Cabletron Systems HSIM-W6 Guia de Instalação descarregar pdf (Página 20)

Chapter 2: About the HSIM-W84

2-8 HSIM-W84 Installation Guide

IP-OSPF Hierarchy

IP-OSPF operates within a hierarchy of entities:

Autonomous System

An Autonomous System (AS) is a set of routers and networks under a common administration.

Routers inside an AS are called “interior gateways” and the protocol is called Interior Gateway

Protocol (IGP). OSPF is an IGP.

Every OSPF routing domain must have a backbone. An OSPF backbone distributes routing

information between areas in an OSPF routing domain. The backbone of an OSPF routing domain

system is an OSPF area possessing an area id of 0.0.0.0.

Areas

Areas are groups of networks and attached hosts. A router’s topology database includes area links,

and summarized and external links depicting the autonomous system topology. From this

database, routers calculate a route using the shortest-path tree algorithm.

The Hello Protocol

The Hello Protocol establishes and maintains neighbor relationships, and ensures bidirectional

communications among neighboring routers. Hello packets are sent out all router ports

periodically. A designated router is chosen by the Hello Protocol on multi-access networks and

controls adjacencies formed over the network.

Neighbors and Adjacency

The OSPF routing protocol establishes adjacencies among neighboring routers which facilitate the

exchange of routing information. Neighboring routers have interfaces to a common network and

are discovered by OSPF’s Hello Protocol.

Area Border Router

Area Border Routers (ABR) connect networks together. These routers have multiple interfaces and

participate in multiple areas. There must be at least one area border router in each area connecting

that area to a backbone. An ABR maintains a separate link-state database per area to which it is

attached.

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Cabletron Systems HSIM-W6 Guia de Instalação Página 20