By authenticate, I mean the communications that you receive back from the ultrapeers that you connect to.

Your TCP connection to an ultrapeer reports back the IP address that it sees you as. If you connect to an ultrapeer behind some nat on a private network, it would report one IP address. If you connect to an ultrapeer through a nat, the IP address could be different. So, the question is, does SBC Yahoo have this type of configuration.

If it is common, then LimeWire needs to improve its handling of this. I've wanted better private network support for a while.