ABR vs ASBR in OSPF. If you are new to Network Engineering and you are learning Dynamic Routing Protocol from scratch, you want to understand the differences between ABR vs ASBR and if there are similarities you would like to learn those too. In this post, we will learn both similarities and differences. Let's first understand both of these terms. ABR is purely an OSPF terminology, but ASBR is not. In fact, the detailed post about ASBR and the usage of ASBR in Different Places of Networking is explained in our What is ASBR Blog post. ABR - Area Border Router is a device which is connecting two different OSPF Areas. One of those OSPF areas has to be Area 0, which is also known as Backbone Area.
In the above topology, R3 is an ABR, connecting Area 0 and Area 1, R4 is an ABR as well, connecting Area 0 and Area 2. R1 is referred to as Internal Backbone Roter as it doesn't have any other connection than Area 0, Backbone Area. In this topology, there is also an ASBR - Autonomous System Boundary Router. It is called ASBR because on that router external prefixes are injected into the Internal network.
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