When I install Freepbx behind a router, I never forward any port (unless I have external phones). I know that it is usually not necessary (or recommended) to forward ports. Everything works fine but I noticed something strange in the firewall logs of the routers (PFSense and OPNSense). Whenever a call comes in, a whole bunch of incoming UDP connection from the voip provider between ports 10000 and 20000 are blocked by the firewall. The call works, the audio is good, everything is fine. I am just wondering why I see these connection from the providers (both voip.ms and babytel do the same thing).
Of course, forwarding ports 10000-20000 removes theses messages in the firewall logs, but I can’t help but wonder why these connection happen. I mean, if they we’re necessary, I wouldn’t have audio without forwarding.