1、 Definition of port
The port number identifies the only process in the host, and the IP + port number identifies the only process in the network. In the socket programming we usually use, the IP + port number is the socket
The port number is a 16 bit process number, ranging from 0 to 65535. In principle, you can use these ports freely. But you are not a VIP user, so some ports are occupied by VIP users. For example, FTP 21, SSH 22, etc., so ports are classified to specify the range of ports you can use.
2、 Port classification
1. Hardware port
The CPU transmits data with peripherals through interface registers or specific circuits, which are called ports.
The ports in the hardware field are also called interfaces, such as parallel ports, serial ports, etc.
2. Network port
In network technology, port has several meanings. The port of hub, switch and router refers to the interface connecting other network devices, such as RJ-45 port, serial port, etc. the port we refer to here does not refer to the physical port, but specifically refers to the port in TCP / IP protocol, which is a logical port.
3. Software port
3、 Function of port
Someone once compared a server to a house, Comparing ports to doors leading to different rooms (services) is a good metaphor if details are not considered. If an intruder wants to occupy the house, he is bound to break through the door (physical invasion is another word). Therefore, it is very important for an intruder to understand how many doors the house opens, what kind of doors they are, and what is behind the door.
Intruders usually scan the ports of the target host with a scanner to determine which ports are open. From the open ports, intruders can know what services the target host provides, and then guess possible vulnerabilities. Therefore, scanning the ports can help us better understand the target host. For administrators, Scanning the open port of this machine is also the first step of security.