IPv6 Segment Routing Header (SRH)
RFC 8754

Document Type RFC - Proposed Standard (March 2020; No errata)
Last updated 2020-03-14
Replaces draft-previdi-6man-segment-routing-header
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Stream WG state Submitted to IESG for Publication
Document shepherd Bob Hinden
Shepherd write-up Show (last changed 2019-06-18)
IESG IESG state RFC 8754 (Proposed Standard)
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Send notices to Robert Hinden <bob.hinden@gmail.com>
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Internet Engineering Task Force (IETF)                  C. Filsfils, Ed.
Request for Comments: 8754                                 D. Dukes, Ed.
Category: Standards Track                            Cisco Systems, Inc.
ISSN: 2070-1721                                               S. Previdi
                                                                  Huawei
                                                                J. Leddy
                                                              Individual
                                                           S. Matsushima
                                                                SoftBank
                                                                D. Voyer
                                                             Bell Canada
                                                              March 2020

                   IPv6 Segment Routing Header (SRH)

Abstract

   Segment Routing can be applied to the IPv6 data plane using a new
   type of Routing Extension Header called the Segment Routing Header
   (SRH).  This document describes the SRH and how it is used by nodes
   that are Segment Routing (SR) capable.

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/rfc8754.

Copyright Notice

   Copyright (c) 2020 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
     1.1.  Terminology
     1.2.  Requirements Language
   2.  Segment Routing Header
     2.1.  SRH TLVs
       2.1.1.  Padding TLVs
       2.1.2.  HMAC TLV
   3.  SR Nodes
     3.1.  SR Source Node
     3.2.  Transit Node
     3.3.  SR Segment Endpoint Node
   4.  Packet Processing
     4.1.  SR Source Node
       4.1.1.  Reduced SRH
     4.2.  Transit Node
     4.3.  SR Segment Endpoint Node
       4.3.1.  FIB Entry Is a Locally Instantiated SRv6 SID
       4.3.2.  FIB Entry Is a Local Interface
       4.3.3.  FIB Entry Is a Nonlocal Route
       4.3.4.  FIB Entry Is a No Match
   5.  Intra-SR-Domain Deployment Model
     5.1.  Securing the SR Domain
     5.2.  SR Domain as a Single System with Delegation among
           Components
     5.3.  MTU Considerations
     5.4.  ICMP Error Processing
     5.5.  Load Balancing and ECMP
     5.6.  Other Deployments
   6.  Illustrations
     6.1.  Abstract Representation of an SRH
     6.2.  Example Topology
     6.3.  SR Source Node
       6.3.1.  Intra-SR-Domain Packet
       6.3.2.  Inter-SR-Domain Packet -- Transit
       6.3.3.  Inter-SR-Domain Packet -- Internal to External
     6.4.  Transit Node
     6.5.  SR Segment Endpoint Node
     6.6.  Delegation of Function with HMAC Verification
       6.6.1.  SID List Verification
   7.  Security Considerations
     7.1.  SR Attacks
     7.2.  Service Theft
     7.3.  Topology Disclosure
     7.4.  ICMP Generation
     7.5.  Applicability of AH
   8.  IANA Considerations
     8.1.  Segment Routing Header Flags Registry
     8.2.  Segment Routing Header TLVs Registry
   9.  References
     9.1.  Normative References
     9.2.  Informative References
   Acknowledgements
   Contributors
   Authors' Addresses

1.  Introduction

   Segment Routing (SR) can be applied to the IPv6 data plane using a
   new type of routing header called the Segment Routing Header (SRH).
   This document describes the SRH and how it is used by nodes that are
   SR capable.

   "Segment Routing Architecture" [RFC8402] describes Segment Routing
   and its instantiation in two data planes: MPLS and IPv6.

   The encoding of IPv6 segments in the SRH is defined in this document.

1.1.  Terminology

   This document uses the terms Segment Routing (SR), SR domain, SR over
   IPv6 (SRv6), Segment Identifier (SID), SRv6 SID, Active Segment, and
   SR Policy as defined in [RFC8402].

1.2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
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