I looked at a couple of other sites: you might try this one: http://forums.comcast.com/t5/Home-Networking-Router-WiFi/Evidence-of-Comcast-IPv6-CPE-Dual-Stack-CPE-and-CPEPD/td-p/1295481/page/3
If you're a residential user you really shouldn't need v6 yet. You should be able to get to most everything people use with v4 still. If you truly must have v6 due to sites you're connecting to that are v6-only then I'd go back to 6to4 tunnel. If you get lots of errors or cannot connect I'd e-mail netgear. I've had good luck with them.
Oh, I did see this on one of the sites:
But there was one last hurdle: Comcast. While IPs had configured fine, I couldn’t reach anywhere. I spent roughly 30 minutes reviewing all configuration settings, making sure I had routes, and rebooting everything a few times to no avail. Finally gave in, called back Comcast, and the tech was like “oh, let me disable the firewall on our side.” POOF! Everything worked. So Comcast residential IPv6 is definitely live in my area, and just needed a new shiny DOCSIS 3.x modem.
and this - which I've had issues with and I use a netgear wnr2000v3:
Forums indicated that a common issue is that routers/modems have incompatible asynchronous boot up sequences, e.g. IPv6 is ready on one before the other and they establish DHCP improperly as a result.
What (I think) eventually worked for me was turning off both, allowing the router to fully boot and wait a FULL couple of minutes, then boot up the modem, which will then realize it needs IPv6 for a whole network not just one client. My interpretation of what happened, at least.
I happen to also have turned on IPv6 ULA when I did this, but that does not appear to be getting utilized from what I can tell. I’m not even clear what that does.
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