Ospf; Chapter 28 Ospf; Ospf Overview; Ospf Autonomous Systems And Areas - ZyXEL Communications ZyXEL Dimension ES-4124 User Manual

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H A P T E R
This chapter describes the OSPF (Open Shortest Path First) routing protocol and shows you
how to configure OSPF.

28.1 OSPF Overview

OSPF (Open Shortest Path First) is a link-state protocol designed to distribute routing
information within an autonomous system (AS). An autonomous system is a collection of
networks using a common routing protocol to exchange routing information.
OSPF offers some advantages over traditional vector-space routing protocols (such as RIP).
The following table summarizes some of the major differences between OSPF and RIP.

Table 84 OSPF vs. RIP

Network Size
Metrics
Convergence

28.1.1 OSPF Autonomous Systems and Areas

An OSPF autonomous system can be divided into logical areas. Each area represents a group
of adjacent networks. All areas are connected to a backbone (also known as area 0). The
backbone is the transit area to route packets between two areas. A stub area, at the edge of an
AS, is not a transit area since there is only one connection to the stub area.
The following table describes the four classes of OSPF routers.

Table 85 OSPF: Router Types

TYPE
Internal Router (IR)
Area Border Router
(ABR)
Backbone Router (BR)
AS Boundary Router
ES-4124 User's Guide

OSPF

Large
Bandwidth, hop count, throughput, round
trip time and reliability.
Fast
DESCRIPTION
An Internal or intra-area router is a router in an area.
An Area Border Router connects two or more areas.
A backbone router has an interface to the backbone.
An AS boundary router exchanges routing information with routers in
other ASes.
28
OSPF
RIP
Small (with up to 15 routers)
Hop count
Slow
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