Avaya Configuring IP, ARP, RARP, RIP, and OSPF Services Instrukcja Użytkownika Pobierz pdf (Strona 38)

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Configuring IP, ARP, RARP, RIP, and OSPF Services

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Designated Routers

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

designated router and a backup designated router on each multiaccess broadcast

network. Instead of neighboring routers forming adjacencies and exchanging 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 adjacencies 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. The backup designated router takes over all of the designated

router’s functions should the designated router fail.

AS External Routes

OSPF considers the following routes to be AS external (ASE) routes:

• Static route (host, network, or default)

• Route derived by RIP or BGP

• Directly connected network not running OSPF

In Figure 1-6

, for example, routers R1 and R2 are boundary routers that use BGP

to connect the backbone to external ASs. R7 in area 0.0.0.1 and R15 in area

0.0.0.3 are also boundary routers that use RIP to connect to external ASs. R19 in

area 0.0.0.4 connects the area to an external AS via BGP.

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