Using MonMotha's firewall script to build safe Internet sharing with Debian GNU/Linux: HOWTO Version
IP Masquerading is a type of network address translation (NAT) in the Linux kernel which allows packets (chunks of formatted data) from an internal machine to appear to be coming from the public interface of the firewall. This allows machines on the local network to assume the address of the firewall when communicating on the internet, thereby making them "hidden" from attackers."
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