Hello, this a long-term problem which was happenning for me even on simbx01 so I do not think it is czprg01 specific. It is difficult to catch the problem as when one starts to play with IPv6 it "resurrects" and it works. But when the link is idle for ... hours? ... then it becomes unreachable. It is visible on the SixXS T58837 packetloss graph. On the mostly-client (source host) it is not a problem but on server (destination host) unreachable-after-being-idle is not acceptable. mailto:jan@jankratochvil.net source host is T57805, 6in4-static source host aiccu-2007.01.15-7.fc12.x86_64 (Fedora-14-x86_64) source host is behing openvpn with "virtual" public static IP 89.250.240.48 source host has small but continuous traffic https://www.sixxs.net/home/tunnelinfo/?57805 destination host is T58837, 6in4-static destination host aiccu-2007.01.15-7.el6.x86_64 (ScientificLinux-6.0-x86_64) destination host has real public static IP 46.28.109.124 (it is KVM guest) destination host has no IPv6 traffic now https://www.sixxs.net/home/tunnelinfo/?58837 no NATs should be in effect anywhere source host route -n -A inet6: Kernel IPv6 routing table Destination Next Hop Flags Metric Ref Use Iface 2a01:8c00:ff00:6::/64 :: U 256 8401 0 sixxs fe80::/64 :: U 256 0 0 eth0 fe80::/64 :: U 256 0 0 sixxs ::/0 2a01:8c00:ff00:6::1 UG 1024 91912 2 sixxs ::1/128 :: U 0 517730 7 lo 2a01:8c00:ff00:6::2/128 :: U 0 1890355 1 lo fe80::59fa:f030/128 :: U 0 0 1 lo fe80::21f:d0ff:feda:d892/128 :: U 0 0 1 lo ff00::/8 :: U 256 0 0 eth0 ff00::/8 :: U 256 0 0 sixxs destination host route -n -A inet6: Kernel IPv6 routing table Destination Next Hop Flags Metric Ref Use Iface 2a01:8c00:ff00:5d::/64 :: U 256 540 0 sixxs fe80::/64 :: U 256 0 0 eth0 fe80::/64 :: U 256 0 0 sixxs ::/0 2a01:8c00:ff00:5d::1 UG 1024 849 1 sixxs ::1/128 :: U 0 720 1 lo 2a01:8c00:ff00:5d::2/128 :: U 0 27264 1 lo fe80::2e1c:6d7c/128 :: U 0 0 1 lo fe80::5054:ff:fe00:270/128 :: U 0 0 1 lo ff00::/8 :: U 256 0 0 eth0 ff00::/8 :: U 256 0 0 sixxs 2a01:8c00:ff00:6::2$ ping6 2a01:8c00:ff00:5d::2 PING vps(vps.jankratochvil.net) 56 data bytes From gw-7.prg-01.cz.sixxs.net icmp_seq=2 Destination unreachable: Address unreachable From gw-7.prg-01.cz.sixxs.net icmp_seq=3 Destination unreachable: Address unreachable From gw-7.prg-01.cz.sixxs.net icmp_seq=4 Destination unreachable: No route From gw-7.prg-01.cz.sixxs.net icmp_seq=5 Destination unreachable: No route From gw-7.prg-01.cz.sixxs.net icmp_seq=6 Destination unreachable: No route From gw-7.prg-01.cz.sixxs.net icmp_seq=7 Destination unreachable: No route From gw-7.prg-01.cz.sixxs.net icmp_seq=8 Destination unreachable: No route From gw-7.prg-01.cz.sixxs.net icmp_seq=9 Destination unreachable: No route From gw-7.prg-01.cz.sixxs.net icmp_seq=10 Destination unreachable: No route From gw-7.prg-01.cz.sixxs.net icmp_seq=11 Destination unreachable: No route From gw-7.prg-01.cz.sixxs.net icmp_seq=12 Destination unreachable: No route From gw-7.prg-01.cz.sixxs.net icmp_seq=13 Destination unreachable: No route From gw-7.prg-01.cz.sixxs.net icmp_seq=14 Destination unreachable: No route From gw-7.prg-01.cz.sixxs.net icmp_seq=15 Destination unreachable: No route From gw-7.prg-01.cz.sixxs.net icmp_seq=16 Destination unreachable: No route From gw-7.prg-01.cz.sixxs.net icmp_seq=17 Destination unreachable: No route From gw-7.prg-01.cz.sixxs.net icmp_seq=18 Destination unreachable: No route From gw-7.prg-01.cz.sixxs.net icmp_seq=19 Destination unreachable: No route From gw-7.prg-01.cz.sixxs.net icmp_seq=20 Destination unreachable: No route From gw-7.prg-01.cz.sixxs.net icmp_seq=21 Destination unreachable: No route From gw-7.prg-01.cz.sixxs.net icmp_seq=22 Destination unreachable: No route From gw-7.prg-01.cz.sixxs.net icmp_seq=23 Destination unreachable: No route From gw-7.prg-01.cz.sixxs.net icmp_seq=24 