An OSPF area consists of routers configured with the same area ID. To include a router in a specific area, the common area ID must be assigned and an interface identified.
If your network consists of multiple areas you must also configure a backbone area (0.0.0.0) on at least one router. The backbone consists of the area border routers and other routers not included in other areas. The backbone distributes routing information between areas. The backbone is considered to be a participating area within the autonomous system. To maintain backbone connectivity, there must be at least one interface in the backbone area or have a virtual link configured to another router in the backbone area.
The minimal configuration must include an area ID and an interface. Modifying other command parameters are optional.
Use the following syntax to configure an OSPF area.
ospf ospf-instance
area area-id
area-range ip-prefix/mask [advertise|not-advertise]
blackhole-aggregate
A:ALA-A>config>router>ospf# info
----------------------------------------------
area 0.0.0.0
exit
area 0.0.0.20
exit
----------------------------------------------
ALA-A>config>router>ospf#A: