While I am finding many a discussion on how to setup a chan_sip trunk on a fail over WAN connection properly I am unable to find anything definitive for PJSIP trunks, so I am hoping to find out here what the proper way is to get a PJSIP trunk configured.
Our setup is as follows: A single FreePBX box behind a firewall/router that has two connections with two different external static IP addresses configured on it. All traffic normally goes over the primary connection, however if the primary connection goes down the secondary takes over right away. Both these connections have different outside static IP addresses.
All our extensions are on the same internal network as the PBX (none connect to it over the external IP addresses). We are connecting to our SIP trunk provider using PJSIP trunks (NOT chan_sip, we don’t use chan_sip for anything on this particular setup).
We also have the System Admin Pro module purchased with DDNS enabled.
Given that the General SIP settings page doesn’t take a FQDN for the External IP address field I am not sure how to properly configure this so that in case of our primary internet connection failure once the IP address we are using to get online has changed to our secondary, external calls still work properly without us having to manually change the External IP address under the General SIP settings.