694 | Open Shortest Path First (OSPFv2 and OSPFv3)w w w . d e l l . c o m | s u p p o r t . d e l l . c o m A Stub Area (SA) does not receive external route information, except for the default route. These areas doreceive information from inter-area (IA) routes. Note that all routers within an assigned Stub area must beconfigured as stubby, and no generate LSAs that do not apply. For example, a Type 5 LSA is intended forexternal areas and the Stubby area routers may not generate external LSAs. Stubby areas cannot betraversed by a virtual link.A Not-So-Stubby Area (NSSA) can import AS external route information and send it to the Backbone. Itcannot received external AS information from the Backbone or other areas. It can be traversed by a virtuallink.Totally Stubby Areas are referred to as No Summary areas in FTOS.Networks and NeighborsAs a link-state protocol, OSPF sends routing information to other OSPF routers concerning the state of thelinks between them. The state (up or down) of those links is important.Routers that share a link become neighbors on that segment. OSPF uses the hello protocol as a neighbordiscovery and keep alive mechanism. After two routers are neighbors, they may proceed to exchange andsynchronize their databases, which creates an adjacency.Router TypesRouter types are attributes of the OSPF process. A given physical router may be a part of one or moreOSPF processes. For example, a router connected to more than one area, receiving routing from a BGPprocess connected to another AS acts as both an Area Border Router and an Autonomous System Router.Each router has a unique ID, written in decimal format (A.B.C.D). The router ID does not have to beassociated with a valid IP address. However, Force 10 recommends that the router ID and the router’s IPaddress reflect each other, to make troubleshooting easier.Figure 32-2gives some examples of the different router designations.Note: You can log adjacency state changes for OSPFv2 and v3 with the command log-adjacency-changesfrom ROUTER OSPF mode.
