When computers communicate with each other, there are two ways: one is to confirm whether the information has arrived after sending, that is, there is a reply, and TCP protocol is often used. In TCP transmission control protocol, the establishment of end-to-end connection depends on the interaction between IP address and TCP port number.

One is to leave it alone after sending it, and not confirm whether the information has arrived. This method mostly adopts UDP protocol, and UDP also uses port number to connect.

The ports provided by services corresponding to these two protocols are also divided into TCP ports and UDP ports.

When you want to access a network application process (such as a WEB service) on another host, the IP packet you send contains not only the IP address of the other host, but also the port number of your access program.

The so-called port monitor means that after receiving an IP packet, the host network process checks whether its destination port is its own port number, and if so, accepts the packet for processing. The host communicating on the network not only sends data, but also receives data, so it is necessary to open the corresponding port to receive data. A host on a network may start multiple network processes (such as browsing web pages and accessing QQ), that is, listening to multiple ports.

If you want to see the open ports of your computer

You can start/run the input cmd to enter the command prompt.

Then enter netstat -a (with spaces in the middle).

So you can see the TCP/UDP port you are listening to.