BGP Link-State extensions for Segment Routing
draft-gredler-idr-bgp-ls-segment-routing-extension-02

Abstract

Segment Routing (SR) allows for a flexible definition of end-to-end paths within link-state graphs by encoding paths as sequences of topological sub-paths, called "segments".

The link-state routing protocols (IS-IS, OSPF and OSPFv3) have been extended to advertise the segments. But flooding based propagation of path segments using IGPs is limited by the perimeter of the IGP domain. For building paths which span across IGP domains (e.g. multiple ASes), the Border Gateway Protocol (BGP) is better suited as its propagation perimeter is not limited like the IGPs.

This draft defines extensions to the BGP Link-state address-family to carry path segment information via BGP.

Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119].

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at http://datatracker.ietf.org/drafts/current/.

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This Internet-Draft will expire on April 19, 2015.

Copyright Notice

Copyright (c) 2014 IETF Trust and the persons identified as the document authors. All rights reserved.

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Table of Contents

• 1. Introduction
• 2. BGP-LS Extensions for Segment Routing
• 2.1. Node Attribute TLVs
• 2.2. Link Attribute TLVs
• 2.3. Prefix Attribute TLVs
• 3. IANA Considerations
• 4. Manageability Considerations
• 4.1. Operational Considerations
• 4.1.1. Operations
• 5. TLV/Sub-TLV Code Points Summary
• 6. Security Considerations
• 7. Acknowledgements
• 8. References
• 8.1. Normative References
• 8.2. Informative References
• Authors' Addresses

1. Introduction

Segment Routing (SR) allows for a flexible definition of end-to-end paths within link-state topologies by encoding paths as sequences of topological sub-paths, called "segments". Segment routing is an amalgamation of source routing and MPLS. In Segment Routing, the ingress node prepends a sequence of instructions, called "segments", to the packet. The SR capable nodes sequentially execute the instructions on the packet to achieve packet forwarding via required topological paths as well as service paths.

The segments can be thought of, in a simple way, to represent instructions such as "go to node N using the shortest path", "follow the shortest path for prefix P", "use link/node/ERO L", etc. Each segment is identified by a 32 bit Segment Identifier (SID) (when unmodified MPLS data-plane is used, the SIDs are restricted to 20 bits). There are "global" segments that are known to all SR nodes in the local domain, and there are local segments whose semantics are known only to the nodes that originate them. The segment routing architecture is described in [I-D.filsfils-rtgwg-segment-routing] and segment routing use-cases in [I-D.filsfils-rtgwg-segment-routing-use-cases].

Segment routing is enabled in a network by advertising the segments (including the associated SIDs) to the nodes in the network. The IGP link-state routing protocols (IS-IS [I-D.previdi-isis-segment-routing-extensions], OSPFv2 [I-D.psenak-ospf-segment-routing-extensions] and OSPFv3 [I-D.psenak-ospf-segment-routing-ospfv3-extension]) have been extended to advertise the segments. Using these extensions, segment routing can be enabled within an IGP domain.

                        +------------+
                        |  Consumer  |
                        +------------+
                              ^
                              |
                              v
                    +-------------------+
                    |    BGP Speaker    |         +-----------+
                    | (Route-Reflector) |         | Consumer  |
                    +-------------------+         +-----------+
                          ^   ^   ^                       ^
                          |   |   |                       |
          +---------------+   |   +-------------------+   |
          |                   |                       |   |
          v                   v                       v   v
    +-----------+       +-----------+             +-----------+
    |    BGP    |       |    BGP    |             |    BGP    |
    |  Speaker  |       |  Speaker  |    . . .    |  Speaker  |
    +-----------+       +-----------+             +-----------+
          ^                   ^                         ^
          |                   |                         |
         IGP                 IGP                       IGP
        

   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             |             Length            | 
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  //                        Value (variable)                     //
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+