Definition
Autonomous System Boundary Router
An autonomous system boundary router (ASBR) is a router that connects an OSPF network to other external networks, including networks outside the OSPF domain or other Autonomous Systems. The ASBR is responsible for importing routing information from external sources into the OSPF domain and potentially redistributing OSPF routes to external networks.
It connects different systems with possibly different routing protocols.
Functions
Import of External Routes
The ASBR imports routes from external sources, such as static routes, routes from different routing protocols (e.g., BGP, EIGRP, RIP), or directly connected networks that are not part of the OSPF domain. These routes are then advertised to the OSPF network as External LSAs (Link-State Advertisements).
Redistributing Routes
It redistributes OSPF routes into external routing domains, making OSPF routes known to other routing protocols and networks.