IP Routing

Troubleshooting OSPF

OSPF is a complex organism and hence can be difficult to troubleshoot. However, since the operation of OSPF has been described in great detail by the standards bodies, the network engineer would do well to become familiar with its internal workings. The following sections describe some of the more common OSPF troubles.

OSPF Area IDs

When you’re using multiple network area statements under the OSPF configuration, the order of the statements is critical. Check that the networks have been assigned the desired area IDs by checking the output of the show ip ospf interface command.

OSPF Does Not Start

The OSPF process cannot start on a router if a router ID cannot be established. Check the output of show ip ospf to see if a router ID has been established. If a router ID has not been established, check to see if the router has an active interface (preferably a loopback interface) with an IP address.

Verifying Neighbor Relationships

Once a router has been able to start OSPF, it will establish an interface data structure for each interface configured to run OSPF. Check the output of show ip ospf interface to ensure that OSPF is active on the intended interfaces. If OSPF is active, check for the parameters described in the section Section 6.4. Many OSPF problems may be traced to an incorrectly configured interface.

   NewYork#sh ip ospf interface
   ...
   Ethernet0 is up, line protocol is up 
57   Internet Address 172.16.1.1/24, Area 0 
58   Process ID 10, Router ID 172.16.251.1, Network ...