Illustrated TCP/IP Illustrated TCP/IP
by Matthew G. Naugle
Wiley Computer Publishing, John Wiley & Sons, Inc.
ISBN: 0471196568   Pub Date: 11/01/98  

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Chapter 129
The Backbone Area

The Backbone Area

•  There must be at least one area in an OSPF network.
•  It is called the backbone area
•  Designated by area ID of 0.0.0.0.
•  Primary responsibility to propagate information between areas.
•  Has the same attributes as any other area.
•  Any network topology can make up the backbone.
•  It can be used as a real network with attachments.

One of the areas is a specialized area. It is known as the backbone area and is labeled as 0.0.0.0 or Area 0. When a domain is split into areas, the areas communicate with one another through the backbone area. This area contains those routers and networks not contained in any other area and routers that connect to multiple areas (An ABR, explained next). Its primary responsibility is to distribute routing information between areas. The backbone area contains all the properties of its area, its topology is not known by any other area, and it does not know the topology of any other area. Okay, now that we have the distribution area (if you will), what causes the information to be in the backbone area? The ABR accomplishes this.

The backbone area has all the attributes of any typical area. This includes the fact that its topology is not known to any other area attached to it. The topologies of the areas that attach to the backbone are not known to any backbone router as well. It looks like any other area except for its area number assignment 0.0.0.0.


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