5.1 Creating Multiple OSPF Areas
5.1.6 Types of areas
The characteristics you assign to an area control the type of route information it can receive. The area types possible are shown in the main figure and are described as follows:
  • Standard area --- An area that operates as discussed in "Configuring OSPF in a Single Area." This area can accept link updates and route summaries.
  • Backbone area (transit area) --- When interconnecting multiple areas, the backbone area is the central entity to which all other areas connect. The backbone area is always labeled "area 0." All other areas must connect to this area in order to exchange route information. The OSPF backbone has all of the properties of a standard OSPF area.
  • Stub area --- Refers to an area that does not accept information about routes external to the autonomous system (that is, the OSPF internetwork), such as routes from non-OSPF sources. If routers need to reach networks outside the autonomous system, they will use a default route. A default route is noted as 0.0.0.0.
  • Totally stubby area --- An area that does not accept external autonomous system (AS) routes and summary routes from other areas internal to the autonomous system. Instead, if the router needs to send a packet to a network external to the area, it sends it using a default route.