Configuring the Backbone Area and Other Areas

You can group the routers in a single autonomous system (AS) into areas to reduce the amount of link-state advertisement (LSA) traffic on the network and to reduce the size of the topological databases that OSPF routers must maintain. If you do this, the AS must contain a single backbone area and optionally can contain any number of nonbackbone areas. The routers that make up the backbone must be physically contiguous. If they are not, you must configure virtual links to create the appearance of connectivity. You also can configure stub areas, which are areas through which AS external advertisements are not flooded, and not-so-stubby areas (NSSAs), which allow external routes to be flooded within an area.

To configure areas, you can perform the following tasks:

• Configuring the Backbone Area
• Configuring a Nonbackbone Area
• Configuring a Stub Area
• Configuring a Not-So-Stubby Area
• Configuring an OSPF Virtual Link

See "Example: Configuring an OSPF Virtual Link" for a virtual link configuration example.