wget http://cdn.dyndns.com/ddclient.tar.gz
tar -xzvf ddclient.tar.gz
cd ddclient-3.7.3/
mkdir /etc/ddclient
mkdir /var/cache/ddclient
cp ddclient /usr/local/sbin
cp sample-etc_ddclient.conf /etc/ddclient/ddclient.conf
cp sample-etc_rc.d_init.d_ddclient /etc/rc.d/init.d/ddclient
chkconfig --add ddclient
cd ..
rm -rf ddclient-3.7.3/

Now edit the /etc/ddclient/ddclient.conf file:

vim /etc/ddclient/ddclient.conf

so that it contains something like:

use=web
login=yourdndnslogin
password=yourdyndnspassword
server=members.dyndns.org,            \
protocol=dyndns2                      \
yourhost.dyndns.domain

Now start the ddclient daemon:

/etc/init.d/ddclient start

You can check status and troubleshoot using:

/etc/init.d/ddclient status
/etc/init.d/ddclient stop

tail /var/log/messages