Route summarization requires a good addressing plan-an assignment of subnets and addresses that is based on the OSPF area structure and lends itself to aggregation at the OSPF area borders. This is one of the drawbacks of summarization. If the OSPF design includes many ABRs or ASBRs, suboptimal routing is possible. Instead of advertising many specific prefixes, advertise only one summary prefix. ABRs summarize type 3 LSAs, and ASBRs summarize type 5 LSAs. With route summarization, the ABRs or ASBRs consolidate multiple routes into a single advertisement. Normally, type 1 and type 2 LSAs are generated inside each area and translated into type 3 LSAs in other areas. To reduce the size of the area database, you can configure summarization on an area boundary or autonomous system boundary. Frequent LSA flooding throughout the autonomous systemĮvery time that a route disappears in one area, routers in other areas also get involved in shortest-path calculation.Route summarization helps solve two major problems: Route summarization is a key to scalability in OSPF. Configure the default route using the default-information originate command.Describe how you can use default routes and stub routing to direct traffic toward the Internet.Configure the cost of OSPF default route.Describe benefits of route summarization in OSPF.
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