Troubleshooting IP Routing Protocols (CCIE Professional Development Series)

This section discusses the problems related with OSPF route advertisement. OSPF is a link-state protocol. When it forms neighbor relationships, it exchanges the entire link-state database with its neighbor(s). If any database information is not shared with the neighbor, the link-state characteristics of OSPF will break.

The most common reasons for OSPF to not share the database information about a specific link are as follows :

• The OSPF neighbor is not advertising routes.

• The OSPF neighbor (ABR) is not advertising the summary route.

• The OSPF neighbor is not advertising external routes.

• The OSPF neighbor is not advertising the default route.

The sections that follow address these problems, the possible causes for each, and the solutions for resolving them.