New On Prem Install, Mult WAN IPs, How to set/change FQDN IP

[Paul_Mule]

New install, v20 Ent, have range of static IPs, xxx.xxx.xxx.138 thru 145 and want to use an IP other than WAN ip of router, .138. How can I do this? TIA

Configured network manually

• IP: 10.100.50.200
• Gateway: 10.100.50.1
• Name Server: 8.8.8.8

 

[positron]

You will have to look at settings for your firewall/router, usually something like "one-to-one NAT" to map a specific static IP address to a specific internal IP address so it will be reserved and used exclusively for your 3CX system.

 

[Paul_Mule]

Yes, one to one NAT has been setup. Let me clarify...

Public/WAN IP RANGE: xxx.xxx.xxx.138 thru 145.
Public/WAN IP used by router: xxx.xxx.xxx.138
Public/WAN IP used for 3CX: xxx.xxx.xxx.140 -> 1 to 1 NAT to 10.100.50.200 with applicable ports

3CX FQDN: mypbxname.3cx.us ->currently set to ip xxx.xxx.xxx.138

I need to change the 3CX FQDN (mypbxname.3cx.us) to xxx.xxx.xxx.140. How is this done?

 

[positron]

Admin, Advanced, Network; Change static IP.

There used to be an issue in the past (I don't know if it's still an issue) where you couldn't change the static IP or changing the static IP would not update the FQDN. If that's still an issue, the workaround for that was to change from static IP to dynamic IP, confirm the IP is detected, then change back to static IP with the new/correct IP.

 

[Paul_Mule]

Thank you for your replies. My dilemma is, the business router is configured and using all 8 static WAN ips. So the PBX traffic is isolated on a separate IP from the router ip. If the router ip is temporarily changed from xxx.xxx.xxx.138 to xxx.xxx.xxx.140, and the FQDN updates to 140, it will just go back to xxx.xxx.xxx.138 after original router settings are restored, correct?

3CX controls the FQDN. Is there a process to get this changed? Since this a new install, I can rebuild if needed. What revealed this problem was after loading the config file, you're prompted with a link to "Click here to set your password". Since the ip for that link is the router and not the pbx ip, the 1 to 1 NAT doesn't work.

 

[positron]

Thank you for your replies. My dilemma is, the business router is configured and using all 8 static WAN ips. So the PBX traffic is isolated on a separate IP from the router ip. If the router ip is temporarily changed from xxx.xxx.xxx.138 to xxx.xxx.xxx.140, and the FQDN updates to 140, it will just go back to xxx.xxx.xxx.138 after original router settings are restored, correct?

3CX controls the FQDN. Is there a process to get this changed? Since this a new install, I can rebuild if needed. What revealed this problem was after loading the config file, you're prompted with a link to "Click here to set your password". Since the ip for that link is the router and not the pbx ip, the 1 to 1 NAT doesn't work.

You should not need to change the public IP assigned to the router/firewall, only the NAT/routing rules associated with the IP assigned for 3CX.

You may not have 1-to-1 NAT configured properly. If working, it would translate between your x.x.x.140 public IP and your internal 3CX private IP in both directions. This is usually not done using port forwarding rules (although you may have firewall rules which restrict the incoming ports allowed), but by a direct IP-IP mapping.

If you change 3CX to use a dynamic IP and it detects .138 instead of .140, then your router configuration is the problem. You would need to contact someone familiar with your router/firewall hardware to advise on 1-to-1 NAT setup.

The 3CX system will automatically update your 3CX FQDN with the assigned IP address, whether static or dynamic.

 

[Paul_Mule]

So if I understand correctly, regardless of my public IP assigned to the router, if 1 to 1 NAT is setup properly, the FQDN will auto update to the WAN address assigned to the 3CX PBX. Does the 3CX server 'phone home' to communicate the public ip it is using?

Until this is working and I set my password, will I not be able, from the LAN side using LAN IP, to access the 3CX PBX login page? Currently, I cannot.

 

[positron]

So if I understand correctly, regardless of my public IP assigned to the router, if 1 to 1 NAT is setup properly, the FQDN will auto update to the WAN address assigned to the 3CX PBX. Does the 3CX server 'phone home' to communicate the public ip it is using?

Until this is working and I set my password, will I not be able, from the LAN side, to access the 3CX PBX login page? Currently, I cannot.

The 3CX server will update your 3CX-assigned FQDN to resolve to the static IP address assigned in the 3CX server settings, regardless of whether your router/firewall is translating correctly or not. Once set, it will never change unless you change the static IP address setting in 3CX. If your router/firewall is not assigning that static IP to packets originating from the 3CX server, you will have problems.

If you are trying to access the system from an internal LAN, you need one of the following:

• Split DNS, which allows internal systems querying your 3CX FQDN to resolve to the internal LAN IP
• Hairpin NAT, which allows the router/firewall to take traffic originating from the LAN destined for the assigned 3CX public IP and redirect it back to the internal private IP
• an entry in the local "hosts" file of the computer/device trying to access the 3CX server, resolving the 3CX FQDN to the internal IP of the server

If you cannot access the 3CX server from the local LAN because of a configuration issue and are temporarily prevented from setting up split DNS or hairpin NAT, you can temporarily add the "hosts" entry so your computer can correctly resolve the FQDN and establish a HTTPS session.

 

[Paul_Mule]

Understood.
https://www.3cx.com/docs/creating-fqdn-split-dns/
split dns has been setup.

I was trying to specify lan ip:5015 and was not working until I dropped the port #. The FQDN from the lan is now displaying the login. I'll get to work on the FW NAT now. Thank you Jody for your help.

 

[Paul_Mule]

Final note. For this scenario multiple static WAN IPs where the router ip IS NOT the WAN IP to be used for the On-Prem 3CX Version 20 pbx, go here Admin / Advanced / Network / External IP configuration and set the desired Static Public IP.. This will update the FQDN from 3CX. Positron already explained this but wanted to clarify, this currently works as it may not have in the past.