# ip6 -a # sysctl -w net.inet6.ip6.accept_rtadv=1
The first command was mentioned on a blog post as needed to “fully enable IPv6 features, beyond what is enabled via the Control Panel”. The second command enables the acceptance of IPv6 Router Advertisements.
This turns out to NOT be be needed at all. I did a complete new Snow Leopard install from the DVD this evening on a spare MacBook Pro, and everything IPv6 worked perfectly, out of the box. IPv6 was enabled by default, and fast visits to test-ipv6.com and ipv6-test.com showed full native IPv6 connectivity.
I can only surmise that somewhere along the way, my regular MacBook Pro had had IPv6 turned off in some unusual way. Or it could be that my original MacBook Pro was originally a Leopard install, which was upgraded to Snow Leopard.
So, MacOS X Snow Leopard completely IPv6 ready, out of the box. I’ll be testing Lion in January…