New Training: OSPF Summarization and Filtering

In this 8-video skill, CBT Nuggets trainer Keith Barker teaches you how to configure and verify standard summarization and filtering in OSPF. Watch this new Cisco training.

Learn Cisco with one of these courses:

• Cisco CCNP Enterprise Core

• Cisco OSPF Configuration

This training includes:

• 8 videos

• 49 minutes of training

You’ll learn these topics in this skill:

• Intro to OSPF Filtering and Summarization

• Summarize at the ABR

• Summarize at the ASBR

• Filtering Routes at the ABR using Not-Advertise

• Filtering Routes at the ABR with a Filter-List

• Local OSPF Route Filtering

• Filtering at the ASBR

• Review, and What is Next…

What is Open Shortest Path First (OSPF) Summarization?

Open Shortest Path First (OSPF) summarization is a means to reduce the size of routing tables and route computation when using OSPF. Unlike Enhanced Interior Gateway Routing Protocol (EIGRP), OSPF doesn't have support for automatic summarization. Also, with OSPF, you cannot summarize routes within an area. This means that you can summarize routes only on area border routers (ABRs) and autonomous system boundary routers (ASBRs), as opposed to EIGRP, which lets you summarize routes on any router interface.

When summarizing routes, it is important to understand that you must have at least one subnet falling within the summary range for the summary route to be advertised. Also, the summary route will include the cost of the subnet that is lowest within the summary range. Finally, the ABR making the summary route will create a null0 interface in order to prevent loops.

To enable OSPF summarization, issue the following command: (config-router) area AREA_ID range IP_ADDRESS MASK.