I'm trying to enable IPv6 since my new ISP (CenturyLink) supports. When I do, however, I am unable to connect to half the websites I visit, even if they're well known and well developed. (Yahoo.com goes down with IPv6 enabled, for example.) I can also connect to some dual-stacked, IPv4-only, and IPv6-only sites without issue, so it seems random on which websites work. Internet tests such as http://test-ipv6.com/ return saying everything is good.

Modem Model: ZyXEL C1000Z

IPv4 DHCP Settings:

Public IP:
DNS Server #1:
DNS Server #2:

IPv6 DHCP Settings:

Public IP: 2602:47:d65e:acff::1/64
DNS Address #1: 2001:4860:4860::8888
DNS Address #2: 2001:4860:4860::8844


david@Galadhriel:~$ ifconfig
eth0      Link encap:Ethernet  HWaddr 80:fa:5b:03:f0:a6  
          inet addr:  Bcast:  Mask:
          inet6 addr: 2602:47:d65e:ac00:82fa:5bff:fe03:f0a6/64 Scope:Global
          inet6 addr: fd00::d443:bb75:cbbe:b105/64 Scope:Global
          inet6 addr: 2602:47:d65e:ac00:d443:bb75:cbbe:b105/64 Scope:Global
          inet6 addr: fd00::82fa:5bff:fe03:f0a6/64 Scope:Global
          inet6 addr: fe80::82fa:5bff:fe03:f0a6/64 Scope:Link
          RX packets:53121 errors:0 dropped:0 overruns:0 frame:0
          TX packets:495685 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:62033716 (62.0 MB)  TX bytes:38657577 (38.6 MB)
          Interrupt:20 Memory:f7e00000-f7e20000 

lo        Link encap:Local Loopback  
          inet addr:  Mask:
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:538876 errors:0 dropped:0 overruns:0 frame:0
          TX packets:538876 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:32106042 (32.1 MB)  TX bytes:32106042 (32.1 MB)

wlan0     Link encap:Ethernet  HWaddr a0:a8:cd:67:88:38  
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:806 errors:0 dropped:0 overruns:0 frame:0
          TX packets:601 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:320472 (320.4 KB)  TX bytes:84286 (84.2 KB)

What am I missing here?

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  • Pick one that fails, and check whether you're getting a v4 or v6 address from DNS. Try a traceroute to the IP and see where you stop. – Ron Trunk Aug 8 '14 at 18:54
  • The traceroutes and pings are working perfectly. The website whatismyv6.com shows that I'm connecting using an IPv4 address. Their IPv6-only site doesn't work in the web browser, but can still be pinged. – vroomhenderson Aug 8 '14 at 20:29
  • Check your Zyxel router. It's already doing one bad thing I can see, that is, assigning a stupid unique local address prefix (this should be set randomly, but yours is fixed as fd00::/48). Try resetting it to factory, or updating its firmware. – Michael Hampton Nov 16 '14 at 7:59

It could be that you have a problem with IPv6 Path MTU Discovery. This might be due to overly restrictive firewall settings on your computer or your router, discarding ICMPv6 Packet Too Big messages. I am not sure if it would spot the problem, but I would suggest testing your connection with a site like http://test-ipv6.com/ that does a bit more than just show your IPv6 address.

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