Loops and oversized ethernet frames

Looks we know the origin of our problems with the VTK-server yesterday. We're not the only one having those troubles: when the sysadmin of the building connects a computer to an unused UTP-connection, the pc seems like under DoS attack. One of the network operators told about a known problem, some loop. The last message on our firewall (dmesg) indeed was "oversized ethernet frame". That could cause some delay and Metsie, the impatient one, thought our server was the problem and rebooted it with the known result. Normally it should be fixed now...