Asus RT-N56U (IPv6 lost internet)

[astronyu]

My tunnel endpoint is a router running stock firmware version:3.0.0.4.334. The router advertises the IPv6 to the LAN using radvd.
So far my PC running Windows 8 and my Macbook Pro have no problem receiving IPv6.

BUT..a little while ago IPv6 stopped working. I couldn't open any IPv6 websites, even on my system tray network notification shows IPv6 Connectivity as No Internet Connection.
Is it because of the Anycast Caching Nameserver being down?

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Windows IP Configuration

   Host Name . . . . . . . . . . . . : RXXXh-PC
   Primary Dns Suffix  . . . . . . . :
   Node Type . . . . . . . . . . . . : Hybrid
   IP Routing Enabled. . . . . . . . : No
   WINS Proxy Enabled. . . . . . . . : No
   DNS Suffix Search List. . . . . . : XXX

Ethernet adapter Local Area Connection 6:

   Connection-specific DNS Suffix  . : XXX
   Description . . . . . . . . . . . : Realtek PCIe GBE Family Controller
   Physical Address. . . . . . . . . : XXX
   DHCP Enabled. . . . . . . . . . . : Yes
   Autoconfiguration Enabled . . . . : Yes
   IPv6 Address. . . . . . . . . . . : XXX(Pref
erred)
   Temporary IPv6 Address. . . . . . : XXX(Pref
erred)
   Link-local IPv6 Address . . . . . : fe80::21e3:631a:da53:60b1%12(Preferred)
   IPv4 Address. . . . . . . . . . . : 192.168.1.101(Preferred)
   Subnet Mask . . . . . . . . . . . : 255.255.255.0
   Lease Obtained. . . . . . . . . . : 11 Februari 2013 4:55:09 PM
   Lease Expires . . . . . . . . . . : 12 Februari 2013 4:55:09 PM
   Default Gateway . . . . . . . . . : fe80::3285:a9ff:fe6a:4825%12
                                       192.168.1.1
   DHCP Server . . . . . . . . . . . : 192.168.1.1
   DHCPv6 IAID . . . . . . . . . . . : 555511653
   DHCPv6 Client DUID. . . . . . . . : XXX-1B-CF

   DNS Servers . . . . . . . . . . . : 2001:470:20::2
                                       2001:4860:4860::8888
                                       2001:4860:4860::8844
                                       8.8.8.8
                                       192.168.1.1
   Primary WINS Server . . . . . . . : 192.168.1.1
   NetBIOS over Tcpip. . . . . . . . : Enabled

Tunnel adapter isatap.XXX:

   Media State . . . . . . . . . . . : Media disconnected
   Connection-specific DNS Suffix  . : XXX
   Description . . . . . . . . . . . : Microsoft ISATAP Adapter #2
   Physical Address. . . . . . . . . : 00-00-00-00-00-00-00-E0
   DHCP Enabled. . . . . . . . . . . : No
   Autoconfiguration Enabled . . . . : Yes


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Idx     Met         MTU          State                Name
---  ----------  ----------  ------------  ---------------------------
  1          50  4294967295  connected     Loopback Pseudo-Interface 1
14          50        1280  disconnected  isatap.XXX
12          10        1480  connected     Local Area Connection 6

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admin@RT-N56U:/tmp/home/root# ping6 2001XXX:2
PING 2001XXX:2 (2001XXX:2): 56 data bytes

--- 2001:470:20::2 ping statistics ---
13 packets transmitted, 0 packets received, 100% packet loss

admin@RT-N56U:/tmp/home/root# ping6 2001XXX:2
PING 2001XXX:2 (2001XXX:2): 56 data bytes
64 bytes from 2001XXX:2: seq=0 ttl=64 time=0.657 ms
64 bytes from 2001XXX:2: seq=1 ttl=64 time=0.381 ms
64 bytes from 2001XXX:2: seq=2 ttl=64 time=0.382 ms

--- 2001:470:18:11ab::2 ping statistics ---
3 packets transmitted, 3 packets received, 0% packet loss
round-trip min/avg/max = 0.381/0.473/0.657 ms

admin@RT-N56U:/tmp/home/root# ping6 2001:470:18:11ab::1
PING 2001XXX:1 (2001XXX:1): 56 data bytes

--- 2001:470:18:11ab::1 ping statistics ---
11 packets transmitted, 0 packets received, 100% packet loss


[kasperd]

Is it because of the Anycast Caching Nameserver being down?

That is probably not the reason. Problems reaching your name server should affect access to IPv4 and IPv6 sites alike, thus the symptoms you describe don't sound like a name server being down.

The symptoms are however consistent with your tunnel being down. If your tunnel is down, it will break access to the caching name server over IPv6. It will also break access to IPv6 sites. Additionally it will break any ping6 command that would traverse the tunnel. The ping commands you posted show that you can ping your local side of the tunnel, but not the tunnel server side of the tunnel. I conclude your problem is that your tunnel is down.

First step in debugging a tunnel that is down is to do an IPv4 traceroute towards the IPv4 address of the tunnel server (216.218.221.6 in your case as far as I can tell).

Problems with the anycast DNS server not responding do happen. I configured my own network to fallback to unicast to another DNS server. In a pool of anycast DNS servers each of them must also have a unicast address. You can find out the unicast address of the DNS server you are currently using by looking up the AAAA record for mydnsv6.kasperd.net.