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 <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>"
    }
]