[Freeswitch-users] NAT traversal - the final say..!

peely freeswitch at peely.com
Thu Jan 3 19:12:30 MSK 2013

IMO as a provider, FS does an excellent job at detecting NAT on its own and
handling it. We've rarely had any issue with our end sending INVITEs to the
wrong place or one / no way speech. connectile dysfunction does nothing
more. The only switch we enable is one to enable the SIP options ping and to
use sip-force-expires to reduce the time the endpoint re-registers for
mobile devices.

As with others on this thread, the ALG in most routers is the culprit, I've
rarely experienced one which does anything beneficial, most screw up the

We also recommend that customers change the SIP port on their handsets to
anything other than 5060, older BT routers especially seem to stop
forwarding responses after a few minutes, again as they have a very basic
ALG. Using port forwarding in the router is the only sure fire way of
getting reliable SIP through to a handset, Draytek routers seem to be pretty
flaky until you do this or use TCP / TLS.

If the router stops forwarding packets because of a poor ALG implementation
or other firewall rules, nothing FS can do will overcome this.

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