1-30Configuring OSPF Route SummarizationRoute summarization: An ABR or ASBR summarizes routes with the same prefix into a single route anddistribute it to other areas.Through route summarization, routing information across areas and the size of routing tables on routerswill be reduced, improving calculation speed of routers.Assume in an area are three internal routes 19.1.1.0/24, 19.1.2.0/24, and 19.1.3.0/24. By configuringroute summarization on the ABR, the three routes are summarized into the route 19.1.0.0/16 that isadvertised into other areas.Configuring route summarization on an ABRIf contiguous network segments are available in the area, you can summarize them into a singlenetwork segment. An ABR generates Type-3 LSAs on a per network segment basis for an attachednon-backbone area.In this way, the ABR in the area distributes only the summary LSA to reduce the scale of LSDBs onrouters in other areas and the influence of topological changes.Follow these steps to configure route summarization on an ABR:To do… Use the command… RemarksEnter system view system-view —Enter OSPF viewospf [ process-id | router-idrouter-id | vpn-instanceinstance-name ] *—Enter OSPF area view area area-id —Configure ABR routesummarizationabr-summary ip-address { mask| mask-length } [ advertise |not-advertise ] [ cost cost ]RequiredThe command is available onan ABR only.Not configured by default.Configuring route summarization when redistributing routes into OSPF on an ASBRIf summarization for redistributed routes is not configured on an ASBR, it will advertise eachredistributed route in a separate ASE LSA. After a summary is configured on the ASBR, it advertisesonly the summary route in an ASE LSA instead of more specific routes, thus reducing the number ofLSAs in the LSDBs.If summarization for redistributed routes is configured on an ASBR, it will summarize redistributedType-5 LSAs that fall into the specified address range. If the ASBR is in an NSSA area, it alsosummarizes Type-7 LSAs that fall into the specified address range. If the ASBR is also the ABR, it willsummarize Type-5 LSAs translated from Type-7 LSAs.Follow these steps to configure route summarization when redistributing routes into OSPF on an ASBR:To do… Use the command… RemarksEnter system view system-view —
