Port concept

In network technology, ports have two meanings: one is physical ports, such as interfaces used by ADSL modems, hubs, switches and routers to connect other network devices, such as RJ-45 ports and SC ports. The second is logical port, which generally refers to the port in TCP/IP protocol. Port numbers range from 0 to 65535, such as port 80 for browsing web services, port 2 1 for FTP services and so on. What I want to introduce here is the logical port.

(1) well-known ports

Well-known ports are well-known port numbers from 0 to 1023, which are generally assigned to some services. For example, port 2 1 is assigned to FTP service, port 25 is assigned to SMTP (Simple Mail Transfer Protocol) service, port 80 is assigned to HTTP service, port 135 is assigned to RPC (Remote Procedure Call) service and so on.

(2) Dynamic port.

Dynamic ports range from 1024 to 65535, and these port numbers are generally not fixed to a service, which means that many services can use these ports. As long as a running program requests the system to access the network, the system can assign one of these port numbers to the program. For example, port 1024 is assigned to the first program that sends an application to the system. After closing the program process, the occupied port number will be released.