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| 6.5 |  | Multiarea OSPF Operation |
| 6.5.2 |  | OSPF router types |

The following are four different types of OSPF routers that exist:

- Internal router – As discussed previously, routers that have all their interfaces within the same area are called internal routers. Internal routers in the same area have identical link-state databases and run a single copy of the routing algorithm.
- Backbone router – Routers that are attached to the backbone area of the OSPF network are called backbone routers. They have at least one interface connected to Area 0, the backbone area. These routers maintain OSPF routing information using the same procedures and algorithms as internal routers.
- Area Border Router (ABR) – ABRs are routers with interfaces attached to multiple areas. They maintain separate link-state databases for each area to which they are connected, and they route traffic destined to or arriving from other areas. ABRs are exit points for the area, which means that routing information destined for another area can travel there only by way of the of the local area ABR. ABRs summarize information about the attached areas from their link-state databases and distribute the information into the backbone. The backbone ABRs then forward the information to all other connected areas. An area can have one or more ABRs.
- Autonomous System Boundary Router (ASBR) – ASBRs are routers that have at least one interface connected to an external internetwork, another autonomous system, such as a non-OSPF network. These routers can import non-OSPF network information to the OSPF network, and OSPF to non-OSPF. This is referred to as redistribution.

A router can be more than one router type. For example, if a router interconnects to Area 0 and Area 1, as well as to a non-OSPF network, it would be both an ABR and an ASBR.

| Interactive Media Activity Drag and Drop: OSPF Router Types Upon completion of this activity, the student will be able to identify the four different types of OSPF routers.