Load balancing traffic with Kamailio v4.1

Load balancing traffic with Kamailio

Note: We assume you have Asterisk/Freeswitch setup to handle inbound traffic from Kamailio

In part 3 of our Kamailio series we will explain how to load balance calls from users between several different media servers. For this part in the series we will use the “dispatcher” module. The dispatcher module provides us with several different ways to load balance calls from round-robin to weight based routing.

Getting Started

For this tutorial, you’ll only need one thing besides Kamailio and that is a list of media servers. If you don’t have any media servers, we recommend using Freeswitch and/or Asterisk.

Configuring Kamailio

By default, Kamailio does not load the dispatcher module or any of the modules respective settings. Let’s start with loading the module into Kamailio. Open up your kamailio configuration file (/etc/kamailio/kamailio.cfg), find the load modules section and add the following line:

 loadmodule “dispatcher.so”

Scroll down further in the file until you locate the module parameters section. Go the bottom of that list and add the following:

modparam("dispatcher", "db_url", "mysql://kamailioro:kamailioro@localhost/kamailio")
modparam("dispatcher", "table_name", "dispatcher")
modparam("dispatcher", "flags", 2)
modparam("dispatcher", "dst_avp", "$avp(AVP_DST)")
modparam("dispatcher", "grp_avp", "$avp(AVP_GRP)")
modparam("dispatcher", "cnt_avp", "$avp(AVP_CNT)")

Save the file and restart Kamailio to make sure there are no errors. You can restart kamailio with:

# kamctl restart

If that didn’t work, go back and make sure you have everything entered properly. Once it’s running with no problem open back up the configuration file and proceed to the “request_route” section. Comment out the following line by appending a “#” pound symbol to the front of it.


Right below add the following line:


It’s time to add the actual code that will do the dispatching. Go to the code block below “route[RELAY]” and add the following:

  # round robin dispatching on gateways group '1'
  if(!ds_select_dst("1", "4"))
    send_reply("404", "No destination");
  xlog(“ —— DISPATCH: going to <$ru> via <$du>n");

In the above code, we chose to use the round-robin algorithm for routing calls. Basically, our calls will cycle between the media servers we chose to setup. If we have 2 media servers setup our calls will process like so, call 1 will go out of MS1, call 2 out of MS2, call 3 out of MS1 and so on.

With the dispatching code in place, we’ll need to add the actual destinations into the Kamailio database. Login to your MySQL database and execute the following commands. You can replace the destination and description with your media servers.

mysql> INSERT into dispatcher (setid, destination, flags, priority, attrs, description) VALUES (1, “sip:asterisk.example.com:5060”, 0, 0, "", "Endpoint: Asterisk Media Server");
mysql> INSERT into dispatcher (setid, destination, flags, priority, attrs, description) VALUES (1, “sip:freeswitch.example.net:5060”, 0, 0, "", "Endpoint: Freeswitch Media server");

With that completed, we’ll need to reload Kamailio. Since we haven’t restarted Kamailio since adding the dispatch route let’s just restart Kamailio using the same command as before. However, if you restarted Kamailio since adding the dispatch route you can just use the following command to reload the dispatcher info.

# kamctl dispatcher reload

Now that the routes are loaded into Kamailio, all you’ll need to do is push some calls through to Kamailio and they will be routed in a round-robin fashion like we stated above.


  • Dispatcher Modules Documentation – http://kamailio.org/docs/modules/4.1.x/modules/dispatcher.html