Interconnecting Asterisk Servers with PJsip and OpenVPN

It’s been several years since we discussed interconnecting Asterisk® servers so today we want to do a version refresh using PJsip Trunking. We also want to show you how easy it is to secure the communications path by setting up the trunks using OpenVPN connections. When we’re finished, you’ll have a FREE way to call between sites using FreePBX® Outbound Routes. Because Incredible PBX comes preconfigured with all the components you’ll need, we’ll use that platform to further simplify the deployment. We’ll be interconnecting two Asterisk servers today, but you can use the same methodology to connect numerous sites.

To begin, you’ll want to get all of the sites configured with a virtual private network using OpenVPN. Our tutorial will walk you through the process. Keep in mind that all current releases of Incredible PBX are preconfigured to let you drop in your OpenVPN client credentials by naming them incrediblepbx.ovpn and copying the file into the /etc directory. Rebooting your server will bring up the virtual private network with a 10.8.0.x IP address.

If you remember yesteryear’s knuckle drill configuring SIP or IAX trunks for Asterisk connectivity, you’re in for a pleasant surprise using PJsip trunking with FreePBX. Using the GUI, create a new PJsip trunk for every site to which you want to establish a connection. A similar PJsip trunk must be created on the other site as well. If you’re just interconnecting two servers, then using the City locations for the Trunk Names will suffice. But, if there are more than two servers, specify unique names for each end of every PJsip connection, e.g.

NewYork1 <-> London1
NewYork2 <-> Washington1
NewYork3 <-> Miami1
London2 <-> Washington2
London3 <-> Miami2
Washington3 <-> Miami3

For today, we’ll interconnect a server in New York and London, but we’ll plan for the future and use London1 for the Trunk Name on the New York server and NewYork1 for the Trunk Name on the London server.

Let’s begin by configuring the London1 trunk on the New York server. After entering the London1 Trunk Name in the General tab, click on the pjsip Settings tab. In the General tab, leave the defaults in the first four fields. Then change the Registration field to None. For the SIP Server field, enter the OpenVPN IP address of the London server, e.g. 10.8.0.2. Because we’re using Incredible PBX, the PJsip port is 5061 so enter that in the SIP Server Port field. If you’re using a different flavor of FreePBX, enter the appropriate port number for PJsip on your platform. Next, click on the Advanced tab and enter the London server’s OpenVPN address in the Match (Permit) field, e.g. 10.8.0.2. In the Codecs tab, make note of the enabled codecs and make certain that the entries match on all of your servers. Click the Submit button to save your settings and then reload your dialplan.

Now let’s configure the NewYork1 trunk on the London server. After entering the NewYork1 Trunk Name in the General tab, click on the pjsip Settings tab. In the General tab, leave the defaults in the first four fields. Then change the Registration field to None. For the SIP Server field, enter the OpenVPN IP address of the New York server, e.g. 10.8.0.1. Because we’re using Incredible PBX, the PJsip port is 5061 so enter that in the SIP Server Port field. If you’re using a different flavor of FreePBX, enter the appropriate port number for PJsip on your platform. Next, click on the Advanced tab and enter the New York server’s OpenVPN address in the Match (Permit) field, e.g. 10.8.0.1. In the Codecs tab, make certain that the entries match those on your New York server. Click the Submit button to save your settings and then reload your dialplan. Here’s how it looks in the FreePBX GUI:

To keep things simple, let’s assume both your New York and London servers have extensions 701-705. To call an extension on the other server, we will simply dial 9 and then the 3-digit extension, e.g. dialing 9701 on the New York server will ring 701 on the London server and dialing 9701 on the London server will ring 701 on the New York server.

Create an Outbound Route on the New York server called London specifying London1 for the Trunk Sequence in the Route Settings tab. In the Dial Patterns tab, enter 9 in the Prefix field and XXX for the Match Pattern. Click Submit to save your settings and then reload dialplan.

Create an Outbound Route on the London server called New York specifying NewYork1 for the Trunk Sequence in the Route Settings tab. In the Dial Patterns tab, enter 9 in the Prefix field and XXX for the Match Pattern. Click Submit to save your settings and then reload dialplan.

If you’re interconnecting more than two sites, then you probably will want to designate a specific Prefix for every City so that users can travel between sites and use the same methodology to reach the same extensions from every location.

You can test things out using softphones by registering 701 to an extension in New York and another to the 701 extension in London. Now you can place secure and FREE calls between the sites by dialing 9701 from each softphone. Enjoy!

Originally published: Monday, May 2, 2022

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