What is a network port

         As an operation and Maintenance Engineer , Even if it's not specialized in the Internet , I should have heard the concept of port , Then ask you a few small questions , See if you can answer ？？？

• What is a network port ？
• What is the port number ？
• Port number classification
• The role of the port number ？
• How to view the local port number

        Windows

        Linux

• IT The port number that personnel must know

         In view of these problems mentioned above , Do a science popularization for friends who need to know . Everyone has Internet ports on their computers （ Mostly replaced by wireless modules ）、USB Interface , These are actually ports , It is used for external connection , It is called hardware port here ; On the contrary, the network interface we usually mention is naturally the software port , Why software port ？ Because it is originally used for “ Logical connection ”, Simply put, it is a port dedicated to the communication between programs , The communication links between programs are not visible to the naked eye , So it's logical connection . A port is the endpoint of a logical link , Therefore, a program will use the port when sending information . Ports are mainly used in the transport layer , to TCP 、UDP Agreement to use .

        Port number Is a number assigned to the port , Range is from 0 To 65535. Always distinguish between them , It's like whether people have names .

        port It can be divided into three categories , System ports 、 Register port and private port . System port (Well Known Ports): from 0 To 1023, They are tightly bound to some services . Usually, the communication of these ports clearly indicates a certain service The agreement of service . for example :80 Ports are actually always HTTP Communications ,443 Ports, etc . Registered port (Registered Ports): from 1024 To 49151. They are loosely bound to some services . That is to say, there are many services bound to these ports , These ports are also used for many other purposes . for example : Many systems handle dynamic ports from 1024 Start around , for example mysql Of 3306 port . Dynamic and / Or private port (Dynamic and/or Private Ports): from 49152 To 65535. Theoretically , These ports should not be assigned to services . actually , Machines usually come from 1024 Start allocating dynamic ports . But there are exceptions :SUN Of RPC Port from 32768 Start

         The role of the port number It is used for communication between programs , The service functions of each network are different , Therefore, it is necessary to send different packets to different services for processing , When your host is turned on at the same time FTP And WWW The service , Data packets sent by others , According to TCP above port Give me the number FTP This service or WWW This service deals with . A simple example , Tom's house has 5 A door , Entering from different doors can have different results , For instance from 1 Enter through the door , You can sleep in the master bedroom , from 2 Enter through the door , You can enter the kitchen to cook , from 3 You can go to the bathroom when you enter through the door …… The door here can be understood as a port , Entering from different doors and doing different things is similar to what we call programs or services with different functions . As for this house, it is equivalent to IP Address , Therefore, we can also see a IP An address can have multiple port numbers . Like your computer IP The address is 192.168.1.3, But the various services on your computer have many port numbers .

        View port number have access to netstat command , The following figure shows that windows and linux How to view the port number .

windows

LINUX

 

Common port number

20： File transfer protocol (FTP) The data transfer

21： File transfer protocol (FTP) Command control

22：SSH

23：Telnet

25：SMTP, Simple mail transfer protocol

53：DNS

80：HTTP

123：NTP, Network time protocol

161：SNMP, Simple network management protocol

443：HTTPS