SIP trunks and backup Internet connection

I have a site running FreePBX distro the site uses SIP trunks. The site has two internet connections from two different providers (Comcast and At&T DSL) and both connections have static IP addresses.

I was having problems with calls drops when I had the system configured with NAT going through the Sonic Wall firewall. We could not resolve the issue so I moved to a dual homes setup. I have the FreePBX system dual homed with a external interface for internet connectivity with a static public for the SIP trunks and an internal interface for the phones. This resolved the call drop issues.

The customer is wanting to use the DSL as a backup if the primary Internet goes down and this is where I need some help. how can I make this work? I can put a third NIC into the system and configure it with a static address from the DSL provider. I guess the problem is how to setup FreePBX to know that its’ external IP has changed if the primary Internet drops and the secondary DSL connection is used.

I set this up at my office and it works great. The website is:

It has documentation on how to set it up.


1st of all, if you are on a call and the Internet connection that call was going thru drops then the call is going to drop. The difference is when you have a failover is that you can reestablish the call immediately. No backup internet and you be down… unless you have POTS too :slight_smile:

So, to solve this I found two ways that work for me.

  1. For a dual WAN a Peplink B20 does a real good job of managing connectivity to a single LAN network. I am suggesting that you do not overcomplicate the PBX to achieve Internet failover, but put that feature at the head end of the network. That way all LAN devices can benefit as well. And yes I am suggesting that the B20 will do a better job then sonicwall and the issue you were having with call drops would not exist to begin with… so you could keep the PBX on the LAN with the phones and declutter the setup further.


  1. Use a Vyatta appliance to manage the dual WAN. I won’t go into detail as a) option 1 is roughly $300US and sorta easy to setup and b) an entry level Vyatta is $795 and you would likely have a steeper learning curve to make it work. I know I did.