API Guide

Figure 100. Autonomous System Areas
Area Types
The backbone of the network is Area 0. It is also called Area 0.0.0.0 and is the core of any AS.
All other areas must connect to Area 0. Areas can be defined in such a way that the backbone is not contiguous.
An OSPF backbone is responsible for distributing routing information between areas. It consists of all area border routers, networks not
wholly contained in any area, and their attached routers.
The backbone is the only area with a default area number. All other areas can have their Area ID assigned in 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 areas do receive information from
inter-area (IA) routes.
NOTE:
Configure all routers within an assigned stub area as stubby, and not generate LSAs that do not apply. For
example, a Type 5 LSA is intended for external areas and the Stubby area routers may not generate external LSAs.
• A not-so-stubby area (NSSA) can import AS external route information and send it to the backbone. It cannot receive external AS
information from the backbone or other areas.
• Totally stubby areas are referred to as no summary areas in the Dell Networking OS.
Networks and Neighbors
As a link-state protocol, OSPF sends routing information to other OSPF routers concerning the state of the 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 neighbor discovery and keep alive
mechanism. After two routers are neighbors, they may proceed to exchange and synchronize their databases, which creates an
adjacency.
Open Shortest Path First (OSPFv2 and OSPFv3)
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