Open Shortest Path First - OSPF Router Types

OSPF Router Types

OSPF defines the following router types:

• Area border router (ABR)
• Autonomous system boundary router (ASBR)
• Internal router (IR)
• Backbone router (BR)

The router type is an attribute of an OSPF process. A given physical router may have one or more OSPF processes. For example, a router that is connected to more than one area, and which receives routes from a BGP process connected to another AS, is both an area border router and an autonomous system boundary router.

Each router has an identifier, customarily written in the dotted decimal format (e.g., 1.2.3.4) of an IP address. This identifier must be established in every OSPF instance. If not explicitly configured, the highest logical IP address will be duplicated as the router identifier. However, since the router identifier is not an IP address, it does not have to be a part of any routable subnet in the network, and often isn't to avoid confusion.

These router types should not be confused with the terms designated router (DR), or backup designated router (BDR), which are attributes of a router interface, not the router itself.