That's very, very, very strange. I've been running IPv6 (first through a tunnelbroker.net tunnel, and -much- later using native IPv6 through Comcast) for roughl

That's very, very, very strange. I've been running IPv6 (first through a tunnelbroker.net tunnel, and -much- later using native IPv6 through Comcast) for roughly eight years now. Haven't had any issue with Linux, Mac, or Windows systems. To diagnose a thing, what happens when you disable Router Advertisements on your router, then enable IPv6 on a machine, and run Teredo [0] on that machine? (After Teredo assigns an IPv6 address to the teredo virtual interface, start a 'ping6 google.com'. It will take a few minutes for the Teredo machinery to figure out how to make a connection, but it should eventually do so.) Are you -perhaps- rejecting or dropping ICMP on your router? If you are, don't. ICMP is required to make IPv6 work. [0] This is the Teredo implementation that people use on Linux systems http://www.remlab.net/miredo/ http://www.remlab.net/miredo/