To make clients fetch their packages off the mirror, you need to know its IP number (or its hostname).
On a freshly installed Ubuntu Precise, replace the hostname of the repository server with the hostname or IP number of the mirror.
E.g. if /etc/apt/sources.list
looks like:
###### Ubuntu Main Repos deb http://ce.archive.ubuntu.com/ubuntu/ precise main restricted universe multiverse ###### Ubuntu Update Repos deb http://ce.archive.ubuntu.com/ubuntu/ precise-security main restricted universe multiverse
and your mirror is at 10.0.25.1, then you want to do:
user@clientPC:$ sudo sed -i.netmirror 's%ce\.archive\.ubuntu\.com%10.0.25.1%g' /etc/apt/sources.list