Quote:
I still don't get how ARP doesn't end up with it's knickers in a twist when DHCP gets involved. (release address and allocate a new one).

When a new machine comes online and when an already-online machine gains a new IP address, it is supposed to generate a gratuitous ARP request. (That is, it asks if anyone knows what MAC address its own IP address is at, then it answers it itself.) That gratuituous ARP should put the new information in the ARP table of every machine listening on the local network.

You can often see the sort of problem you're expecting when you hot swap two machines with the same IP address. The new machine may not realize that it ought to send out a gratuitous ARP (computers don't tend to do it when their network connection goes offline for a second, for example), so all the other computers, often including switches, still have the old information cached.
_________________________
Bitt Faulk