Get the external IP of your system - useful if you have a dynamic ip…

curl -s checkip.dyndns.org|sed -e 's/.*Current IP Address: //' -e 's/<.*$//'

Find the IP address of all the active interfaces.

ifconfig | egrep -o '^[a-z0-9]{1,12}|inet addr:[0-9.]+'

DDClient is a tool that lets you auto update your ip with services like dyndns.org. This is how you install it…

Download http://sourceforge.net/project/showfiles.php?group_id=116817

Extract the downloaded file
Open that folder in a terminal and run these commands as root to install the software…

cp ddclient /usr/sbin/
mkdir /etc/ddclient
cp sample-etc_ddclient.conf /etc/ddclient/ddclient.conf
vi /etc/ddclient/ddclient.conf

Now edid the config file as you need.