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Old 9th November 2016
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jggimi jggimi is offline
More noise than signal
 
Join Date: May 2008
Location: USA
Posts: 6,908
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Quote:
Originally Posted by shep View Post
Am I running NAT ... ?
I don't know, because I don't have a clear understanding of your network. But neither do you, so I will guess you are not using NAT yourself -- other than in your ISP connected router.

What is NAT? Network Address Translation. NAT is only performed by a router, and it is possible (but unlikely) your local network may have routers other than the Netis device. Your Netis device is a router, and it performs NAT. But any of your computers with 2 or more NICs could also act as a router.

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To understand NAT, you must first understand what a router is, and what one does. Simply described, a router is a computer with at least two NICs, which routes, or forwards packets from one network to another.

Here is an example of two TCP/IP networks, each with 3 computers, and with with a router in between. The router has two NICs, with an address on both networks.

Network 1: 192.0.2.0/24
Computer 1A: 192.0.2.1 Computer 1B: 192.0.2.2 Computer 1C: 192.0.2.3

Network 2: 198.51.100.0/24
Computer 2A: 198.51.100.1 Computer 2B: 198.51.100.2 Computer 2C: 198.51.100.3

Our router that interconnects these networks has two NICs: 192.0.2.99, and 198.51.100.21.

Diagrammed:
{192.0.2/24} - {192.0.2.99} [Router] {198.51.100.21}- {198.51.100/24}

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Without NAT, each of the six computers is identified by its own IP address. Communication between Computer 1A and 2C require that they each know the other's IP address. (Also, that they know there is a router between them.)

But with NAT, the router will translate packets, as if they originated on the router alone. If we use NAT with Network 1, all communication with Network 2 appear to have originated in the router itself. All devices on Network 1 will share a single address: 198.51.100.21. Network 1 is now a "private" network, unseen and unknown by Network 2. If Computer 1A sends a packet to computer 2C, the router in between will change the packet, and translate the origin address. The router will also keep track of the communication, so that it knows where to forward any replies, also translating the address back in the returning packet.

The most common place to find routers that do NAT (or sometimes, "NAT Routers") is in a home or small office connected to the Internet. There may be multiple devices on a private network, but all sharing a single IP address on the Internet. They do this with a single, external facing NAT router.

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Diagram your local network. It will help you to understand how the various bits all fit together.

Last edited by jggimi; 9th November 2016 at 01:13 AM. Reason: clarity, typos
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