Hi all,
This isn't directly certification-related, but maybe people can practise
their trouble-shooting skills.
I have a frame relay link that occasionally drops the OSPF adjacency across
it (average once a day maybe, but it can go several days with no problems
and then get several hits in a day). Apart from the brief disruption, this
causes the ISDN backup to kick in, which is not something I want to happen
unnecessarily since the call is from one side of Australia to the other :-)
Each access supports other PVCs as well, which do not have problems.
The PVC does not drop out.
I have debug ip ospf events and debug ip ospf adjacency turned on. One
side will announce that the other neighbour is dead, and start rebuilding
the adjacency. The side that detects the problem first varies.
There are a small number of CRC errors at one end, and some broadcasts are
dropped at the other end, but the numbers are consistent with links
throughout the rest of the network which are problem-free.
Both routers have had the cables re-seated and have been reloaded.
Traffic shaping is in effect and should be preventing traffic from
overloading the smaller access rate. There are some FECN/BECN/DE packets,
but again, nothing at unusual levels. I have no reason to believe that the
traffic pattern on this link is different to others in the network.
IOS is 11.2. One router is a 7505, the other a 4700M.
I assume that hellos are being dropped occassionally (and fairly randomly)
across the link, and that sometimes enough in a row get dropped that the
timer expires. The links are monitored via MRTG, and there is some
correlation between increased usage and the problem, but there are plenty
of times of higher utilisation with no problems. Very short-term bursty
traffic may not show up in MRTG, though.
Any tips on what to check/fiddle with next? My thought is to get the
carrier to check out the link and see whether they can see any problems in
their cloud. I have no doubt the answer will be 'no', but they may fix
something while they're looking :-).
Ta,
JMcL
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