Merry Xmas! Outgoing traffic from the tunnel endpoint is sent to the router and looks correctly encapsulated to me, but no reply is received: # tcpdump -s0 -plni eth0 host 212.224.0.189 or icmp tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes 11:29:56.881732 IP 188.40.164.106 > 212.224.0.189: IP6 2001:6f8:1c00:12c::2 > 2001:6f8:1c00:12c::1: ICMP6, echo request, seq 1, length 64 11:29:57.881732 IP 188.40.164.106 > 212.224.0.189: IP6 2001:6f8:1c00:12c::2 > 2001:6f8:1c00:12c::1: ICMP6, echo request, seq 2, length 64 Ping to my end of the tunnel from an outside host gets ICMP unreachable replies from a router, no traffic is seen arriving on the endpoint: 11:06:56.982657 IP6 2001:6f8:13a6::1 > 2001:6f8:1c00:12c::2: ICMP6, echo request, seq 1, length 64 11:06:56.995160 IP6 2001:6f8:800:1003::3 > 2001:6f8:13a6::1: ICMP6, destination unreachable, unreachable address 2001:6f8:1c00:12c::2, length 112 11:06:57.984226 IP6 2001:6f8:13a6::1 > 2001:6f8:1c00:12c::2: ICMP6, echo request, seq 2, length 64 11:06:57.995136 IP6 2001:6f8:800:1003::3 > 2001:6f8:13a6::1: ICMP6, destination unreachable, unreachable route 2001:6f8:1c00:12c::2, length 112 11:06:58.986163 IP6 2001:6f8:13a6::1 > 2001:6f8:1c00:12c::2: ICMP6, echo request, seq 3, length 64 11:06:58.995110 IP6 2001:6f8:800:1003::3 > 2001:6f8:13a6::1: ICMP6, destination unreachable, unreachable route 2001:6f8:1c00:12c::2, length 112 This is what the endpoint config in /etc/network/interfaces (Debian) looks like: auto sixxs iface sixxs inet6 v4tunnel address 2001:6f8:1c00:12c::2 netmask 64 endpoint 212.224.0.189 ttl 64 up ip link set mtu 1280 dev sixxs up ip route add default via 2001:6f8:1c00:12c::1 dev sixxs # ip addr show dev sixxs 6: sixxs@NONE: <POINTOPOINT,NOARP,UP,LOWER_UP> mtu 1280 qdisc noqueue state UNKNOWN link/sit 0.0.0.0 peer 212.224.0.189 inet6 2001:6f8:1c00:12c::2/64 scope global valid_lft forever preferred_lft forever inet6 fe80::bc28:a46a/64 scope link valid_lft forever preferred_lft forever # ip -f inet6 route 2001:6f8:1c00:12c::/64 via :: dev sixxs metric 256 mtu 1280 advmss 1220 hoplimit 4294967295 fe80::/64 dev eth0 metric 256 mtu 1500 advmss 1440 hoplimit 4294967295 fe80::/64 via :: dev sixxs metric 256 mtu 1280 advmss 1220 hoplimit 4294967295 default via 2001:6f8:1c00:12c::1 dev sixxs metric 1024 mtu 1280 advmss 1220 hoplimit 4294967295 I have verified that the endpoint host can receive encapsulated v6 traffic from other hosts so I am confident that the endpoint's traffic is not being filtered. Please note that the tunnel was initially created as an AYIYA tunnel, and the mode was later changed to static. Maybe this screwed something up. Regards & TIA, Jan