[Users] requirement of using mediaproxy

[unplug]

I am using the features-callfwd.cfg script with mediaproxy in a
testing server.  I can make call directly from phone to phone and
forward call.  However, it is failed to forward call on no answer and
forward call on busy.  In my testing server, it only has a network
interface.  I wonder if it is the cause of the problem.  Does it need
to have 2 network interfaces (one for external and one for internal)
for those forward features work?