This afternoon I lost connectivity on one of my tunnels: The POP side of the tunnel responds to IPv4 pings but not to IPv6 pings: Backstage:~# ping -c 4 91.184.37.98 PING 91.184.37.98 (91.184.37.98) 56(84) bytes of data. 64 bytes from 91.184.37.98: icmp_seq=1 ttl=58 time=16.6 ms 64 bytes from 91.184.37.98: icmp_seq=2 ttl=58 time=21.2 ms 64 bytes from 91.184.37.98: icmp_seq=3 ttl=58 time=17.2 ms 64 bytes from 91.184.37.98: icmp_seq=4 ttl=58 time=16.6 ms --- 91.184.37.98 ping statistics --- 4 packets transmitted, 4 received, 0% packet loss, time 3032ms rtt min/avg/max/mdev = 16.645/17.968/21.259/1.923 ms Backstage:~# ping6 -c4 2a01:198:200:7ee::1 PING 2a01:198:200:7ee::1(2a01:198:200:7ee::1) 56 data bytes --- 2a01:198:200:7ee::1 ping statistics --- 4 packets transmitted, 0 received, 100% packet loss, time 3016ms In the tcpdump this looks like this (192.168.22.7 is an internal IP of the host but the NAT gateway deals with protocol 41 correctly): 23:16:59.981270 IP 192.168.22.7 > 91.184.37.98: IP6 2a01:198:200:7ee::2 > 2a01:198:200:7ee::1: ICMP6, echo request, seq 11, length 64 23:16:59.998490 IP 91.184.37.98 > 192.168.22.7: ICMP 91.184.37.98 protocol 41 port 0 unreachable, length 132 The tunnel is configured to use 6in4-heartbeat. Any help would be appreciated!