I have 3CX installed and running behind a Linksys router that has a staic public address. I had port forwarding setup as directed in https://www.3cx.com/docs/manual/firewall-router-configuration/, and everything worked. I'm using CallCentric for my SIP account, and I have STUN turned off. Today I turned off the port forwarding, and everything still works fine. I even unplugged the Linksys router for about 30 seconds and plugged it back in. How is it working without the port forwarding?