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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. In this case, backbone connectivity must be restored through virtual links. Virtual links are
configured between any backbone routers that share a link to a non-backbone area and function as if they
were direct links.
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.
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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 virtual link cannot traverse stubby areas.
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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. However, a virtual link can
traverse it.
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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.
Router Types
Router 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 connected to
more than one area, receiving routing from a border gateway protocol (BGP) process 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). You do not have to associate the router ID
with a valid IP address. However, to make troubleshooting easier, Dell Networking recommends that the
router ID and the router's IP address reflect each other.
Open Shortest Path First (OSPFv2 and OSPFv3)
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Table of Contents
Troubleshooting
