[CentOS] how to create a local update server.

could someone please point me in the right direction for creating a local repository for centos updates.

Scenario: I have one centos server connected to the internet, it provides ntpd, httpd, and other services to both internal and external clients (only httpd is serving external clients).

the clients are connected to the first centos server and it functions as a NAT router for internet sharing purposes.

I'd like to create a local updates repository so that clients only need to check MY update server instead of the public ones. I'd like the option of just being a repository of the "update list" (the list of packages that are updated), and being a repository of the .rpm files themselves.