Network programming-port classification research and NETSTAT commands

Port of Transport layer :

1. What is a port? Why do I use a port?

Process creation and revocation are dynamic, the side of the communication can hardly recognize the process on the other machine, we need to use the function provided by the destination host to identify the endpoint.

So in order to solve the above problem, we use the Protocol port number (port) in the transport layer

2. What are the categories of ports?

Software Port: An abstract protocol port between the protocol stack layers

A software port is an address that is used by the various protocol processes in the application layer to interact with the transport entity between layers.

Hardware ports: Routers, interfaces on the switch, etc.

Hardware ports are interfaces that interact with different hardware device processes

3. What is a port number? Why use the port number?

The transport layer of TCP/IP flags a port with a 16-bit port number (port number only has local meaning )

The port number is used to flag the interface between each process and transport layer in the application layer of this computer (in the Internet, different PCs, the same port number is not associated)

4. Transport Layer port number classification?

　　

5. What are the common ports in network services? What is the respective port number?

　

SNMP trap: A type of ingress that arrives at the ingress that enables SNMP-managed devices to proactively notify the SNMP manager instead of waiting for the SNMP manager to poll again

6.netstat command

The netstat command is used to print the status information of network systems in Linux, allowing you to learn about the network conditions of the entire Linux system.

　　

List all TCP ports

List all UDP ports

List all listening Unix ports only

　　

　　

Network programming-port classification research and NETSTAT commands