Avaya Configuring IP Services Bedienungsanleitung PDF herunterladen (Seite 144)

Configuring IP Services

4-6

Bidirectional communication is determined when one router sees itself listed in

the neighbor’s Hello packet.

Establishing Adjacencies

Neighbors may form an

adjacency

for the purpose of exchanging routing

information. When two routers form an 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 routing change information is passed between the adjacencies, thus

conserving bandwidth.

All routers connected by a point-to-point network or a virtual link will always

form an adjacency. Also, every router on a multiaccess network forms an

adjacency relationship with the designated router and the backup designated

router.

Electing a Designated and Backup Designated Router

To further reduce the amount of routing trafﬁc, the Hello protocol elects a

designated router

and a

backup designated router

on each multiaccess network.

Instead of neighboring routers forming adjacencies and swapping link-state

information with each other (which on a large network can mean a lot of routing

protocol trafﬁc), all routers on the network form an adjacency with the designated

router and the backup designated router only and send link state information to

them. The designated router then redistributes the information from each router to

every other router.

The Hello protocol always elects a backup designated router along with the

designated router. Its responsibility is to take over all of the designated router’s

functions should the designated router fail.

For instructions on using Site Manager to set the characteristics of the Hello protocol on

an OSPF interface, see the Hello Interval parameter on page 4-31, the Dead Interval

parameter on page 4-32, and the Poll Interval parameter on page 4-32.

For instructions on using Site Manager to conﬁgure a connection to a neighbor on a

nonbroadcast multiaccess network, see “Adding a Neighbor to an NBMA Interface” on

page 4-55.

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Avaya Configuring IP Services Bedienungsanleitung Seite 144