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Port number

Protocol port number:

The full name of the port number is the protocol port number, which is used for the interaction between the application layer and the transport. When creating a socket, you need to know the ip address and port number. The port number here is virtual. In the transport layer protocol, we know that the port number is a 16-bit integer, so it represents as many port numbers as 0 to 65535. What is the use of it?

If ip is the only host in the network, then ip plus port number is the only process in determining the only host in the network. Note that the port number refers to the local meaning, only in order to mark the interlayer interface when each process in the application layer of the computer interacts with the transport layer, the port numbers of different computers in the Internet are not associated.

Most of the well-known port numbers are retained in the etc/services file.

Classification of protocol port numbers:

1 >. The port number used on the server side: this is divided into two categories, the most important one is known port number or system port number, the value is 0: 1023, these values can be found in the URL www.iana.org. IANA assigns these port numbers to some of the most important applications in TCP/IP and makes them known to all users. When a new application appears, IANA must assign him a familiar port, otherwise other application processes on the Internet will not be able to communicate with him. The other category is the registered port number, which is used by applications that are not familiar with the port number, and the use of this kind of port number must be at the required procedure level in IANA to prevent duplication.

2 >. The port number used by the client: the value is 49152 / 65535. Because this kind of port number is only dynamically selected when the client process is running, it is also called a short port number which is left to the client process to choose to use temporarily. When the server process receives the message from the client process, it knows the port number used by the client process, so it can send the data, and the port number used at the end of the communication no longer exists.

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