In fact, you want p2p content to come in from the 'net because it only transits BT's wires once...
I can't think of an obvious way for a p2p client to detect this.
What, you want to guarantee it's not coming from the local net? Easy, prefer IP addresses that aren't allocated to the same RIR that your own IP is. Network engineers at global carriers can now go ripping their hair out in frustration at the idea of all P2P traffic moving to a non-localized model ;-) ... JG -- Joe Greco - sol.net Network Services - Milwaukee, WI - http://www.sol.net "We call it the 'one bite at the apple' rule. Give me one chance [and] then I won't contact you again." - Direct Marketing Ass'n position on e-mail spam(CNN) With 24 million small businesses in the US alone, that's way too many apples.