In our last post we covered the theory behind ENUM and its use, and in this post we’ll cover setting up Kamailio to query an ENUM server.
Before we start, if you’re not familiar with ENUM, check out my primer on the topic here, and then for more in-depth info check out this post on configuring an ENUM server in Bind and the ways records can be configured,
So once we’ve got an ENUM server configured and confirmed we can query it and get the results we want using Dig, we can configure Kamailio.
But before we get to the Kamailio side, a word on how Kamailio handles DNS,
Kamailio doesn’t have the ability to set a DNS server, instead it uses the system DNS server details,
This means your system will need to use the DNS server we want to query for ENUM for all DNS traffic, not just for Kamailio. This means you may need to setup Recursion to still be able to query DNS records for the outside world.
To add support to Kamailio, we’ll need to load the enum module (enum.so),
In terms of parameters, all we’ll set is the doman_suffix, which is, as it sounds, the domain suffix used in the DNS queries. If you’re using a different domain for your ENUM it’d need to be reflected here.
modparam("enum", "domain_suffix", "e164.arpa.")
Next up inside our minimalist dialplan we’ll just add enum_query(); to query the SIP URI,
if(is_method("INVITE")){
enum_query();
xlog("Ran ENUM query");
xlog("To URI $tU");
forward();
}
Obviously in production you’d want to add more sanity checks and error handling, but with this, sending a SIP INVITE to Kamailio with an E.164 number in the SIP URI user part, will lead to an ENUM query resolving this, and routing the traffic to it,
An example PCAP above, showing a call to +61355500912, the resulting ENUM query and routing to server1.enum.nickvsnetworking.com,
By using Kamailio’s transaction module ™ as a stateful proxy, we can run queries again if one were to fail,