Difference Between ABR and ASBR in OSPF

OSPF is a widely used routing protocol due to its efficiency and scalability. Within OSPF, specialized routers play crucial roles in managing network paths and ensuring optimal routing. Two of these key routers are the Area Border Router (ABR) and the Autonomous System Boundary Router (ASBR).

OSPF Area Border Router (ABR) is a router that connects different OSPF areas, facilitating communication between them and the backbone area (Area 0). OSPF Autonomous System Boundary Router (ASBR) facilitates the routing of data between an OSPF network and external networks.

In this article, we have discussed the Area Border Router and Autonomous System Boundary Router in OSPF, highlighting the differences between them. Furthermore, you can check out IT infrastructure courses to learn more technical details, such as configurations.

What is OSPF Area Border Router (ABR)?

An area border router (ABR) is a router that connects one or more areas to the OSPF backbone. When a router is located near the border between one or more Open Shortest Path First (OSPF) areas.

It stores and operates different routing information related to the topology of the area to which it is attached or to the backbone, as ABR is a member of both the particular areas it is connected and the main backbone.

To make a connection between the OSPF areas and backbone networks, an ABR is used. You can define the area ID as a dotted decimal number (i.e., 0.0.0.0) or a standard number (i.e., 0).

CCNP Enterprise Live Training CourseGet CCNP Enterprise Live Training Class with Certification.Explore course

To show the path to all networks, the ABR will only send one router, i.e., the default gateway route outside the area. ABR doesn’t send full route updates to other routers, which will be time time-consuming and complex process.

Given below is an example to check whether a router is an area border router or not.

Command: show ip protocols

Ex. As it is clear from the above diagram, Router R2 is an ABR

***IP Routing is NSF aware***

The Routing Protocol is “OSPF”

The outing update filter list for all interfaces is not set

The incoming update filter list for all interfaces is not set

Router ID 2.2.2.2

It is an area border router

Number of areas in this router is 2.2 normal 0 stub 0 nssa

Maximum path: 4

Routing for Network:

12.0.0.0 0.0.0.255 area 0

23.0.0.0 0.0.0.255 area 1

Routing Information Sources:

Gateway           Distance           Last update

1.1.1.1                110                   00:01:30

Distance: (default is 110)

If you seek to achieve the certification and live CCIE Enterprise training online, then feel free to contact our learning advisors. 

Contact learner advisor

What is OSPF Autonomous System Border Router (ASBR)

Autonomous system border router (ASBR): A router that is usually connected through an exterior routing protocol like BGP to one or more logical entities (AS).

The major work of ABRs is to brief sub-networks found throughout the OSPF system. It stores many copies of its link-state database and provides the path to the router.

ASBR is a router that is attached to other OSPF areas, followed by other routing protocols like IS-IS, IGRP, BGP, EIGRP, RIP, and Static.

Given below is an example to check whether a router is an area border router or not.

Command: show ip protocols

Ex. As it is clear from the above diagram, Router R3 is an ASBR

***IP Routing is NSF aware***

Routing Protocol is “OSPF 3”

The outing update filter list for all interfaces is not set

The incoming update filter list for all interfaces is not set

Router ID 3.3.3.3

It is an autonomous system boundary router

Redistributing External Routers from,

eigrp 1, includes subnets in redistribution

Number of areas in this router is 1.1 normal 0 stub 0 nssa

Maximum path: 4

Routing for Network:

23.0.0.0 0.0.0.255 area 1

Routing Information Sources:

Gateway           Distance           Last update

2.2.2.2                110                   00:09:52

Distance: (default is 110)

Get a Better Understanding of Network Port Numbers & Protocols

Difference Between OSPF ABR and ASBR?

The ABR and ASBR comparison table below shows the key differences between Area Border Routers (ABRs) and Autonomous System Boundary Routers (ASBRs).

Conclusion

In conclusion, Area Border Routers (ABRs) is a router that connects multiple OSPF areas, including at least one backbone area (Area 0). Autonomous System Boundary Routers (ASBRs) a router that connects an OSPF network to other networks.

ABRs connect different OSPF areas, facilitating routing information exchange and generating summary LSAs to optimize inter-area communication. They also filter routes to enhance network performance.

Conversely, ASBRs connect OSPF networks to external routing domains, managing the import and export of routes between OSPF and other protocols. Understanding these roles is crucial for optimizing the OSPF network.