I have a heartbeat tunnel from Concepts ICT BV. Have worked fine since I got it setup. Endpoint has changed multiple times (faulty line I think. Have contacted ISP about this) Anyways. I recently got another IP, so I run the commands again to setup the tunnel. My server isn't the router, so I use static NAT. Always worked before, from different providers. But, no connection to any IPv6-host. Not my gateway, not anything. So I try to reboot. Still no effect. The heartbeat client is always running, and sendt a few packets before I tried to setup again, just to make sure it got updated. I've read that it's important to include lots of (relevant) information, so I post some output from various commands commands used to setup tunnel: ip tunnel add sixxs mode sit local 10.0.0.3 remote 213.197.27.252 ip link set sixxs up ip link set mtu 1280 dev sixxs ip tunnel change sixxs ttl 64 ip -6 addr add 2001:838:300:1cf::2/64 dev sixxs ip -6 ro add default via 2001:838:300:1cf::1 dev sixxs no errors are returned. Only when trying to use my endpoint instead of 10.0.0.3, then I get "ioctl: No buffer space available" ping to my gateway: # ping6 2001:838:300:1cf::1 PING 2001:838:300:1cf::1(2001:838:300:1cf::1) 56 data bytes --- 2001:838:300:1cf::1 ping statistics --- 7 packets transmitted, 0 received, 100% packet loss, time 5999ms tcpdump: # tcpdump -i sixxs tcpdump: WARNING: sixxs: no IPv4 address assigned tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on sixxs, link-type RAW (Raw IP), capture size 96 bytes 23:25:50.620244 cl-464.ams-01.nl.sixxs.net > gw-464.ams-01.nl.sixxs.net: icmp6: echo request seq 5 23:25:51.622045 cl-464.ams-01.nl.sixxs.net > gw-464.ams-01.nl.sixxs.net: icmp6: echo request seq 6 23:25:52.621819 cl-464.ams-01.nl.sixxs.net > gw-464.ams-01.nl.sixxs.net: icmp6: echo request seq 7 23:25:53.621633 cl-464.ams-01.nl.sixxs.net > gw-464.ams-01.nl.sixxs.net: icmp6: echo request seq 8 23:25:54.621434 cl-464.ams-01.nl.sixxs.net > gw-464.ams-01.nl.sixxs.net: icmp6: echo request seq 9 23:25:55.621274 cl-464.ams-01.nl.sixxs.net > gw-464.ams-01.nl.sixxs.net: icmp6: echo request seq 10 Lots of traffic going out, but nothing ever comes back in :/ Anyone who knows what might be wrong? Or something I could check?