Hi Juliusz,

Thanks for your help.
See below for a simple setting that works with our external coturn.

The problem is probably that your NAT doesn't implement hairpinning, so
Galène and the TURN server cannot communicate.
 Coturn is probably
connecting over IPv6, which the built-in server doesn't handle.

I have deactivated the IPV6 everywhere and double checked (inspecting about:websocket) in Firefox that it does not use IPV6.

Could you please check Galène's log for mentions of a relay test?  If the
server-side relay test (the one in Galène's log) fails, that's probably
indicative of a problem with hairpinning.

Server side : the relay-test do not fails.

Client side : 
   - using the builtin turn, the relay test fails , 
   - using coturn (on the same server) it works.

Fabrice — if your instance of Galène is behind NAT, then I strongly
recommend running an instance of coturn on a host that is not behind NAT.

The following works : 

- port forwarding from my router (Freebox) to a Linux 20.04  VM (virtual box) : 

   49152-65535 (UDP/TCP)
   3478 (UDP/TCP) 
   8443 (UDP/TCP) 

- coturn on the VM with the following configuration

  listening-port=3478
  fingerprint
  lt-cred-mech
  user=<TURN USER>:<TURN PASSWD>
  server-name=<TURN SERVER NAME>
  realm=<DOMAINE>

- galene on the VM launched with the option -turn auto 
  and data/ice-servers.json with the following contents

[
    {
        "Urls": [
            "turn:<TURN SERVER NAME>:3478",
            « turn:<TURN SERVER NAME>:3478?transport=tcp"
        ],
        "username": "<TURN USER>",
        "credential": "<TURN PASSWD>"
    }
]