OSPF (Open Shortest Path First) routers are classified into four types:
Backbone Area Router:
This is a router which resides in backbone area. The backbone area is set to area 0.
Backbone Area Router
Internal Router:
A router that has all its interfaces connected to a within same OSPF area is known as an Internal Router.
Internal Router
Area Border Router (ABR):
An ABR connects OSPF areas to each other. It acts as a bridge between the different areas, allowing the exchange of routing information.
Area Border Router
Autonomous System Boundary Router (ASBR):
An ASBR connects an OSPF network to a different routing protocol, such as BGP (Border Gateway Protocol).
The ASBR acts as a gateway between the OSPF network and the external routing domain.
ASBR