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The Figure illustrates NAT operation when NAT is used to map one virtual host to several real hosts. The steps in the following list correspond to the numbered NAT operation steps shown in the Figure:
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User on host B (172.20.7.3) opens a TCP connection to the virtual host at 10.1.1.127.
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The router receives the connection request and creates a new translation allocating the next real host (10.1.1.1) for the inside local IP address.
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The router replaces the destination address with the selected real host address, and then forwards the
packet.
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Host 10.1.1.1 receives the packet and responds.
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The router receives the packet and performs a NAT table lookup using the inside local address and port number, and using the outside address and port number as the key. The router then translates the source address to the address of the virtual host and forwards the packet.
The next connection request causes the router to allocate 10.1.1.2 for the inside local address.
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