Made the following setup: /etc/network/interfaces auto sixxs iface sixxs inet6 v4tunnel address 2001:6f8:900:99d::2 netmask 64 endpoint 212.224.0.188 ttl 64 up ip link set mtu 1280 dev sixxs up ip route add default via 2001:6f8:900:99d::1 dev sixxs Brought the device up using ifup sixxs - which works without any problems: sixxs Link encap:IPv6-in-IPv4 inet6 addr: 2001:6f8:900:99d::2/64 Scope:Global inet6 addr: fe80::4e2f:b042/64 Scope:Link inet6 addr: fe80::58c6:1794/64 Scope:Link inet6 addr: fe80::4e2f:b045/64 Scope:Link inet6 addr: fe80::4e2f:b046/64 Scope:Link UP POINTOPOINT RUNNING NOARP MTU:1280 Metric:1 RX packets:304 errors:0 dropped:0 overruns:0 frame:0 TX packets:518 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:24620 (24.0 KiB) TX bytes:57896 (56.5 KiB) But pinging/tracerouting the address of a friends tunnel (who uses the same PoP deham01) fails. I also fail pinging the PoPs IPv6 endpoint. Weird thing is, that tcpdump shows that the PoP is pinging me and the device sends the reply correctly - same happens if my friend is pinging my endpoint, but the reply never reaches him: 18:08:13.478342 IP6 2001:6f8:900:99d::1 > 2001:6f8:900:99d::2: ICMP6, echo request, seq 6, length 64 0x0000: 6000 0000 0040 3a40 2001 06f8 0900 099d `....@:@........ 0x0010: 0000 0000 0000 0001 2001 06f8 0900 099d ................ 0x0020: 0000 0000 0000 0002 8000 4cb8 0435 0006 ..........L..5.. 0x0030: 0d00 0000 b7e0 f746 f13a 0e00 0000 0000 .......F.:...... 0x0040: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 0x0050: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 0x0060: 0000 0000 0000 0000 ........ 18:08:13.478497 IP6 2001:6f8:900:99d::2 > 2001:6f8:900:99d::1: ICMP6, echo reply, seq 6, length 64 0x0000: 6000 0000 0040 3a40 2001 06f8 0900 099d `....@:@........ 0x0010: 0000 0000 0000 0002 2001 06f8 0900 099d ................ 0x0020: 0000 0000 0000 0001 8100 4bb8 0435 0006 ..........K..5.. 0x0030: 0d00 0000 b7e0 f746 f13a 0e00 0000 0000 .......F.:...... 0x0040: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 0x0050: 0000 0000 0000 0000 0000 0000 0000 0000 ................ 0x0060: 0000 0000 0000 0000 ........ I think the route is set correctly: ip -6 route show 2001:6f8:900:99d::/64 via :: dev sixxs metric 256 expires 21322202sec mtu 1280 advmss 1220 hoplimit 4294967295 2000::/3 via 2001:6f8:900:99d::1 dev sixxs metric 1024 expires 21323306sec mtu 1280 advmss 1220 hoplimit 4294967295 fe80::/64 dev eth0 metric 256 expires 20580550sec mtu 1500 advmss 1220 hoplimit 4294967295 fe80::/64 via :: dev sixxs metric 256 expires 21322202sec mtu 1280 advmss 1220 hoplimit 4294967295 ff00::/8 dev eth0 metric 256 expires 20580550sec mtu 1500 advmss 1220 hoplimit 4294967295 ff00::/8 dev sixxs metric 256 expires 21322202sec mtu 1280 advmss 1220 hoplimit 4294967295 default via 2001:6f8:900:99d::1 dev sixxs metric 1024 expires 21322202sec mtu 1280 advmss 1220 hoplimit 4294967295 So anyone having an idea whats going on here? Greetz Sergius