I'm at my parents' now and trying to figure out why IPv6 isn't working. They have Comcast, and their router is an Asus RT-N16 running Toastman's newest Tomato firmware.

The modem is in bridge mode yet its admin screen shows it getting its own IPv4 and IPv6 addresses - potentially for phone service, which my parents also have through Comcast. Not sure.

In any case, the router gets a totally different IPv4 address than the modem, and doesn't get any IPv6 address. I have the router set to use DHCPv6 with prefix delegation, and to accept RA from the WAN.

Any ideas? I thought Comcast had IPv6 running on its entire network.

Thanks!

Tried this? http://mydeviceinfo.comcast.net/download.php?file_id=31

Yep, no difference

Comcast does have IPv6 on their entire residential network, they've been touting that for a year or two.

There are several ways they have to check and test, (quick way, more, see RH column here). Sounds like in your case you want to break it down and see if the problem is your modem or router or the hosts.

To check IPv6 to the modem, disconnect the network cable between modem & router, reboot the modem (that means power it down and power back up). When the modem has rebooted and is online, connect the network cable directly from the modem to your PC. You should get an IPv6 address within about 30 seconds of connecting the network cable.

That is a purpose built test Comcast uses, their servers detect a single host and give it one IPv6 address, a so-called /128. I forget the actual details, but you may get more than one address, a link local/fe80...:, and one permanent and one temporary global/unicast, 2601.... If your host gets this, then obviously IPv6 works to the cable modem.

For a home gateway/router, the correct settings are:
WAN side:
- Enable DHCPv6 on the WAN.
On the LAN side:
- Enable SLAAC, and PD (prefix delegation enabled). Sometimes the PD settings are on the wan side. Use a prefix size of 64.
- You also need DHCP enabled on the WAN side (although it's not used the same way as IPv4), and set the "other flag", and disable the "managed flag." This is how some values get from the router to the hosts, such as IPv6 DHCP servers, IPv6 default gateway, etc.
- Enable RADVD, the commonly used acronym for Router Advertisement Daemon.
- Don't enter any advertisement prefixes, the router will get these from the WAN side.

Reply back if you get stuck.

Hey JadedTraveler, thanks. So, I'm a little embarrassed to admin that things were more or less working the whole time. I had been looking for an IPv6 address in the router's WAN status, but it shows it in LAN...

So now I have a different question. When I use mobile safari to go to test-IPv6.com, I get 10/10 every time. But when I use iOS Chrome, about half the time it says I have MTU problems and need to ensure ICMP packet too big messages are enabled. Could this be Chrome tunneling things to google over IPv4? I don't have a packet too big setting in the router.

I have the boxes checked for "announce IPv6 on LAN" for both DHCP and SLAAC.

gunkdave, I've seen the same message on occasion, never figured out what causes it, and after 30 mins or so I would not get it.

I don't think browsers, any browser, tunnels 6 to 4. Tunneling can be setup, but it's at a different layer than a browser, and you only want it when you don't have IPv6. Browsers use "dual stack" meaning theu lookup a url in IPv6 first, if not found they look for IPv4. This is configurable (and a simplified explanation), but you don't want to change the default.

There are multiple ipv6 test sites, see the mirrors and check if you get the mtu message on all of them. The site ipv6.test-ipv6.com is a special one, it's the parent of all the other ones, and it's 6 only.

Comcast's speedtest does both ipv4 and ipv6, it's another simple, and pretty cool way to see if everything is working correctly.