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Advertisement of Multiple Paths in BGP
draft-ietf-idr-add-paths-09

Document type: Active Internet-Draft (idr WG)
Document stream: IETF
Last updated: 2013-10-16
Intended RFC status: Unknown
Other versions: plain text, pdf, html

IETF State: WG Document
Consensus: Unknown
Document shepherd: Susan Hares

IESG State: I-D Exists
Responsible AD: (None)
Send notices to: No addresses provided

Network Working Group                                          D. Walton
Internet Draft                                                 A. Retana
Intended Status: Standards Track                                 E. Chen
Expiration Date: April 17, 2014                            Cisco Systems
                                                              J. Scudder
                                                        Juniper Networks
                                                        October 16, 2013

                 Advertisement of Multiple Paths in BGP

                    draft-ietf-idr-add-paths-09.txt

Status of this Memo

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

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   This Internet-Draft will expire on April 17, 2014.

Copyright Notice

   Copyright (c) 2013 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
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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document. Please review these documents
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   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.

Abstract

   In this document we propose a BGP extension that allows the
   advertisement of multiple paths for the same address prefix without
   the new paths implicitly replacing any previous ones.  The essence of
   the extension is that each path is identified by a path identifier in
   addition to the address prefix.

1. Introduction

   The BGP specification [RFC4271] defines an "Update-Send Process" to
   advertise the routes chosen by the Decision Process to other BGP
   speakers.  No provisions are made to allow the advertisement of
   multiple paths for the same address prefix, or Network Layer
   Reachability Information (NLRI).  In fact, a route with the same NLRI
   as a previously advertised route implicitly replaces the previous
   advertisement.

   In this document we propose a BGP extension that allows the
   advertisement of multiple paths for the same address prefix without
   the new paths implicitly replacing any previous ones.  The essence of
   the extension is that each path is identified by a path identifier in
   addition to the address prefix.

1.1. Specification of Requirements

   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 [RFC2119].

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2. How to Identify a Path

   As defined in [RFC4271], a path refers to the information reported in
   the path attribute field of an UPDATE message.  As the procedures
   specified in [RFC4271] allow only the advertisement of one path for a
   particular address prefix, a path for an address prefix from a BGP
   peer can be keyed on the address prefix.

   In order for a BGP speaker to advertise multiple paths for the same
   address prefix, a new identifier (termed "Path Identifier" hereafter)
   needs to be introduced so that a particular path for an address
   prefix can be identified by the combination of the address prefix and
   the Path Identifier.

   The assignment of the Path Identifier for a path by a BGP speaker is
   purely a local matter.  However, the Path Identifier MUST be assigned
   in such a way that the BGP speaker is able to use the (prefix, path
   identifier) to uniquely identify a path advertised to a neighbor.  A

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