This is the sort of thing I was talking about when I mentioned negative externalities elsewhere in this thread. NAT is nice if you want to do things like that,

This is the sort of thing I was talking about when I mentioned negative externalities elsewhere in this thread. NAT is nice if you want to do things like that, but those sorts of tricks create big problems for people like me. Being behind NAT with multiple external IPs and an unknown policy for which gets used when is a nightmare scenario for P2P applications.