Code review comment for lp:~allenap/maas/regiond-bind-on-all-interfaces

I did a little experiment:

  >>> import socket
  >>> s = socket.socket(socket.AF_INET6, socket.SOCK_STREAM)
  >>> s.bind(('::', 0))
  >>> s.listen(50)
  >>> s.getsockname()
  ('::', 39025, 0, 0)

Okay, looks good.

  $ lsof -i TCP:39026
  COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
  ipython 71207 gavin 5u IPv6 492194 0t0 TCP *:39025 (LISTEN)

It doesn't show IPv4 there, but as Mike says, this is a compatibility
mode so I'm not entirely surprised.

Next, in another shell:

  $ telnet localhost 39025
  Trying 127.0.0.1...
  Connected to localhost.
  ...

At the same time:

  >>> s.accept()
  (<socket._socketobject at 0x7fc88bc41c20>, ('::ffff:127.0.0.1', 35080, 0, 0))

Okay, so the server sees an IPv4 address mapped into the IPv6 address
space.

Again, in another shell:

  $ telnet ::1 39025
  Trying ::1...
  Connected to ::1.
  ...

Again, at the same time:

  >>> s.accept()
  (<socket._socketobject at 0x7fc88a87d0c0>, ('::1', 43349, 0, 0))

No surprises here.