Actually, it *does* user ICMP not UDP. UDP support is one of the things I've been toying with in my spare time to see if I can pull this off (I don't know of any windows based packages that use UDP).<br><br>Interestingly, I'm using NAT as well - and it works with Ping Plotter just fine. The NAT package I'm using is "WinRoute" (<A HREF=""></A>). I'm really impressed by the capabilities of NAT.<br><br>Are you using a PC software based firewall or a hardware one? If it's software based, you may be able to configure it to work with ICMP echo requests.<br><br>Keep me informed on your progress/success! (Also, see the questions board for a post on something related to your problem).<br><br>Pete<br><br><br>