OSPF Router Types:

There are four types of OSPF routers. Router types are determined by a router’s function and/or location 

within an OSPF area:

Internal (IR) – all (OSPF?)* interfaces must belong to the same OSPF area.

Backbone – at least one OSPF interface must belong to area 0 (backbone area)

Area Border Router (ABR) – at least one OSPF interface must belong to area 0 (backbone area) and at least 

one OSPF interface must belong to a non-backbone (area 0) area.

Autonomous System Boundry Router – an OSPF router that performs route injection (redistribution) from 

another route source (RIP, EIGRP, IS-IS, BGP, another OSPF process, etc.).

* An area is interface specific. A router that has all of its interfaces within the same area is called an internal 

router (IR) – Cisco OSPF Design Guide 

http://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0080094e9e.shtml 

 

Verification Command:

To verify a device’s OSPF router type, use the show ip ospf command. This command will tell you if an OSPF router is an Area 

Border Router(ABR) or an Autonomous System Boundry Router(ASBR). It will not identify Internal or Backbone routers, but if 

an OSPF router is not an ABR or ASBR, then it is an Internal router. If it’s not an ABR or an ASBR and it’s in area 0, then it’s a 

Backbone router.

r2#show ip ospf

Routing Process "ospf 1" with ID 2.2.2.2

Start time: 01:16:41.316, Time elapsed: 00:08:53.116

Supports only single TOS(TOS0) routes

Supports opaque LSA

Supports Link-local Signaling (LLS)

Supports area transit capability

It is an area border router

<--- output truncated --->

r1#show ip ospf | i It is

It is an autonomous system boundary router

r2#show ip ospf | i It is

It is an area border and autonomous system boundary router

Summary:

There are four types of OSPF routers which are determined by a router’s function and/or location within an 

OSPF area:

Internal (IR) – all OSPF interfaces must belong to the same OSPF area.

Backbone – at least one OSPF interface must belong to area 0 (backbone area)

Area Border Router (ABR) – at least one OSPF interface must belong to area 0 (backbone area) and at least 

one OSPF interface must belong to a non-backbone (area 0) area.

Autonomous System Boundry Router (ASBR) – an OSPF router that performs route injection (redistribution) 

from another route source (RIP, EIGRP, IS-IS, BGP, another OSPF process, etc.). 

You can use the show ip ospf EXEC command to identify which OSPF type(s) your device is currently 

configured as.