HannibalWiki

Many people communicate on a day to day basis using tools like Google Hangouts, Skype, Whatsapp and what have you. What do most of these tools have in common? Well, though they're meant to communicate, they're only open as long as you communicate with other people who make use of the same proprietary solution, i.e. they don't support open standards like XMPP or SIP. Google used to support XMPP in Google Talk, however XMPP isn't supported anymore since they moved to the current Google Hangouts.

Anyway, the good news is: we can do it ourselves…, oh, Yes We Can

Let's build a solution that allows us to chat, transfer files, phone and videophone without having to use a proprietary tool and without having to get an additional contract with a service provider or telco.

We'll use the ejabberd software as backend XMPP-solution as it is an open source, scalable, robust and secure solution that is available through the default Debian Wheezy software repository. In addition to the server we chose to install Jitsi on the clients as Jitsi is an open source XMPP-client that is full featured. Also, Jitsi packages are available for many desktop platforms and packages for mobile devices are being developed.

First we have to plan which domain we'll use for our XMPP-server. Assume we choose the domain 'example.com' to be configured on our XMPP-server named 'jabber', then the identity of our XMPP-users, which is called 'JID', would become user1@example.com, user2@example.com etc. Just like e-mail, that is. Also just like e-mail, we have to tell DNS how the XMPP-clients and external XMPP-servers can reach our server. In order to prepare DNS, add SRV-records like so to the 'example.com' domain (assuming an A-record for 'jabber.example.com' already exists):

_xmpp-client._tcp 900 IN SRV 5 0 5222 jabber.example.com.
_xmpp-server._tcp 900 IN SRV 5 0 5269 jabber.example.com.
_jabber._tcp      900 IN SRV 5 0 5269 jabber.example.com.

You can check your new entries like so:

dig -t srv _xmpp-client._tcp.example.com

After installation of the ejabberd server, several TCP-ports will be opened up on the server. It's advisable to only allow external traffic to and from the following ports (assuming you don't change the default values):

• port 4369 # don't allow external access to epmd, though we need it locally for the ejabberdctl tool
• port 5222 # allow XMPP-client traffic
• port 5269 # allow XMPP-server traffic
• port 5280 # don't allow HTTP admin-interface on the wild wide web
• port 7777 # allow file transfer via mod_proxy65 (SOCKS5 bytestreams)

Installation of the ejabberd server is rather easy as a pre-compiled software package is available through the default Debian Wheezy software repository. So, just install the server:

apt-get install ejabberd

During the installation process a basic setup is stored in the ejabberd database (this is a mnesia-database as ejabberd is written in Erlang). Let's customize the hewly created ejabberd configuration. The main configuration file is /etc/ejabberd/ejabberd.cfg When you take a look at this file you'll notice that comments start with '% %' characters, and lines finish with a ‘.’ character. Ok, first we have to tell ejabberd that we want to override the initial configuration. Uncomment the 'override_acls.'-directive:

...
%%
%% Remove the Access Control Lists before new ones are added.
%%
override_acls.
...

Then configure the admin-user:

...
%% Admin user
{acl, admin, {user, "zebigboss", "example.com"}}.
...

Check the hostname of the server.

...
%% Hostname
{hosts, ["example.com"]}.
...

If you want to serve more domains, you can configure a hosts-directive like so:

...
%% hosts: Domains served by ejabberd.
%% You can define one or several, for example:
{hosts, ["example.net", "example.com", "example.org"]}.
...

Now let's adjust the default listener so that ejabberd also supports IPv6. In addition, we want TLS to be required for all of the client connections. The self-signed certificate '/etc/ejabberd/ejabberd.pem' has been created by debconf. Of course you could use your own certificate instead.

...
{listen,
 [
  {5222, ejabberd_c2s, [
                        inet6,
                        {access, c2s},
                        {shaper, c2s_shaper},
                        {max_stanza_size, 65536},
                        %%zlib,
                        starttls, starttls_required, {certfile, "/etc/ejabberd/ejabberd.pem"}
                       ]},
...

And if you change the name/location of the certificate, don't forget to check the server to server-directive around line numer 206 of the configuration file:

...
%%
%% s2s_certfile: Specify a certificate file.
%%
{s2s_certfile, "/etc/ejabberd/ejabberd.pem"}.
...

Fine, now we're done. Let's restart the server and check if things are OK. Ejabberd logfiles are stored in /var/log/ejabberd

service ejabberd restart

Check if the listeners have come up:

netstat -nalp |egrep '5222|5269'