Configuring OSPF Summarization During Redistribution

Unlike EIGRP, OSPF maintains a separate process for summarizing redistributed routes. This is called external route summarization. Consider the scenario depicted in Figure 3-16.

Fig u re 3-16 OSPE External Route Sutnmarization

Fig u re 3-16 OSPE External Route Sutnmarization

Router A redistributes RIP into OSPF. Normally, the redistribution injects 16 routes, each with a /24 mask, into area 0. Instead of doing that. Router A can summarize the 16 routes and inject just a single route 172.20.16.0/20 into area 0. The follow ing is Router A's OSPF configuration:

router ospf 25 network 172.20.0.0 0.0.3.255 area 0 summary-address 172.20.16.0 255.255.240.0

where summary-address 172.20.16.0 255.255.240.0 is the key command that summarizes all 16 RIP routes into a single route 172.20.16.0/20. Router A then advertises this summary route to area 0 so that the other OSPF backbone routers learn die route to the RIP destinations.

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