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flapping ospf neighbour state

i had a pair of 6509 as the core-switch(interconnected via 3 fiber-links and set as trunk mode), which are inter-connected to a few vlans.

Now I am facing some ospf neighbour state issue.

The ospf neighbour statse on both switches will reset after every 30 mins(approx).

And during the process of changing from down to full state, I am not able to ping each other.

any comments, or how should i go about troubleshooting?


Re: flapping ospf neighbour state

It sounds like you are having a unicast traffic issue which crops up every 30 minutes or so--if you can't ping between the routers, OSPF is the victim, most likely. You could verify this if you have ospf log-neighbor-changes on, by checking both sides to see what the reason is for the lost adjacency. If it's a unicast issue, then I would suspect you would see a restransmission timout between the two peers. If it's a general link issue (no traffic passing through the link at all), I would expect to see a dead timer expired.

One piece of information that might be useful in troubleshooting the link problem is whether just unicast traffic is impacted, or if unicast and multicast traffic are both impacted. If you can poing, the "all OSPF routers" address, and not the unicast address, then it's probably a unicast only issue, which is going to be harder to troubleshoot. If you can't ping anything, then it's a general link issue, and you need to start looking at the state of the link, etc.

If the link is up, I would examine the input and output queues, to see if things are blocking up there, and at the number of packets dropped. It's at least possible that you are seeing some sort of attack or application that overflows the router's queues occasionally (though every 30 minutes doesn't really sound like an attack).

Another thing to look at is whether you can ping through the router or not during this time. You'll have to set up static routes to at least one subnet to test this, but it might be worth it to see if the problem is the router not being able to receive traffic, or if it's just a problem with the link in general.

That's at least some places to start....