STUN Binding request with local IP

Hello Everybody,

I am wondering if anybody can give me a hint what am I doing wrong?

I have a FreePBX Distro (Stable-3.211.63-10 Asterisk 11.4) up and running as one of multiple Virtual Servers on a single piece of HW.
I also do have an local DNS server running which is configured as the primary DNS server for all my virtual machines.

I followed all the guidelines I found on the internet about how to setup sip via Websocket but I just can not get it working.

To be specific: When using the sipML5 (or JsSip) client running on one of my servers, when I try to call *43 it from outside (internet) I am getting only one way audio. I can hear the Echo test, but I can not hear myself when testing. As soon as I connect to my local network via VPN, everything is fine.

I have analysed the network traffic and found out, that my remote IP (me using Web Softphone) is sending STUN Binding requests to my FreePBX local IP address.

I am using the following settins:

NAT = yes
IP Configuration = Static IP
External IP = MY.EX.IP.AD
fromdomain = my.freepbx.domain

On my Extension which I am using to login via the Websocket connection I also have

NAT = yes.

I do not understand what I am doing wrong when Asterisk is sending his local IP instead of the public one.

Thanks in advance. Much appreciated.