TL;DR What technology should I use to translate an internal address ( to another internal address ( So that when I access the first I get redirected to the other?

Long Story I have a pbx box that I need to move from one location to another. The ip of the pbx box is and all the phones points to that address. When the pbx box is moved it will reside at As it is now the two different subnets are connected by a site-to-site connection which means that you can access from within no problem. (That is why I mentioned them earlier to both be internal)

My problem is that the move will take some time, and I will have to manually configure all the phones for the new location Hence I need to split this task up in two.

  • day one/ move server, nat(or what not) from address a to address b.
  • day two/ configure phones manually one by one, then remove natting(or what not)

In this way as I see it no one will ever be affected by the move

But my question is: is it a nat rule that i need to apply.

The setup: -> pfsense -> WAN(site-to-site) <-pfsense <-

  • Are you saying the phones will stay on the, but the PBX box alone will be moved to Is the site-to-site a VPN, MPLS, or similar? Or are both pfsense boxes on public WAN IPs? – jlehtinen Nov 14 '13 at 16:10
  • Yes, the phones will remain on It is a site-to-site vpn with public wan addresses. The site-to-site connection is configured and working well – JohanBot Nov 14 '13 at 16:26


pbx -> -> pfsense1 -> WAN(site-to-site) <-pfsense2 <- <- phones

Here's one way you could do this.


  • Add route in pfsense1 for using either pfsense2 WAN IP or VPN tunnel for gateway.
  • Add firewall rule in pfsense1 to allow necessary incoming ports FROM
  • Add route in pfsense2 for using either pfsense1 WAN IP or VPN tunnel for gateway.
  • Add firewall rule in pfsense2 to allow necessary incoming ports FROM


  • Change config on phones to look for PBX on
  • Change config on phones to use pfsense2 as default gateway.
  • Change pbx to ip
  • Change pbx default gateway to pfsense1.

Keep in mind that you need to know what ports the phones use, and you have to unblock those in the firewalls. Also keep in mind that depending on your hardware you may lose some functionality in the phones when working across VPN tunnels / WAN links. For example, 3com NBX's use multicast for time updates, status lights, and paging. Some hardware will simply not support multicast forwarding across a VPN channel - which means these features won't work on remote phones.

I would recommend setting up some kind of computer at the remote site, and then setting up the configs in the firewalls. Verify site-to-site routing/connectivity before continuing with the phones.

  • Thanks for the answer. You can say that the preparation step you mention is completed since the two sites are completely visible to each other. All traffic floats freely between the two sites. in your changeover it get a little confused. Because I can't change the phones to look for in first go. That has to come later. The phones can later be changed to point at, but for now I just want to "redirct" traffic to to Otherwise I don't understand – JohanBot Nov 14 '13 at 16:33
  • So you want to put the PBX box on the 192.168.2.x subnet, while it's still connected the network hosting the 192.168.1.x subnet? This might just be my opinion, but IMO scheduling a maintenance window and having a few hours of downtime would be less work than configuring (and later tearing down) the configuration you're suggesting. – jlehtinen Nov 14 '13 at 16:56

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