Hi,
With great help from Jeroen Massars address independence patch posted to this list earlier this year, a first milestone of IPv6 support in tor was reached in the 0.2.3.9-alpha release. Clients can now connect to private bridges over IPv6 if configured for that. If you are at all interested in trying out the new IPv6 support, this short HOWTO is for you.
Please note that this is new code. Be prepared to run into bugs, hunt them down, report them, help out solve them and earn eternal fame and glory. It's a pain, but someone's got to do it.
As part of proposal 186 ("Multiple addresses for one OR or bridge"), the ORPort configuration option has changed and ORListenAddress will be deprecated. We can use this for adding an IPv6 address to a bridge already running on an IPv4 address. (Another option is to run a bridge listening _only_ to IPv6 but note that every relay need IPv4 too, in order to speak to other OR's in the Tor network.)
In order to configure a bridge to listen to an IPv6 address, add an ORPort option with an IPv6 address within square brackets and a port number like this:
ORPort [2001:DB8::42]:4711
In order to have your client connect to a bridge over IPv6, simply state the address of the bridge within square brackets and a port number in a Bridge line:
Bridge [2001:DB8::42]:4711
Note that there's still no support for IPv6 in BridgeDB. There is no harm in specifying PublishServerDescriptor 1 but nothing good will come out of it. You will have to find other ways of getting your bridge addresses to your users.
Note also that if you configure your client with two (or more) addresses belonging to the very same bridge, your client will pick one of them and try to use that. This behaviour is not perfect and will change in future versions of tor. This behaviour isn't even bug free and should not be counted on -- especially when an IPv6 address is preferred over an IPv4 address, in which case the IPv4 address in many cases is the one being used anyway. Short story: Don't configure your client with more than one address per bridge.
Please let me know if there are any questions about this and if you run in to any trouble setting it up. Then, when you run into the bugs, please go to https://trac.torproject.org/ and fire away.
Thanks, Linus