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Does a firewall need two static IPs for port forwarding?

I am using a Cisco PIX Version 6.3(5) firewall and I have only one static IP. My supporters tell me that it takes two static IPs to do port forwarding in a firewall. Is it true that I require two static IPs? Please explain, if this is so.

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Port forwarding is the act of forwarding a network port from one network node to another. This technique can allow an external user to reach a port on a private IP address (inside a LAN) from the outside via a NAT-enabled router.

Routers are configured with two interfaces: One is your WAN interface that connects to the Internet and is configured with a Public IP address ( provided by your ISP. The second is an internal (LAN) network interface which is configured with your local internal (LAN) static IP address (

This was first published in October 2007

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