We have an old ISA server with public IP addresses configured for NIC "Internet" and private IP adress for NIC "LAN", and several firewall rules.
We have implemented a new TMG server with the same IP configuration as the old, and the same firewall rules. It is as far as possible identical.
We switched between them, pulling the TP cables from ISA and shoved them into the TMG.
What happened was, that both LAN and Internet NIC had the status of "Unidentified Network - No internet access", and Windows complained that there was an IP address conflict (on LAN).
I admit that our switch was a bit on the optimistic side, but nonetheless I can't figure out why it doesn't work. Has it something to do with IP address--MAC address mappings in routers and switches, and if so, surely I don't need to restart every node, TMG included?