Challenge: OSPF neighbor changing state from DOWN to DOWN

Tuesday, November 17, 2009

I’ve had an interesting discussion with Nicolas who optimized my OSPF neighbor loss EEM applet assuming the OSPF-5-ADJCHG message reports only OSPF neighbor state transitions from DOWN to FULL and from FULL to DOWN. I knew I'd seen stranger messages in my lab and was able to produce these ones after fumbling with OSPF configurations of two routers connected with a serial link:

*19:34:42.765: %OSPF-5-ADJCHG: Process 1, Nbr 10.0.1.1 on Serial1/0 from →
  EXSTART to DOWN, Neighbor Down: Too many retransmissions
*19:35:42.773: %OSPF-5-ADJCHG: Process 1, Nbr 10.0.1.1 on Serial1/0 from →
  DOWN to DOWN, Neighbor Down: Ignore timer expired

The messages are repeated approximately every three minutes (using the default OSPF timers).

Here's the challenge: what was going on and how was I able to produce these messages?

Tags:

9 comments:

  2. Masood Ahamd Shah17 November, 2009 08:41

    dbd packets are being filtered/dropped for some reason such as:

    mtu mismatch.
    access-list if you block unicast OSPF between the boxes you'll get exactly the symptoms ...

    ReplyDelete

  3. Hay,

    Too many retransmissions - buggy line
    Neighbor Down: Ignore timer expired - ospf message-digest-key is configured only one side

    -jumbo

    ReplyDelete

  4. There is hidden "ignore" timer. If neighbor do something wrong its ignored for period of that timer.
    How too reproduce this: on one of two routers connected by Ethernet interfaces filter unicast (but not multicast) packets of ospf protocol in both directions - routers will periodically establish two-way adjacency, but they can't exchange their databases...

    ReplyDelete

  5. MTU mismatch prevent establishing adjacency
    sol
    1-(config)#system mtu routing "mtu_value"
    or
    2-(config-if)#ip ospf mtu ignore
    Zico

    ReplyDelete
  6. Richard C Bedwell18 March, 2011 13:58

    I don't know how you did it, but I'm trying to work an OSPF relationship between a Juniper and a Cisco Router, and I keep getting the following

    %OSPF-5-ADJCHG: Process 1, Nbr xxx.xxx.xxx.xxx on VlanXXX from EXCHANGE to DOWN, Neighbor Down: Too many retransmissions
    %OSPF-5-ADJCHG: Process 1, Nbr xxx.xxx.xxx.xxx on VlanXXX from DOWN to DOWN, Neighbor Down: Ignore timer expired

    ReplyDelete
  7. Ivan Pepelnjak18 March, 2011 16:36

    MTU mismatch ignored & oversized packet lost by one of the routers:

    http://blog.ioshints.info/2009/11/ip-ospf-mtu-ignore-is-dangerous-command.html

    ReplyDelete

  9. I get the same message even though the MTUs on both sides are the same. What more can be wrong, if the MTU missmatch is not the case???

    ReplyDelete

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Ivan Pepelnjak, CCIE#1354, is the chief technology advisor for NIL Data Communications. He has been designing and implementing large-scale data communications networks as well as teaching and writing books about advanced technologies since 1990. See his full profile, contact him or follow @ioshints on Twitter.