The backbone is the only area with a default area number. All other areas can have their Area ID assignedin the configuration.In the previous example, Routers A, B, C, G, H, and I are the Backbone.• A stub area (SA) does not receive external route information, except for the default route. These areasdo receive information from inter-area (IA) routes.NOTE: Configure all routers within an assigned stub area as stubby, and not generate LSAs thatdo not apply. For example, a Type 5 LSA is intended for external areas and the Stubby arearouters may not generate external LSAs. A virtual link cannot traverse stubby areas.• A not-so-stubby area (NSSA) can import AS external route information and send it to the backbone. Itcannot receive external AS information from the backbone or other areas. However, a virtual link cantraverse it.• Totally stubby areas are referred to as no summary areas in the Dell Networking OS.Networks and NeighborsAs a link-state protocol, OSPF sends routing information to other OSPF routers concerning the state ofthe links 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 more OSPF processes. For example, a router connectedto more than one area, receiving routing from a border gateway protocol (BGP) process connected toanother 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). You do not have to associate the routerID with a valid IP address. However, to make troubleshooting easier, Dell Networking recommends thatthe router ID and the router’s IP address reflect each other.The following example shows different router designations.616 Open Shortest Path First (OSPFv2 and OSPFv3)
