NATTING in Ubuntu Server

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http://askubuntu.com – My Server has two NIC, One is connected to the Internet Service provider with dhcp ip (dynamically change) given by ISP and other NIC is connected with local Switch with IP. Now I want to set up network with such that computers connected with LAN can connect Internet through server. Server will be work as a router. How should I make such configuration that All traffic passed by NIC 2 within a single IP and ported at IP address of NIC 1 which is Dynamically given by My ISP? Thanks in advance. (HowTos)