Hello, Once every few weeks I receive an email about my tunnels downtime. The tunnel is T121674. Last time this happened on Dec 23 but only today I could look into the issue. So it seems that my side of the tunnel was not resonding to pings since around Dec 21. But Im pretty sure that my side of tunnel is up and no configurations changes were made for at least a month or so. I used my IPv6-capable VPS from the other part of the Earth (blua.kir.elagin.me) to ping the gateways endpoint (2a02:578:5002:c7::1) and it was responding. Then I started pinging my tunnel endpoint (2a02:578:5002:c7::2) and it was NOT responding. Still pinging I started `tcpdump -i sixxs` on my host to check packets going through the virtual interface and there were no packets. Then I pinged the gateways endpoint from the host that is my endpoint. And here is what I saw in tcpdump: ~~~~~ tcpdump: WARNING: sixxs: no IPv4 address assigned error : ret -1 tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on sixxs, link-type RAW (Raw IP), capture size 65535 bytes # # Silence until I pinged the tunnel from my side # 18:41:57.130295 IP6 cl-200.led-01.ru.sixxs.net > gw-200.led-01.ru.sixxs.net: ICMP6, echo request, seq 1, length 64 18:41:57.131545 IP6 gw-200.led-01.ru.sixxs.net > cl-200.led-01.ru.sixxs.net: ICMP6, echo reply, seq 1, length 64 18:41:57.319875 IP6 blua.kir.elagin.me > cl-200.led-01.ru.sixxs.net: ICMP6, echo request, seq 109, length 64 18:41:58.132042 IP6 cl-200.led-01.ru.sixxs.net > gw-200.led-01.ru.sixxs.net: ICMP6, echo request, seq 2, length 64 18:41:58.133024 IP6 gw-200.led-01.ru.sixxs.net > cl-200.led-01.ru.sixxs.net: ICMP6, echo reply, seq 2, length 64 18:41:58.320479 IP6 blua.kir.elagin.me > cl-200.led-01.ru.sixxs.net: ICMP6, echo request, seq 110, length 64 18:41:59.133481 IP6 cl-200.led-01.ru.sixxs.net > gw-200.led-01.ru.sixxs.net: ICMP6, echo request, seq 3, length 64 18:41:59.134585 IP6 gw-200.led-01.ru.sixxs.net > cl-200.led-01.ru.sixxs.net: ICMP6, echo reply, seq 3, length 64 18:41:59.321640 IP6 blua.kir.elagin.me > cl-200.led-01.ru.sixxs.net: ICMP6, echo request, seq 111, length 64 # and so on ~~~~~ As you can see exactly the moment I pinged the gateway from my side I started receiving echo requests from my remote VPS. So the question is: whats going on? Is it some kind of misconfiguration on my side or on the gateways side? ~~~~~ # uname -a Linux verda.kir.elagin.me 3.9.5-hardenedverda #2 SMP Thu Nov 27 15:36:10 MSK 2014 x86_64 Intel(R) Core(TM)2 CPU 6300 @ 1.86GHz GenuineIntel GNU/Linux # ip a s sixxs 8: sixxs: <POINTOPOINT,NOARP,UP,LOWER_UP> mtu 1280 qdisc noqueue state UNKNOWN link/sit 10.188.37.24 peer 77.109.111.178 inet6 2a02:578:5002:c7::2/64 scope global valid_lft forever preferred_lft forever inet6 fe80::abc:2518/128 scope link valid_lft forever preferred_lft forever ~~~~~