To add to what Ineblett mentioned above regarding SIP and RTP ports used for remote extensions, kindly notice that each Remote STUN Extension must have a unique Local SIP Port and Unique RTP Port range.
In the provisioning tab of each extension make sure that the Local SIP Port of Phone is different between the extensions that you have selected to register through STUN method and are behind the same Public ip address (1st 5065, 2nd 5066, 3rd 5067, etc… ) as well the Local RTP Audio Ports Start ( 1st14000-140011, 2nd 14012-14023, 3rd 14024-14035, etc… )
Make sure that since each phone has dedicated ports, on the remote firewall you have to make a Static NAT and Static Port Forwarding to the Private ip address of each phone. If you are using Yealink phones and these are on firmware x.80.x.x then you will need 12 RTP ports for each extension.
- In the Management Console each Remote STUN Extensions must have a unique Local SIP Port and Unique RTP Port range and the RTP Port range must be 10 ports (for Yealink phones 12 ports) per remote site. This means that if we only had Yealink phones that would be e.g.:
- Ext A should have Local SIP Port: 5065 and RTP Port Range: 14000-14011 (12 ports)
- Ext B should have Local SIP Port: 5066 and RTP Port Range: 14012-14023 (12 ports)
- Ext C should have Local SIP Port: 5067 and RTP Port Range: 14024-14035 (12 ports)
- Once you have done this, then on the Remote Location Router/Firewall behind which the phones are residing, you must:
Disable SIP ALG or any similar port remapping feature.
Create NAT/Port Forwarding Rules so that, as per the above example:
— Ports 5065 TCP/UDP and 14000-14011 UDP are forwarded to the IP of Ext A
— Ports 5066 TCP/UDP and 14012-14023 UDP are forwarded to the IP of Ext B
— Ports 5067 TCP/UDP and 14024-14035 UDP are forwarded to the IP of Ext C
This also implies that the the phones/endpoints should have Static LAN IPs assigned to them.