Stun Server Firewall Test Failure

[SonikIT]

Using 3CX server on VOIP-Unlimited ADSL through a Vigor 2800 Router.
Snom 300 & 360 Phones
We occasionally get very bad VOIP connections, which often drop by thenselves or are unuseable quality.

The ports are all defined as open ports for the SIP, STUN settings. But we constantly get the Firewall test to fail with;
Error (4) The STUN server returned an ip which is not accessible from outside. addrFromSTUN = ip:9002

The draytek router is performing one-to-one nat from the diagnostics. We have a 20-1 ADSL supplier with 800k/7.6m ADSL speed. Only VOIP traffic goes out on the ADSL.

We have aslo tried several stun servers

Any ideas out there

 

[commplete]

We have an almost identical setup and problem.

Using a 3CX with Voip Unlimited, draytek vigor 2820.
We often get very bad voip connections, and frequent one way/silent voip calls.

The firewall checker also frequently reports error, although sometimes it passes.

Archie from 3CX, kindly replied to one of by questions as follows, it points to maybe the Draytek not providing one-to-one nat, but symetrical .

"3CX PBX doesn't have STUN server. So it doesn't expect port 3478 to be opened for incoming. But it has STUN client which sends requests to external STUN servers, which usually set at port 3478. So if your router doesn't disable sending to that port - it's enough.
Still, your SIP port (5060) and RTP range of ports should be mapped properly on router to have stable solution. Symmetric NAT is not supported (it may still work, but gives extremely unstable results). The error from your firewall check hints that you have symmetric NAT mapping."