The problem is exclusive to my AYIYA tunnel T10997. I use AICCU 2007.01.15-console-linux by Jeroen Massar on a Linux hostname 2.6.19-1.2895.fc6 #1 SMP Wed Jan 10 18:50:56 EST 2007 x86_64 x86_64 x86_64 GNU/Linux. The following occurs: AICCU starts up properly, the aiccu test succeeds up to step 6, step 6 fails. When I ping6 my IPv6 2001:808:e100::2 from an external IP and I tcpdump this on the 2001:808:e100::2 machine on the eth interface, I get: however, if I do a netstat I see: It seems that a connection is already established between the aiccu running on my machine and 212.126.28.49. However, the packets corresponding to my ping6ing come from 150.254.166.147, as the tcpdump shows. Because of this established connection to 212.126.28.49, all packets from 150.254.166.147 are refused. I did a little debugging, and the aiccu listening thread indeed just hangs there on the recvfrom() in common/ayiya.c, receiving nothing from srv1.almainternet.pl. But there is a little bit of confusion about 212.126.28.49: Here is the traffic for 212.126.28.49 after restarting aiccu: NOTE: this tcpdump is from another session, that is why packets originate from 192.168.0.5.32771 and not from 192.168.0.5.33076 as above. The corresponding netstat is: Nothing is received from 212.126.28.49. Please help, my AYIYA tunnel does not work because it refuses all the packets from 150.254.166.147! (I had both iptables and ip6tables down, of course, when doing this analysis.)