Configure the Backbone Area

You must create a backbone area if your network consists of multiple areas. An ABR must have at least one interface in the backbone area, or it must have a virtual link to a router in the backbone area. The backbone comprises all area border routers and all routers that are not included in any other area. You configure all these routers by including the following area statement:

[edit protocols (ospf | ospf3)]

area 0.0.0.0; 

For a list of hierarchy levels at which you can configure this statement, see the statement summary section for this statement.