The repository of Nethserver is enabled by default, you need to install first a rpm. Each day a cron job will look after updates and will send an email to 'admin' in case of updates found (you need to install nethserver-directory).
yum install http://mirror.de-labrusse.fr/NethServer/6/noarch/nethserver-stephdl-1.0.4-3.ns6.noarch.rpm
or for NS7
yum install http://mirror.de-labrusse.fr/NethServer/7/x86_64/nethserver-stephdl-1.0.4-3.ns7.sdl.noarch.rpm
Then you have to enable it first if you want to install rpms, for example
yum install nethserver-password --enablerepo=stephdl
and for update
yum update --enablerepo=stephdl
Here my available rpm