RFC 3509 (rfc3509) - Page 1 of 12
Alternative Implementations of OSPF Area Border Routers
Alternative Format: Original Text Document
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