Hi,

We have a setup which has been seeing connectivity issues between two routers connected through a 3550 switch running 12.1(20)EA1. Periodically the OSPF neighbour relationship will drop and HSRP will become active on router2, (both issues) due to router2 not seeing packets from router 1.

(We also see other connectivity issue related to this end hosts talking to router2, but I am concentrating on these two devices to keep troubleshooting simpler)

The topology is as follows:

Router2(fa0/0)---[dot1q]---(fa0/23)switch(fa0/24)--[access_port](fa0/0)Router1

The CPU on both routers remains low at the time the issue occurs and no errors are seen from show interface on either of the routers or either of the switch ports at the time the packets are lost. The only errors which are seen are on the switch using:

Swich1#sh int fa0/23 count er

Port Align-Err FCS-Err Xmit-Err Rcv-Err UnderSize

Fa0/23 0 0 0 0 358490

Port Single-Col Multi-Col Late-Col Excess-Col Carri-Sen Runts Giants

Fa0/23 0 0 0 0 0 0 0

OR:

BR-AV-SWT-1#sh controll ethe fa0/23 | inc too s

0 Too large frames 0 Invalid frames, too small

109092189 64 byte frames 73894559 Valid frames, too small

Bug ID CSCec14238, suggests that reported undersize frames may be a cosmetic issue, however that should be fixed in the code running on the switch. Also there seems to be nothing else which would cause the loss of connectivity between the two routers.

Are the undersize frames a red herring? If so it would be nice to be able to get rid of them, if not where else should be looking?

Thanks in advance,

Dave