On a recent build I ran in to the following error messages:
Wed May 3 14:31:43 2017 /sbin/ip -6 addr add 2001:db8:0:4::1/64 dev tun0
Wed May 3 14:31:43 2017 Linux ip -6 addr add failed: external program exited with error status: 2
This appears to be do to the fact that somewhere something defaulted the
kernel in the container to disable IPv6. Not sure if this is my host or
the docker daemon. Re-enable it explicitly for now until Docker gets
it's IPv6 act together.