NAT address translation process

The NAT address translation process is as follows: 1. The client sends packets to the computer running the NAT service. 2. The NAT host converts the source port number and source private IP address in the data packet to its own port number and public IP address, and then sends the data packet to the target host of the external network, at the same time, a trace information is recorded in the address translation image table to send response information to the client. 3. Send a message to the NAT host from the external network. 4. The NAT host converts the port number and public IP address of the received data packet to the port number of the target host and the dedicated IP address of the target host in the internal network based on the record in the image table, and forwards it to the target host. For example, an Intranet machine (192.168.0.5) accesses the target host (220.181.28.42). 1. The client sends data packets to the destination host 220.181.28.42 destination port 80 source host 192.168.0.5 (private IP address of the Intranet) source port 1025 (random access) 2. IP address translation destination host 220.181.28.42 destination port 80 source host 218.22.192.21 (Public IP address of the NAT server) source port 5000 (open randomly) 3. Record the image 192.168.0.5 tcp 1025 ----- 218.22.192.21 tcp 5000 4. The external network host sends a response to the NAT host. The destination host 218.22.192.21 destination port 5000 source host 220.181.28.42 source port 80 5. packet sent to the client destination host 192.168.0.5 destination port 1025 source host 220.181.28.42 source port 80