[CentOS] Yum upgrade inside firewall

We have several CENTOS 4.X which inside Firewall.  I can NOT run "yum" inside firewall to upgrade O.S. to new release.
 
Does there has way I can download all RPM to otherside firewall server then transfer those files into servers inside firewall and upgrade.
 
Anyone have procedure dicuments or website can be reference?
 
Thanks.


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