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When I visit some Web sites that display your IP address, it correctly identifies mine and not that

When I visit some Web sites that display your IP address, it correctly identifies mine and not that of my router. Why is this when I am operating in NAT (gateway) mode?
This is definitely not a wireless questions, but I'll happily give you a hand.

For those out there unfamilar with NAT, NAT (Network Address Translation) is a protocol that allows machines operating in one subnet (eg subnet mask to be converted to a public address so that people on the

If a machine with a private IP address (eg. was connected directly to the internet it would not function correctly. The way the communication works is that information sent from the private IP address would reach its destination however when the destination attempted to reply to the private IP it would send the packet to one of the Internet Core Routers. Internet Core Routers are responsible for keeping location/routing information for all known IP ranges however they are also away that is a private IP address. The packet would then be dropped as no legitimate route exists for private IP addresses.

As you're using NAT, when you use the Internet your router switches your private IP address for its public IP address as traffic passes through it. When you access the web page the web page sees a source IP address of your router (as its swapped the addresses) and so the web page tells you that your IP address is really the IP address of the router. The beautiful protocol means that you can put almost any IP address behind your router and not intefer with the settings as dictated by your ISP and at the same time your internet connection will continue to function no matter how you design your internal network.

This was last published in May 2004

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