Destination unreachable: No route From gw-7.prg-01.cz.sixxs.net icmp_seq=25 Destination unreachable: No route From gw-7.prg-01.cz.sixxs.net icmp_seq=26 Destination unreachable: No route From gw-7.prg-01.cz.sixxs.net icmp_seq=27 Destination unreachable: No route From gw-7.prg-01.cz.sixxs.net icmp_seq=28 Destination unreachable: No route From gw-7.prg-01.cz.sixxs.net icmp_seq=29 Destination unreachable: No route From gw-7.prg-01.cz.sixxs.net icmp_seq=30 Destination unreachable: No route From gw-7.prg-01.cz.sixxs.net icmp_seq=31 Destination unreachable: No route From gw-7.prg-01.cz.sixxs.net icmp_seq=32 Destination unreachable: No route 64 bytes from vps.jankratochvil.net: icmp_seq=33 ttl=63 time=23.7 ms 64 bytes from vps.jankratochvil.net: icmp_seq=34 ttl=63 time=23.6 ms 64 bytes from vps.jankratochvil.net: icmp_seq=35 ttl=63 time=23.0 ms 64 bytes from vps.jankratochvil.net: icmp_seq=36 ttl=63 time=22.8 ms 64 bytes from vps.jankratochvil.net: icmp_seq=37 ttl=63 time=22.0 ms ^C --- vps ping statistics --- 37 packets transmitted, 5 received, +31 errors, 86% packet loss, time 36059ms rtt min/avg/max/mdev = 22.071/23.097/23.793/0.647 ms source host$ traceroute6 destination-host traceroute to vps (2a01:8c00:ff00:5d::2), 30 hops max, 80 byte packets 1 gw-7.prg-01.cz.sixxs.net (2a01:8c00:ff00:6::1) 19.613 ms 27.670 ms 35.482 ms 2 vps.jankratochvil.net (2a01:8c00:ff00:5d::2) 57.427 ms !X 59.077 ms !X 73.256 ms !X That !X is from: 08:03:21.117522 IP6 2a01:8c00:ff00:6::2.56077 > 2a01:8c00:ff00:5d::2.33452: UDP, length 32 08:03:21.138698 IP6 2a01:8c00:ff00:5d::2 > 2a01:8c00:ff00:6::2: ICMP6, destination unreachable, unreachable prohibited 2a01:8c00:ff00:5d::2, length 88 due to the default (with some ports allowed) RHEL-6.0 (ScientificLinux-6.0) firewall: destination host ip6tables -L Chain INPUT (policy ACCEPT) target prot opt source destination ACCEPT all ::/0 ::/0 state RELATED,ESTABLISHED ACCEPT icmpv6 ::/0 ::/0 ACCEPT all ::/0 ::/0 ACCEPT tcp ::/0 ::/0 state NEW tcp dpt:22 ACCEPT tcp ::/0 ::/0 state NEW tcp dpt:80 ACCEPT tcp ::/0 ::/0 state NEW tcp dpt:21 ACCEPT tcp ::/0 ::/0 state NEW tcp dpt:25 ACCEPT tcp ::/0 ::/0 state NEW tcp dpt:53 ACCEPT udp ::/0 ::/0 state NEW udp dpt:53 ACCEPT tcp ::/0 ::/0 state NEW tcp dpt:993 ACCEPT tcp ::/0 ::/0 state NEW tcp dpt:9418 REJECT all ::/0 ::/0 reject-with icmp6-adm-prohibited Chain FORWARD (policy ACCEPT) target prot opt source destination REJECT all ::/0 ::/0 reject-with icmp6-adm-prohibited Chain OUTPUT (policy ACCEPT) target prot opt source destination destination host table mangle is empty/ACCEPT. source host$ traceroute -n 217.31.57.16 # czprg01 IPv4 1 192.168.240.48 17.601 ms 25.492 ms 30.760 ms 2 89.250.240.149 38.056 ms 43.912 ms 50.618 ms 3 89.250.240.34 57.067 ms 63.417 ms 70.099 ms 4 109.205.72.241 84.242 ms 84.953 ms 89.372 ms 5 194.50.100.4 96.765 ms 102.700 ms 109.650 ms 6 217.31.48.98 120.030 ms 104.972 ms 109.149 ms 7 217.31.57.16 105.248 ms 103.893 ms 104.659 ms source host$ ifconfig tun1 # the IPv4 openvpn link tun1 Link encap:UNSPEC HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00 inet addr:89.250.240.48 P-t-P:192.168.240.48 Mask:255.255.255.255 UP POINTOPOINT RUNNING NOARP MULTICAST MTU:1500 Metric:1 RX packets:30980042 errors:0 dropped:0 overruns:0 frame:0 TX packets:20413693 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:100 RX bytes:32507548124 (30.2 GiB) TX bytes:1985484513 (1.8 GiB) destination host$ traceroute -n 217.31.57.16 # czprg01 IPv4 traceroute to 217.31.57.16 (217.31.57.16), 30 hops max, 60 byte packets 1 46.28.109.1 0.235 ms 0.224 ms 0.266 ms 2 46.28.104.5 0.399 ms 0.374 ms 0.569 ms 3 94.124.104.77 3.866 ms 3.806 ms 3.789 ms 4 94.124.104.101 17.268 ms 17.129 ms 17.018 ms 5 194.50.100.8 5.092 ms 5.018 ms 5.310 ms 6 217.31.57.16 4.013 ms 3.844 ms 3.756 ms Thanks.