OSPF Troubleshooting Tips

A Cisco Certification Exam Tutorial

By Chris Bryant, CCIE #12933

To form an OSPF adjacency, routers must agree on the hello and dead timers, stub area flag setting, and the Area ID. They do not have to agree on the process number.

The OSPF hub-and-spoke network checklist:

The hub must be the DR

The spokes must not become a DR or BDR

The hub needs neighbor statements

The spokes require ip ospf priority 0 statements

To hardcode the OSPF RID, use the router-id command under the OSPF process, then either clear the OSPF processes or reload the router.

Be careful adjusting the OSPF interface priority on a broadcast network, because if all the routers have their OSPF priority set to zero, no DR or BDR will be elected.

OSPF areas are required to contain a router that also has an interface in Area 0. A virtual link can be used to fulfill this requirement if no physical connection is possible; if Area 0 is configured for area authentication, the virtual link must be as well.

OSPF area authentication options are MD5 and clear-text. OSPF neighbors configured for authentication must agree on the options as well as the password.

If you get a message that OSPF can't start, that probably means that no interface on the router has an IP address; therefore, the OSPF process has no value to use as the OSPF RID.

To your success,

Chris Bryant

CCIE #12933

chris@thebryantadvantage.com