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How to resolve common OSPF issues


Core Issue:

These are among the issues:


    Troubleshooting OSPF Neighbor States

    Troubleshooting the OSPF Routing Table

    Troubleshooting OSPF Init State

    Troubleshooting OSPF MTU

    Troubleshooting OSPF Corrupt Packets

    Troubleshooting OSPF Two-Way State

    Troubleshooting OSPF Links

    Troubleshooting Full Adjacency

    Troubleshooting External Link-State Advertisements

    Troubleshooting OSPF NBMA Networks

    Troubleshooting Access Lists

    Troubleshooting Neighbors over PRI

    Troubleshooting Ping

    Troubleshooting the OSPF Interface

    Troubleshooting Frame Relay Environment

    Troubleshooting External Route Problems

    Troubleshooting Network Type

    Troubleshooting OSPF Area Type

    Troubleshooting the Hello/Dead Interval


To resolve these issues, refer to Troubleshooting OSPF.


A) When examining an router's configuration, check the following:


    1) All interfaces have the correct addresses and masks?


    2) The configure network area statements have the correct inverse masks to match the correct interfaces?


    3) The configure network area statements put all interfaces into the correct areas?


B) When examining neighborship, consider the following questions:


    1) Are Hellos being sent from both neighbors?


    2) Are the timers(Dead and Hello) set the same between neighbors?


    3) Are the interfaces configured on the same subnet?


    4) Are the neighboring interfaces of the same network type (Broadcast, Point to point,Point to multi-point)


    5) Is a router attempting to form an adjacency with a neighbor's secondary address?


    6) If authentication is being used, is the authentication type the same between neighbors? Are the passwords same?


    7) Are any access lists blocking OSPF?


    8) If the adjacency is across a virtual link, is the link configured within a stub area?


    9) Is unique Router Id configured in the your As?


    10) Is MTU size same on the interface?


C) If a neighbor or adjacency is seeing unstable, you can monitor adjacencies using the command "debug ip ospf adj"


D)The state changes of a neighbor can be monitored by adding the command "log-adjacency-changes [detail]" under a router's OSPF configuration.


E) OSPF Errors, Warnings, and Log Messages


Receiving "ospf unknown protocol" error message


Receiving "Mismatch Authentication type"


Receiving "%ospf-4-NONEIGHBOR" error message


Receiving "ospf-5-ADJCHG"  error message


Receiving "OSPF: Hello from x.x.x.x with mismatched NSSA option bit"


F) If you suspect that a link-state database is corrupted or that two databases are not synchronized, you can use the "show ip ospf database database-summary" command to observe the number of LSAs in each router's database.

Also See:

OSPF Design Guide