try this, you will install the last version of ddclient (3.8.3) and a rpm modified for the correct url of zoneedit (dynamic.zoneedit.com)
yum install http://mirror.de-labrusse.fr/nethserver/ddclient/nethserver-ddclient-1.0.1-4.ns6.sdl.noarch.rpm http://mirror.de-labrusse.fr/nethserver/ddclient/ddclient-3.8.3-1.ns6.sdl.noarch.rpm