Provisioning failing if on-premise server has certain IP

[testing]

Hello,
We have a block of public IPs we have been treating as private IPs closed off by a firewall (Don't ask why this is just how it has always been long before me). If I set up the on-premise server with an IP on this range and phones also in this block the phones will not show up in the management console and all provisioning attempts fail. However when I set up the on-premise server on our super-scoped overflow dchp which IS in the private IP range (192.168.x.x) and set the phones to the same IP range, the phones DO display in the console and provisioning works without fail. Through process of elimination I have narrowed it down to this being the only difference between the two servers. Is the fact that in the first scenario the IP being used is technically a public IP causing this issue? Any suggestions/explanations are greatly appreciated.

 

[YiannisH_3CX]

Hello @testing

Yes the public IPs are causing your issue. The PBX knows that the registration is coming from a public IP as that IP is not part of the RFC1918 which details local IPs and treats the phone as a remote device.
To register a phone that way you will need to treat the phone as a remote device and disable the " Disallow use of extension outside the LAN (Remote extensions using Direct SIP or STUN will be blocked) " option which is in the options tab of your extension settings. That of course decreases security unnecessarily and is not recommended. You might also face other issues down the line. I would recommend setting the PBX in a VLAN with a true public ip and add the phones to that vlan as well.