Introduction to NAT principles, NAT principles and rules

1. The basic principle of NAT is to use a machine as the gateway router of the virtual network, and build such a network segment for internal network communication with the external network. Traffic can only go in and out of the host that acts as a gateway. NAT routers have at least one global IP

2. NAT is used for:In the scenario where the internal local IP address wants to communicate with the Internet

3. Working mode of NAT: When communicating between the intranet IP and the extranet, the IP address is converted by the rules of the conversion table to access the global network. The destination host receives the packet and thinks it is sent by NAT, and returns it to NAT after processing, and NAT converts the IP again and replies to the source host.

4. A total of 3 columns:

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

Full Cone NAT: All requests from the same internal Tuple X are translated by NAT to the same external Tuple Y, regardless of whether they belong to the same application or multiple applications.

In addition, when the X-Y translation relationship is established, any external host can send UDP packets to the internal host at any time with the address and port in Y as the destination address and destination port.

The NAT method can be used when some hosts in a private network have been assigned a local IP address, but now want to communicate with hosts on the Internet. This method requires the installation of NAT software on a router connected to the Internet on the dedicated network for raiding and destroying. A router with NAT software is called a NAT router, and it has at least one valid external global IP address.

In this way, all hosts that use a local address will have to translate their local address into a global IP address on the NAT router to connect to the Internet when communicating with the outside world.

NAT operation process: 1. Accept data 2. Convert IP according to the conversion relationship table, and save the conversion relationship to memory 3, ** data 4, and return data.

NAT Basic TermsInternal Local Address: The internal address that is translated (usually the private IP address within the enterprise) The internal global address: The external address that is translated (usually the public IP address owned by the enterprise) The external local address:

It is usually used in enterprises that need to provide services outward, such as web server and FTP server outward conversion. 2. The mapping of network segments to network segments, that is, one network segment as a whole is alluded to another network segment. Heng Zheng Mo is usually used in situations where there is a conflict between the addresses of the two parties to the communication, or when the real address needs to be hidden.

3. Dynamic port mapping (PAT), a dynamic mapping of multiple addresses corresponding to one address. The most common situation is when an enterprise accesses the Internet, and the entire company shares the same public IP address. 4. Static port mapping (PAR), multiple addresses are statically mapped to the same address, and the port is fixed.

The most common is that the same public IP address can be used for different ports to provide different services, corresponding to different servers within the enterprise, such as web, mail, ftp, etc., 80 for web, 8000 (for example) mail for ftp.