Maybe you are suffering the problem with some types of cable router that I noticed when trying to reach another US amprnet station. Those routers claim to support a DMZ mode and you set the IPIP tunnel server as the DMZ host, but in reality they do not forward new incoming IPIP packets to the DMZ host, they only forward "replies" to outgoing IPIP tunnel packets just like they do for normal NAT traffic. So, you configure your IPIP tunnel host, you test connectivity with other systems by pinging or telnet or whatever, and all appears to be fine. However, when anyone else attempts to connect to you from the outside, your system is just unreachable. When you do a ping to one of them and they try to reach you, it works OK. But when there is no traffic for a few minutes, the gate closes again and you are unreachable. The DMZ feature probably only works for TCP and UDP. For IPIP, you are just relying on the standard NAT feature which of course is causing the problem described above. Rob