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In network technology, ports generally have two meanings: one is the port in the physical sense, and the other is the port in the logical sense, which generally refers to the port in the TCP/IP protocol, and the port number ranges from 0 to 65536, such as port 80 for browsing web services, port 21 for FTP services, and so on.

Port classification

According to the nature of the port, it can be divided into the following three categories:

(1) well-known port (Well Known Ports): this type of port is also called "common port" and is numbered from 0 to 1024. They are tightly tied to specific services. Usually the communication of these ports clearly indicates the protocol of a service, and these ports can no longer redefine its object. For example, port 80 is actually always used for HTTP (Hypertext transfer Protocol) communications, while port 23 is dedicated to Telnet services.

(2) Registration port (Registered Ports): the port number is from 1025 to 49151. They are loosely tied to some services. That is, there are many services tied to these ports, which are also used for many other purposes. Most of these ports do not clearly define service objects, and different programs can define them according to their actual needs. For example, these ports are defined in remote control software and * * programs (keep in mind that these common program ports are very necessary in the protection and killing of * programs).

(3) dynamic and / or private port (Dynamic and/or Private Ports): the port number is from 49152 to 65535. In theory, these ports should not be assigned to services. In fact, some special programs, especially some programs, like to use these ports, because these ports are often unnoticed and easy to hide.

In the more than 60, 000 ports of the computer, those with port numbers less than 1024 are usually called common ports, and the services corresponding to these common ports are usually fixed. Table 1 lists the default ports of the server, which are not allowed to change. These ports are mainly used in the general communication process.

The commonly used reserved TCP port numbers are:

HTTP 80, FTP 20, etc. 21, Telnet, 23, SMTP, 25, DNS 53, etc.

The commonly used reserved UDP port numbers are:

DNS 53 Magi BootP 67 (server) / 68 (client), TFTP 69 Magi SNMP 161, etc.

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