You contact the other side, and since no Gnutella client completely trusts another one (we're friendly, but not naive), the other side doesn't connect back, but simply uses the connection you provide (and tells you, which IP it sees). But as far as I know, noone will connect to you, if you fake the IP, because they should store the faked IP, so you'll only get outgoing connections.

Aside from trust, this behaviour is necessary to find your real IP, when you're behind a router or similar (NAT).

And the question is far from dumb.

Using the IP is useful when you know your external IP yourself, so you can just give the others the true IP, so they don't have to guess it.

__________________

-> put this banner into your own signature! <-
--
Erst im Spiel lebt der Mensch.
Nur ludantaj homoj vivas.
GnuFU.net - Gnutella For Users
Draketo.de - Shortstories, Poems, Music and strange Ideas.