Remote site SIP trunks over VPN

Hello guys,

I have a simple installation between my two offices and I’m using Freepbx 13 with Asterisk without any problem. My Freepbx server is running under Centos 6.3 and its located in my first office. I have already registered my first office’s land lines as SIP trunks there (from my provider into my freepbx) and everything is working fine. Using a VPN, I am also able to use all my telephony and stations on both offices. Please check the network diagram i made for this reason:

As you can see from my diagram, on my Office 2, there is a general purpose linux server there, but its not related with telephony. Over there, I have one more land line (as a SIP trunk) and I want to register it in my Freepbx as well. But… I cannot due to a different ISP on my Office 2. Unfortunately both of my ISP’s (ISP1 and ISP2) trunks need to be run under their own internet provider. And if you try to register Trunk3 on a system located under ISP1 it rejected.

So, the only solution I can think at the moment is to install another Freepbx server (or even a Raspberry PI 3) in my Office 2 to carry ISP2’s trunks and then to connect those two Freepbx together through my VPN.

But Instead of installing a new server there, is there any other “configurable” solution that I can use on my current Freepbx and have a remote SIP trunk registered at my other end instead of locally??? Or… maybe a kind of setting an internet gateway specifically on a sip trunk?? or… whatever :thinking:

BTW, I tried to use “socat” or iptables on my Debian server to redirect my ISP sip over my VPN but finally does not work.

Anyway, thanks for your time guys

I find the setup a little confusing. When you say trunk, what do you really mean? Specially on your 2nd office, where you don’t have a PBX, how is that trunk terminated? Or are you referring to an ATA with FXS ports?

Hello arielgrin,

As you can see, I have there one (or more anyway) Cisco SPA525G2, so I don’t really need any ATA with FXS for termination. I can directly register my trunk on one of Cisco’s SIP phone lines (has 5 anyway). But anyway the problem is not the termination in Office 2…


Strictly, if you have a Cisco Phone, you don’t really have a trunk. You have what can be considered as an IP equivalent of a traditional line. You can’t connect that line as a trunk, you can think that phone as being an extension of your provider’s pbx that happens to have a DID. Unless your provider allows you to register that extension on your own PBX, which they probably won’t, there is no way to use that phone from the other site.

Unless it is a real trunk, but that would be really strange, as a trunk is not supposed to be configured directly on a phone.

My dear arielgrim, please you do not need to explain to me what is really a trunk and if it supposed or not to be configured directly on a Cisco phone or not because all this is waste of time for all of us my friend. And my main question was out of this topic. As you clearly can see in my diagram, my SIP Trunk3 is not connected or terminated to anywhere and just still exists in my subscription in my Office2 site. As I told you, whenever I need to terminate it through an ATA FXS or a directly on a Cisco phone, it is the easiest thing in this world for almost everybody here. My question is located on my Office 1 and its clear. How and If can I register this trunk through my VPN using other end’s ISP connection. And of course I am asking If somebody has any idea how to do it without installing a new PBX locally (Office 2)…

Anyway thank you for your time and for your notice regarding my unconnected “Trunk 3” on my diagram.

Sorry for my confusion, I was not implying you needed the explanation, I was just trying to understand your scenario to better help you, but as I saw an icon of a phone, I understood it was connected to a phone.
I’m thinking of a VPN connecting the two sites and a SIP proxy (Kamailio for example) on your 2nd site so you can connect trunk3 to pbx on 1st site. That means you need another server on 2nd site dedicated to Kamailio, but if you don’t want to install a second pbx, probably you won’t want to install Kamailio

My friend arielgrin,

What you are suggesting is the same with what I clearly said from the beginning… Please read my post:

But please, think that this topic has already six replies till now saying basically what I said from the beginning!!! And as you know, this is the safest way for somebody who “may” have a solution or some knowledge about the problem, to get bored and finally not to reply due to waste of his time reading and reading about the same.

I really appreciate your readiness to help or make everything even more clear, but please lets see if someone has any other “idea” about my issue…

When you say that you already tried to register trunk3 from 1st site and it got rejected, I assume you tried to register the trunk using the VPN as a gateway to the 2nd site . If that is the case, then no, there is no way of registering that trunk without using a device in between, be it a proxy, an SBC or another FreePBX.

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