Browse Prior Art Database

Alternative Implementations of OSPF Area Border Routers (RFC3509)

IP.com Disclosure Number: IPCOM000012090D
Original Publication Date: 2003-Apr-01
Included in the Prior Art Database: 2003-Apr-08
Document File: 13 page(s) / 24K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

A. Zinin: AUTHOR [+3]

Abstract

Open Shortest Path First (OSPF) is a link-state intra-domain routing protocol used for routing in IP networks. Though the definition of the Area Border Router (ABR) in the OSPF specification does not require a router with multiple attached areas to have a backbone connection, it is actually necessary to provide successful routing to the inter-area and external destinations. If this requirement is not met, all traffic destined for the areas not connected to such an ABR or out of the OSPF domain, is dropped. This document describes alternative ABR behaviors implemented in Cisco and IBM routers.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 11% of the total text.

Network Working Group� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � A. Zinin

Request for Comments: 3509� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � Alcatel

Category: Informational� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � A. Lindem

� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � Redback Networks

� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � D. Yeung

� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � Procket Networks

� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � April 2003

� � � � � � � Alternative Implementations of OSPF Area Border Routers

Status of this Memo

� � This memo provides information for the Internet community.� It does

� � not specify an Internet standard of any kind.� Distribution of this

� � memo is unlimited.

Copyright Notice

� � Copyright (C) The Internet Society (2003).� All Rights Reserved.

Abstract

� � Open Shortest Path First (OSPF) is a link-state intra-domain routing

� � protocol used for routing in IP networks.� Though the definition of

� � the Area Border Router (ABR) in the OSPF specification does not

� � require a router with multiple attached areas to have a backbone

� � connection, it is actually necessary to provide successful routing to

� � the inter-area and external destinations.� If this requirement is not

� � met, all traffic destined for the areas not connected to such an ABR

� � or out of the OSPF domain, is dropped.� This document describes

� � alternative ABR behaviors implemented in Cisco and IBM routers.

1 Overview

1.1 Introduction

� � An OSPF routing domain can be split into several subdomains, called

� � areas, which limit the scope of LSA flooding.� According to [Ref1] a

� � router having attachments to multiple areas is called an "area border

� � router" (ABR).� The primary function of an ABR is to provide its

� � attached areas with Type-3 and Type-4 LSAs, which are used for

� � describing routes and AS boundary routers (ASBRs) in other areas, as

� � well as to perform actual inter-area routing.

Zinin, et al.� � � � � � � � � � � � � � � Informational� � � � � � � � � � � � � � � � � � � � � [Page 1]

RFC 3509� � � � � � � � � � � � � � � � � � OSPF ABR Behavior� � � � � � � � � � � � � � � � � April 2003

1.2 Motivation

� � In OSPF domains the area topology is restricted so that there must be

� � a backbone area (area 0) and all other areas must have either

� � physical or virtual connections to the backbone.� The reason for this

� � star-like topology is that OSPF inter-area routing uses the

� � distance-vector approach and a strict area hierarchy permits

� � avoidance of the "counting to infinity" problem.� OSPF prevents

� �...