NAT (Network Address Translation) works by translating private IP addresses used within a private network to a public IP address before traffic is routed to the internet. This allows multiple devices on a private network to share a single public IP address. NAT is typically implemented on a router, which acts as an intermediary between the private network and the public network (like the internet).
Here’s a breakdown of the process:
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Private Network Communication: Devices within a private network use private IP addresses (e.g., 192.168.1.x). These addresses are not routable on the public internet.
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Data Transmission: When a device on the private network needs to communicate with a device on the public network, it sends data (packets) to the router.
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Router Interception: The router, which is where NAT is implemented, intercepts this data.
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Address Translation: The router replaces the source IP address (the private IP address of the sending device) with its own public IP address. This is the core function of NAT. The router also usually changes the source port number and stores this mapping in a NAT table.
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Data Forwarding: The router then sends the modified data packet, now bearing its public IP address and the new source port number, to the destination device on the public network.
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Return Traffic: When the destination device responds, it sends data back to the router's public IP address and the specific source port number that the router previously chose.
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Reverse Translation: The router uses the NAT table to determine which private IP address and original source port number the return traffic is intended for. It replaces the destination IP address (the router's public IP address) with the original private IP address, and the destination port number with the original source port number.
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Delivery to Private Device: Finally, the router forwards the data to the correct device on the private network.
In essence, NAT hides the internal network's structure and IP addresses from the outside world, enhancing security and allowing efficient use of limited public IP addresses.
