This was sent to info@sixxs.net, but I post it here as general information; maybe it helps someone else too. I have succesfully operated a heartbeat tunnel to the nlams04 POP (Scarlet) from behind a NAT (Draytek Vigor 2200E, firmware 2.3.8 (latest)) under both Linux and WinXP without any trouble whatsoever: I can ping6 hosts, hosts can ping6 me and my SSH server is accessible from the outside over IPv6. This works great, thank you SixXS! I had primarily intended this tunnel to be for usage on my non-24/7 WinXP host. Now, after 1 week, I'm trying to get a second (static) tunnel working on a (24/7) linux host to the nlams05 POP (SurfNet), and I find that I can ping6 back and forth without problems, but not transfer any other kind of traffic; I tested with tcpdump on the sixxs tunnel device: SSH to the outside: only shows outgoing packets. SSH from the outside: nada, zero, zilch, zippo. No packets. This leaves me to believe that packets can go out, but not in, and that the problem is in the NAT box; I tried both with and without using the DMZ feature, but this doesn't seem to make any difference. I even tried this method: - set up the dynamic tunnel using AICCU - stop AICCU - verify that I still have a fully functional IPv6 connection - change the local ip6 address and remote ip4 endpoint of the sixxs tunnel, and the default route to match the static tunnel parameters ...but I still end up in the aforementioned situation: ping6 works, nothing else. I'm realizing now that a ping6 packet is probably not proto-41 but ICMP, and that's why it is getting through, right? I've already sent mail to SixXS to make the second tunnel a heartbeat tunnel to solve my problems.