Sub-TLV
   8.  Advertising SRv6 Adjacency SIDs
     8.1.  SRv6 End.X SID Sub-TLV
     8.2.  SRv6 LAN End.X SID Sub-TLV
   9.  SRv6 SID Structure Sub-Sub-TLV
   10. Advertising Endpoint Behaviors
   11. IANA Considerations
     11.1.  SRv6 Locator TLV
       11.1.1.  SRv6 End SID Sub-TLV
       11.1.2.  IS-IS Sub-TLVs for TLVs Advertising Prefix
               Reachability Registry
     11.2.  SRv6 Capabilities Sub-TLV
     11.3.  IS-IS Sub-Sub-TLVs for the SRv6 Capabilities Sub-TLV
     11.4.  SRv6 End.X SID and SRv6 LAN End.X SID Sub-TLVs
     11.5.  MSD Types
     11.6.  IS-IS Sub-Sub-TLVs for SRv6 SID Sub-TLVs Registry
     11.7.  Prefix Attribute Flags Sub-TLV
     11.8.  IS-IS SRv6 Capabilities Sub-TLV Flags Registry
     11.9.  IS-IS SRv6 Locator TLV Flags Registry
     11.10. IS-IS SRv6 End SID Sub-TLV Flags Registry
     11.11. IS-IS SRv6 Adjacency SID Sub-TLVs Flags Registry
   12. Security Considerations
   13. References
     13.1.  Normative References
     13.2.  Informative References
   Authors' Addresses

1.  Introduction

   With Segment Routing (SR) [RFC8402], a node steers a packet through
   an ordered list of instructions, which are called segments.

   Segments are identified through Segment Identifiers (SIDs).

   SR can be directly instantiated on the IPv6 data plane through the
   use of the Segment Routing Header (SRH) defined in [RFC8754].  SRv6
   refers to this SR instantiation on the IPv6 data plane.

   The network programming paradigm [RFC8986] is central to SRv6.  It
   describes how any behavior can be bound to a SID and how any network
   program can be expressed as a combination of SIDs.

   This document specifies IS-IS extensions that allow the IS-IS
   protocol to encode some of these SIDs and their behaviors.

   Familiarity with the network programming paradigm [RFC8986] is
   necessary to understand the extensions specified in this document.

   The new SRv6 Locator top-level TLV announces SRv6 Locators -- a form
   of summary address for the set of topology-/algorithm-specific SIDs
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