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Type Indicates area type:
Normal An area which can send or receive external route
information.
Stub An area which cannot send or receive external route
information. It relies on a single default route provided
by its Area Border Router (ABR) to access destinations
outside of the stub. A stub can be used to reduce the
amount of topology data that has to be exchanged
over the network.
NSSA A not so stubby area cannot send but can receive
external route information. The ABR imports external
routes and floods this information to all routers within
the NSSA.
An Autonomous System Boundary Router (ASBR) can import external routes and flood
this information to the entire Autonomous System.
Note:
To add a new Area ID, use the <Add> button. (The default 0.0.0.0 indicates the
OSPF backbone.) To modify or delete an existing Area ID, highlight the table
entry with the cursor and select Enter.
OSPF Area Range Configuration
After you configure an area identifier, you can specify a subnetwork address range that
covers all the individual networks in this area. This technique limits the amount of traffic
exchanged between Area Border Routers (ABRs) by allowing them to advertise a single
summary range. By summarizing routes, the routing changes within an area do not
have to be updated in the backbone ABRs or in other areas.
To optimize the route summary, first configure all the OSPF routers in an area so that
they fall within a contiguous address range. The route summary consists of an address
and mask, where the mask can be a Variable Length Subnet Mask (VLSM). Using
VLSMs allows you to configure each subnetwork within a larger network with its own
subnet mask. This provides a longer subnet mask that covers fewer host IP addresses,
thereby reducing the size of the routing tables that have to be exchanged. (For more
information on VLSMs, see RFCs 1219 and 1878.)