[Asterisk-Users] SIP behind NAT, workaround to make W Snel's very welcome fix work both for inside *and* outside clients

[Christopher Stephens]

Hello everyone and welcome to my first post to the list!

After studying for a couple of weeks, I finally built * for the first
time last night, and of course had the same SIP-behind-NAT woes that
plague all of us who use NATted connections.
It was therefore with no small joy that I read the fix for that that
Walter Snel proposed (q.v.:
http://lists.digium.com/pipermail/asterisk-users/2003-October/024968.html).
Since I currently have no zaptel hardware (though intend to get some
within the week) and thus use soft (SIP) clients on the same internal
network, the caveat that it would break internal SIP clients was, for me,
a reason to not yet implement his fix. I was examining chan_sip.c, trying
to think of a way to implement his 'Naturally it would be much better to
make this behavior:', and while bemoaning my pathetic C skills, thought
of another solution:

-CUT HERE TO GET RIGHT TO THE POINT :P-
1) Somehow (I use dynamic DNS) get a FQDN to point to the IP of the
outside of your NAT box;
2) Implement W Snel's hardcoding as in the above URL, using your chosen
FQDN where, in his example, he has 213.84.4.39;
3) On any internal machine with a SIP client, add an entry to the hosts
file that points your chosen FQDN to the * server's IP on the *internal*
network.

What do you all think?
I won't have an opportunity to try to implement this until later this
evening, but at that time will post a follow-up to let you know how it
went.

-Chris