Advertisement of Multiple Paths in BGP
draft-ietf-idr-add-paths-07

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Network Working Group                                          D. Walton
Internet Draft                                                   E. Chen
Intended Status: Standards Track                           Cisco Systems
Expiration Date: December 18, 2012                             A. Retana
                                                     Hewlett-Packard Co.
                                                              J. Scudder
                                                        Juniper Networks
                                                           June 17, 2012

                 Advertisement of Multiple Paths in BGP

                    draft-ietf-idr-add-paths-07.txt

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
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   Copyright (c) 2012 IETF Trust and the persons identified as the
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   This document is subject to BCP 78 and the IETF Trust's Legal
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INTERNET DRAFT       draft-ietf-idr-add-paths-07.txt           June 2012

   to this document. Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
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   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
   BGP speaker that re-advertises a route MUST generate its own Path
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