OSPF Routers have different responsibilities depending on their position and functionality. Let’s look at them-
The Internal Router – This router exists within an area. It’s responsible for maintaining a current and accurate database of every subnet within an area . It’s also responsible for forwarding data to other networks by the shortest path.
The Backbone Router – This router exists within the backbone area, also called Area 0. On some routers, it’s also known as Area 0.0.0.0.
The Area Border Router – Also known as ABR, it’s responsible for connecting two or more areas. It holds a full topological database for each area to which its connected and sends LSA updates between the areas.
The Autonomous System Boundary Router – Also known as ABSR, is used to connect to a network or routing protocol outside the OSPF domain. This router should reside in the backbone area.