Avaya Configuring IP, ARP, RARP, RIP, and OSPF Services Manuel d'utilisateur télécharger pdf (Page 37)

IP Concepts, Terminology, and Features

308627-14.20 Rev 00

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OSPF Neighbors

OSPF neighbors are any two routers that have an interface to the same network. In

each OSPF network, routers use the Hello protocol to discover their neighbors and

maintain neighbor relationships called adjacencies. On a broadcast or

point-to-point network, the Hello protocol dynamically discovers neighbors;

however, on a nonbroadcast multi-access network, you must manually configure

neighbors.

The Hello protocol ensures that communication between neighbors is

bidirectional. Periodically, OSPF routers send out Hello packets over all

interfaces. Included in these Hello packets is the following information:

• The router’s priority

• The router’s Hello timer and dead timer values

• A list of routers that have sent Hello packets to this router on this interface

• The router’s choice for designated router and backup designated router

Bidirectional communication is verified when one router sees itself listed in the

neighbor’s Hello packet.

Neighbor Adjacencies

Neighbors can form an adjacency for exchanging link state information. When

two routers form a full adjacency, they go through a process called database

exchange to synchronize their topological databases. When their databases are

synchronized, the routers are said to be fully adjacent. From this point on, only

link state information is passed between the routers, thus conserving bandwidth.

Routers connected by a point-to-point network always form an adjacency. Also,

every router on a multiaccess network forms an adjacency relationship with the

designated router and the backup designated router.

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Avaya Configuring IP, ARP, RARP, RIP, and OSPF Services Manuel d'utilisateur Page 37