Network dropouts on Debian 5, how to find a cause

Solution 1:

First thing to check is if any link state changes are logged in the kernel log. You can view the most recent kernel log messages using the dmesg command. Look for messages looking similar to this

eth2: link down
eth2: link up, 100Mbps, full-duplex, lpa 0xC5E1
eth2: link down
eth2: link up, 100Mbps, full-duplex, lpa 0x45E1

If you see such messages, you need to check cabling between computer and switch. If you do not see this, you should check on a slightly higher layer of the stack.

Another problem could be that the MAC or IP address is duplicated. If that's the reason for your problem, running tcpdump on the server would likely show outgoing but not incoming packets. Though it may be the case, that the first outgoing packet clears the problem.