What Is IP Masquerading?

IP Masquerade is a specific form of Network Address Translation (NAT) which allows internally connected computers that do not have registered Internet IP addresses to communicate to the Internet via the Linux server’s Internet IP address. It lets you use a single Internet-connected computer running Linux with a real IP address as a gateway for non-connected machines with “fake” IP addresses. The Linux box with a real address handles mapping packets from your intranet out to the Internet, and when responses come back, it maps them back to your intranet. This lets you browse the web and use other Internet functions from multiple machines without having a special network setup from your ISP.

IP Masquerade is a networking function in Linux similar to the one-to-many NAT (Network Address Translation) servers found in many commercial firewalls and network routers. For example, if a Linux host is connected to the Internet via PPP, Ethernet, etc., the IP Masquerade feature allows other “internal” computers connected to this Linux box (via PPP, Ethernet, etc.) to also reach the Internet as well. Linux IP Masquerading allows for this functionality even though these internal machines don’t have an officially assigned IP address. IP masquerading is different from NAT. While IP masquerading implements a specific many-to-one NAT, IP NAT allows complex many-to-many translations. For static real IP address we use NAT, while for dynamic real IP address (via PPP) we use IP masquerading.