Segment Routing Prefix Segment Identifier Extensions for BGP
RFC 8669

Document Type RFC - Proposed Standard (December 2019; No errata)
Last updated 2019-12-06
Replaces draft-keyupate-idr-bgp-prefix-sid
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IESG IESG state RFC 8669 (Proposed Standard)
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Internet Engineering Task Force (IETF)                        S. Previdi
Request for Comments: 8669                           Huawei Technologies
Category: Standards Track                                    C. Filsfils
ISSN: 2070-1721                                           A. Lindem, Ed.
                                                           Cisco Systems
                                                          A. Sreekantiah
                                                                        
                                                              H. Gredler
                                                            RtBrick Inc.
                                                           December 2019

      Segment Routing Prefix Segment Identifier Extensions for BGP

Abstract

   Segment Routing (SR) leverages the source-routing paradigm.  A node
   steers a packet through an ordered list of instructions called
   "segments".  A segment can represent any instruction, topological or
   service based.  The ingress node prepends an SR header to a packet
   containing a set of segment identifiers (SIDs).  Each SID represents
   a topological or service-based instruction.  Per-flow state is
   maintained only on the ingress node of the SR domain.  An "SR domain"
   is defined as a single administrative domain for global SID
   assignment.

   This document defines an optional, transitive BGP attribute for
   announcing information about BGP Prefix Segment Identifiers (BGP
   Prefix-SIDs) and the specification for SR-MPLS SIDs.

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/rfc8669.

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.  MPLS BGP Prefix-SID
   3.  BGP Prefix-SID Attribute
     3.1.  Label-Index TLV
     3.2.  Originator SRGB TLV
   4.  Receiving BGP Prefix-SID Attribute
     4.1.  MPLS Data Plane: Labeled Unicast
   5.  Advertising BGP Prefix-SID Attribute
     5.1.  MPLS Data Plane: Labeled Unicast
   6.  Error Handling of BGP Prefix-SID Attribute
   7.  IANA Considerations
   8.  Manageability Considerations
   9.  Security Considerations
   10. References
     10.1.  Normative References
     10.2.  Informative References
   Acknowledgements
   Contributors
   Authors' Addresses

1.  Introduction

   The Segment Routing (SR) architecture leverages the source-routing
   paradigm.  A segment represents either a topological instruction,
   such as "go to prefix P following shortest path", or a service
   instruction.  Other types of segments may be defined in the future.

   A segment is identified through a Segment Identifier (SID).  An "SR
   domain" is defined as a single administrative domain for global SID
   assignment.  It may be comprised of a single Autonomous System (AS)
   or multiple ASes under consolidated global SID administration.
   Typically, the ingress node of the SR domain prepends an SR header
   containing SIDs to an incoming packet.

   As described in [RFC8402], when SR is applied to the MPLS data plane
   ([RFC8660]), the SID consists of a label.

   [RFC8402] also describes how Segment Routing can be applied to an
   IPv6 data plane (SRv6) using an IPv6 routing header containing a
   stack of SR SIDs encoded as IPv6 addresses [IPv6-SRH].  The
   applicability and support for Segment Routing over IPv6 is beyond the
   scope of this document.

   A BGP Prefix Segment is a BGP prefix with a Prefix-SID attached.  A
   BGP Prefix-SID is always a global SID ([RFC8402]) within the SR
   domain and identifies an instruction to forward the packet over the
   Equal-Cost Multipath (ECMP) best path computed by BGP to the related
   prefix.  The BGP Prefix-SID is the identifier of the BGP Prefix
   Segment.  In this document, we always refer to the BGP Prefix Segment
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