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Configuring IP Services

4-22

All routers in an OSPF area must have databases that are synchronized for that

area. First, the routers in the area use the Hello protocol to discover their

neighbors — each router sends periodic hello packets out all interfaces and checks

to see itself listed in the hello packets it receives from other routers. Next, it forms

an adjacency relationship with certain neighbors or, on a multiaccess network,

with the designated router and backup designated router. This relationship is

established to facilitate the distribution of routing information. All routing

protocol packets, except for the hello packet, are sent over adjacencies.

By issuing link state advertisements, adjacent routers synchronize their area

topology databases to facilitate routing between sources and destinations within

the area. To route beyond the area, a router depends on area border routers. These

border routers advertise topology information to the backbone; the backbone, in

turn, advertises the information to all other areas, thus facilitating routing between

different areas. Each AS boundary router exchanges information with routers from

other autonomous systems or with routers from RIP networks within the same

autonomous system. Each AS boundary router receives routes from external

networks — for example, RIP or EGP networks — which it advertises throughout

the autonomous system. Each router in the area knows the path to every boundary

router, thus facilitating routing to external networks.

For More Information about OSPF

If you would like more information about OSPF, refer to the following

documents:

Moy, J. “OSPF Version 2.” RFC 1247, Network Information Center (NIC), SRI

International, Menlo Park, California, July 1991.

Comer

Douglas E.

Internetworking with TCP/IP, Volume I: Principle, Protocols,

and Architecture

. 2d ed. Englewood Cliffs, N.J., Prentice Hall, Inc., 1991.

Perlman

Radia

. Interconnections: Bridges and Routers.

Reading, Massachusetts:

Addison-Wesley Publishing Company, 1992.

OSPF Implementation Notes

This section provides some suggestions to help you conﬁgure your OSPF

network. The Bay Networks OSPF implementation does not restrict you to these

suggestions, but we are providing them as guidelines.

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Avaya Configuring IP Services Manual do Utilizador Página 160