IPtables Block and Allow

[Yuzz]

Hi all,

I'm new here and i would like to seek some help from you all regarding on iptables simple rules. Recently i setup one linunx server and want to be firewall using iptables.Here is my setup =  eth1(private network) and eth0(public network). Here is my question

1) How do i block access private network to internet port 80 and allow internally access port 80.
2) How do i force all private network using proxy to access internet using 3128

Hope somebody will help give some guide. thanks
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