A so called 'Host cache' will provide you with a fresh list of IPs/port of other gnutella clients, every time queried. Does this answer your question, do you need technical details? Here is a list of hostcaches I have knowledge of:

"Gnutella Host Caches"
http://www.gnutella.co.uk/servers/

connect1.gnutellanet.com:6346
connect2.gnutellanet.com:6346
connect3.gnutellanet.com:6346
connect4.gnutellanet.com:6346
gnutella.hostscache.com:6346
gnotella.fileflash.com:6346
router.limewire.com:6346
gnutella.hostscache.com:6346
gnet2.ath.cx:6346

Greets, Moak