How does Linux choose which of possibly many IPv6 source addresses to use when connecting to another site? I am opening connections to 6to4 and non-6to4 sites from a host configured with both a 6to4 and a non-6to4 address.
My Linux box was configured with 6to4 and non-6to4 IPv6 addresses and it did indeed seem to pick the 6to4 source address when connecting to another 6to4 host, and the non-6to4 address when connecting to a non-6to4 host. This was faster because both directions of the 6to4 link were able to bypass the tunnel server. I wasn't sure if I was just getting lucky or if this was the expected behavior.
An iPad with the same IPv6 route advertisements chose to use IPv4 even when connecting to sites like ipv6.he.net, so I don't advertise the 6to4 route anymore. The local router still has its own 6to4 gateway to bypass the tunnel for outgoing 6to4.