1, the basic principle of NAT is to use a machine as the gateway router of the virtual network and build a network segment similar to 192. 168 ... xxx.xxx for communication between the internal network and the external network. Traffic can only enter and exit through the host as a gateway. A NAT router has at least one global ip.

2.NAT is used in the scenario where the internal local ip wants to communicate with the external network.

3. The working mode of NAT: When the internal network ip communicates with the external network, it goes through NAT first, and the ip address is converted by the rules of the conversion table before accessing the global network. The destination host receives the packet and thinks it was sent by NAT. After processing, it returns to NAT, which performs ip conversion again and returns to the source host.

4, a total of ***3 columns:

Direction (in/out), old ip and port number, new ip and port number.