Configuring OSPF Special Area Types参考.ppt

Configuring OSPF Configuring OSPF Special Area Types Types of Areas Stub and Totally Stub Area Rules An area can be stub or totally stub if: There is a single ABR, or if there is more than one ABR, suboptimal routing paths to other areas or external autonomous systems are acceptable. All routers in the area are configured as stub routers. There is no ASBR in the area. The area is not area 0. No virtual links go through the area. Using Stub Areas Stub Area Configuration OSPF Stub Area Configuration Example Using Totally Stubby Areas Totally Stubby Configuration Totally Stubby Configuration Example Routing Table in a Standard Area Routing Table in a Stub Area Routing Table in a Stub Area with Summarization Routing Table in a Totally Stubby Area Not-So-Stubby Areas NSSA Configuration Example: NSSA Configuration NSSA Totally Stubby Configuration show Commands for Stub and NSSA Summary There are several OSPF area types: standard, backbone, stub, totally stubby, and NSSA. Use the area area-id stub command to define an area as stubby. Use the area area-id stub command with the no-summary keyword on the ABR only to define an area as totally stubby. For stub areas, external routes are not visible in the routing table, but are accessible via the intra-area default route. For totally stubby areas, interarea and external routes are not visible in the routing table, but are accessible via the intra-area default route. Use the area area-id nssa command to define an area as NSSA. Use show ip ospf, show ip ospf database, show ip route commands to verify all types of stub areas. Use the show ip ospf database nssa-external command to display details of type 7 LSAs. Configuring OSPF OSPF Route Summarization Benefits of Route Summarization Minimizes number of routing table entries Localizes impact of a topology change Reduces LSA type 3 and 5 flooding and saves CPU resources Using Route Summarization Interarea summary link carries mask. One or more entries can represent several subnet