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Network ports - what they are

There are two types of ports in computers: physical ports and software ports, also called network ports. A physical port is a connector that allows you to connect various devices such as thumb drives, network cables, printers, headphones, and more.
Today, almost all the programs we use on our computers work through a network protocol. Many people know about the existence of network ports, but not everyone understands what exactly they mean and how they work.

What is a port on a network

A network port is like a magic door that is added to an IP address to make it possible to transmit data. You need to configure it - assign a number from 0 to 65535. It is recorded in certain parts of the message and helps you find the right application to process the information.
The main purpose of ports is to exchange data of a certain type, and to eliminate the ambiguity that arises when trying to communicate with a host by its IP address. To transfer data from a web server, you must specify the host IP address and port number.
Imagine an apartment building where each apartment is a unique destination for the letter carrier. The address of the building is the IP address. When the letter carrier approaches the house (IP address), he doesn't know which apartment to go to until he reads the apartment number (port) on the envelope. And there may only be 65,535 apartments in that house.

What network ports are for

  • The operating system requests security updates through a specific port on the server.
  • The browser loads pages.
  • Various messengers send and receive messages through their ports.
  • A background program may use a port for video calling and video data transfer.
  • Cloud services use ports to synchronize data.

How a computer's network ports work

A port is a number in the range of 1 to 65535 that is used by applications to communicate on a network.
There are several transport protocols, of which the most common are TCP/IP (Transmission Control Protocol/Internet Protocol) and UDP (User Datagram Protocol). These protocols enable the transfer of information between different applications and devices.
When an application communicates, it can wait for incoming data or a connection request, or it can send data or a connection request to a known port that is opened by the server application (in the client role).
By default, an application is assigned a port with an arbitrary number, such as the next available port after 1234. However, an application can request a specific (predefined) port. For example, web servers typically use the predefined TCP port 80 to wait for connections.
TCP and UDP ports do not overlap. This means that TCP port 1234 will not interfere with UDP communication over UDP port 1234. This separation allows devices to communicate efficiently, avoiding conflicts and ensuring proper routing.

Examples of use

When a user opens a browser window and enters a query, the web server automatically sends data on port 80 using TCP/IP.
If you are using the Outlook Express email client, port 110 is used to receive emails and port 25 is used to send emails.

Actions with ports - opening, closing, forwarding and others

You can perform various actions with the ports:
  • Open port - allows the system to know where to send data.
  • Close - stops transmitting data on this port. In this case, the data will be ignored.
  • Forward Port - allows you to configure the system so that requests received on a particular port are sent to another port. This is often used in network routers and by Internet providers.
  • Scan ports - go through all possible numbers (from 0 to 65535) to see if there is a response from a program on one of them.
  • Block - configuring your router so that all requests to a particular port are dropped or forwarded.
  • Assign - If you know that a certain port is blocked, you can assign another port to that program and send data through it.
It is important to note that ports can also be opened by malicious programs without the user's knowledge. This allows them to obtain information from the computer. Therefore, it is important to know how to open and close ports to protect your system.

Server security and ports

Every open port is a potential target for malware. Therefore, regular scanning is necessary to detect all open ports that should not be in this status. The process helps to identify security vulnerabilities and prevent unauthorized access to the network.

The best known network ports:

  • FTP (File Transfer Protocol) - 20 and 21.
  • SSH (Secure Shell) - 22.
  • Telnet - 23.
  • SMTP (Simple Mail Transfer Protocol) - 25.
  • DNS (Domain Name System) - 53.
  • DHCP (Dynamic Host Configuration Protocol) - 67 and 68.
  • HTTP (hypertext transfer protocol) - 80 and 443.
  • POP3 (Post Office Protocol version 3) - 110.
  • IMAP (Internet Message Access Protocol) - 143.
  • RDP (Remote Desktop Protocol) - 3389.

Network port ranges, numbers and list

Port numbers in network communication are divided into three main ranges: standard, registered, and dynamic (private).
Standard ports represent a range of values from 0 to 1023 for the widely used HTTP (80), FTP (21) and SSH (22) protocols. They play an important role in providing basic network communication functions.
Registered ports are from 1024 to 49151. These are intended for protocols and services that are not standard but require registration in the Internet registry. This avoids conflicts between different applications and services.
Dynamic or private ports are from 49152 to 65535. Used by the operating system to temporarily assign ports when establishing connections between two devices. They do not require registration and can be used for temporary communication.
So memorizing which port is used to identify each service is a futile exercise.

The most important network ports and their purpose

A thorough understanding of ports and protocols is an essential requirement in networking. Ports act as endpoints for connections, and protocols define a set of rules that govern the transfer of information.
An important example is HTTP (port 80), which is used to transfer data using the HTTP protocol. It is the basic element of working with web servers, provides the ability to browse web pages, download files and send data to the server.
Another significant port is FTP (port 21), which is used to transfer files between a computer and a server. It provides a reliable connection and allows users to upload and download files, as well as modify and manage server content.
SMTP (port 25) is the third port that deserves attention. It is used to send and receive emails, providing security and spam protection.
Finally, it is important to mention SSH (port 22), which is responsible for secure remote access. It is used for data encryption and user authentication. SSH also provides administrators with the ability to manage the server remotely from anywhere in the world.

Network port table - what is it?

The Network Ports List is an essential tool for professionals working in Information Technology Services. The table provides comprehensive information about ports and their assignments. It is critical for troubleshooting possible network problems and maintaining proper device configuration.
The lack of a table can make it difficult to identify open and closed ports, leading to security breaches and performance issues

Basic things to know about network ports

When a packet is sent to your computer's IP address, the question becomes what to do with it and to whom it is addressed. Depending on the destination, the packet could be anything: part of a video, a messenger message, or an update for the Windows operating system. When the packet arrives at the computer, it is transmitted by port number to the appropriate program that is pre-registered to handle such data.
Thus, ports play an important role in determining the target application or program that will process the data, which enables efficient transfer of information on the network.
28 Apr 2024, 16:12:04