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.

This document defines 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.

The availability of the additional paths can help reduce or eliminate persistent route oscillations [RFC3345]. It can also help with optimal routing and routing convergence in a network by providing potential alternate or backup paths, respectively.

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].