Troubleshooting Route Summarization in OSPF

This section discusses a feature in OSPF called route summarization. The idea is that if there are contiguous ranges of addresses, instead of advertising every network, you can form a group of contiguous networks and summarize those networks in one, two, or fewer blocks and advertise those blocks. This feature helps reduce the size of the routing table. Reducing the routing table size decreases the convergence time and increases OSPF performance. Thus, summarization needs to be configured manually on the router.

OSPF can use two types of summarization:

• Interarea summarization that can be done on the ABR

• External summarization that can be done on the ASBR

Two common problems related to summarization in OSPF are as follows :

• A router is not summarizing interarea routes.

• A router is not summarizing external routes.