Construct the tunnel as a separate phase

[vanrein]

Look at what Tayga does, it has an explicit --mktun command to do nothing but creating the tunnel. This is useful to run as root, especially because tools to do this are getting less common in user space.

[vanrein]

Especially interesting is that this usage pattern allows the setup of the network interface by external code, not the builtin ip -6 ... commands that we now need to use. That could greatly simplify our use.

Sure, some information may be derived by the 6bed4router, but that information might then be returned from the --mktun command, perhaps as ENVVAR=value lines or even just the ip -6 ... commands.

[vanrein]

Maybe the best thing to do is ensure having the tunnel, not making it. Dropping it could be useful too.

[vanrein]

For the TAP mode of #9 it might be good to also have a --mktap or --have-tap variant.

There may be no need to configure if a bridge is used or, dependent on the local setup, configuration may be redirected to a bridge.