It is worse than that. The STUN taxonomy is brittle,
there are NATs
which feature different behaviour than anticipated in RFC3489.
Right. There is one we like to call the crap-nat. This nat changes the
source UDP port every few seconds. So once the media flow is
established it only works for 2-3 seconds until the nat switches to
another source port. Needles to say there is absolutely no way to make
VoIP work unders these conditions. We encounter one of these every few
weeks, and the only solution is to have the customer change the NAT
device he is using. (these are usually ADSL modems with inbuilt router)
--
Andres
Network Admin
http://www.telesip.net