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Chapter 4

OSPF Areas

We used the OSPF debugging commands to produce this output. The con-

figuration commands consisted of two simple OSPF commands:

router ospf 1

This command starts the OSPF process on RouterA.

The number 1 indicates the OSPF process ID.

network 172.16.10.5 0.0.0.0 area 0

This command adds the net-

work (link) 172.16.10.5. The wildcard mask indicates that only this single IP
address is going to be part of the link. Area 0 indicates that the interface
with the address 172.16.10.5 is assigned to Area 0.

The generic IOS syntax for the commands is router ospf process-id

and network ip-address wildcard-mask area area-id, respectively.

Point-to-Point

Since the link described by the previous output is point-to-point, no DR/
BDR election occurred; instead, each router decided which would be the
Master and which would be the Slave. Once the Master/Slave roles had been
established, DBD packets containing LSA information for each router were
exchanged.

LSA exchanges continue until the link-state databases for each router are

identical (synchronized). Once that happens, the OSPF state changes to Full.

Broadcast

Discovering the neighbors on a broadcast network is done somewhat differ-
ently. Here you will see what happens on a broadcast multi-access network:

RouterA(config-if)#router ospf 1

RouterA(config-router)#network 172.16.230.0 0.0.0.255

area 0

OSPF: Interface Ethernet0 going Up

OSPF: Tried to build Router LSA within MinLSInterval

RouterA(config-router)#

OSPF: end of Wait on interface Ethernet0

OSPF: DR/BDR election on Ethernet0

OSPF: Elect BDR 172.16.240.1

OSPF: Elect DR 172.16.240.1

OSPF: Elect BDR 0.0.0.0

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