This tutorial shows how to create a YUM repository which you can use on your own private network. You may want this if you do not want your production servers to reach on the Internet thus keeping them protected. These servers will get their RPM packages by a server that holds the always up to date RPM packages. This is called the repository server and it will need access to the Internet in order to get the latest RPM packages.
1) Find an official CentOS site that supports RSYNC. List of Links here.
2) Have a spare server to use as your Repo server. This server will need to have Apache installed.
3) Enter an DNS entry for the local web site you will create that will host the RPM packages.
4) Setup yum on your servers to get the new packages from your Repo Server.