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Not-So-Stubby Area Configuration

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To expand upon the idea of advertising summarized routes, the area area-

id range network_address network_mask

command is used to summarize

intra-area routes on an ABR. Similarly, we can summarize external routes on

an autonomous system boundary router (ASBR) with the command summary-

address network_address network_mask

. Proper use of these summarization

tools can greatly reduce the number of routes that have to be maintained by

a router, thus reducing memory and processor overhead.

RouterC will be an even more complex configuration. Not only is

RouterC part of an NSSA, it also participates in a RIP routing process. In
order to exchange its OSPF and RIP routes, RouterC must perform route
redistribution (route redistribution is the focus of Chapter 10):

RouterC(config)#router ospf 24

RouterC(config-router)#redistribute rip

where rip is the routing protocol whose routes are being injected into the
OSPF routing process.

RouterC(config-router)#network 1.0.0.0 0.255.255.255 area 1

RouterC(config-router)#default-metric 128

where 128 is the OSPF metric value to be assigned to routes being redistrib-
uted into the OSPF routing process.

RouterC(config-router)#area 1 nssa

RouterC(config-router)#router rip

This enables the RIP routing process on the router.

RouterC(config-router)#redistribute ospf 24

where ospf 24 is the routing process whose routes are being injected into the
RIP routing process.

RouterC(config-router)#network 172.16.0.0

RouterC(config-router)#default-metric 3

where 3 is the RIP metric value (hop count) to be assigned to routes being
redistributed into the RIP routing process.

RouterD is internal to the RIP routing process. Therefore, RouterD does

not require any NSSA-specific configuration:

RouterD(config)#router rip

RouterD(config-router)#network 172.16.0.0

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