User interface to telnet protocol


When it comes khổng lồ checking if a network port is opened or closed on a remote computer, there’s no easier way than to lớn use Telnet. Ports that are left xuất hiện for no reason are a security risk that can be exploited by malicious programs và viruses. At the same time, if a legitimate software communicates through a certain port, having that port closed will make the program throw errors & malfunction.

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Many people find the challenge of checking if a port is opened khổng lồ be too complex. However, one of the most efficient ways is to use the network protocol Telnet. Telnet allows the user to chạy thử individual ports and see whether they are open or not. In this article we’ll break down how Telnet can be used to check ports on Windows 10, Windows server 2016, 2012 và 2008.

What is Telnet?

In a nutshell, Telnet is a computer protocol that was built for interacting with remote computers.

The word “Telnet” also refers lớn the command-line utility “telnet”, available under Windows OS & Unix-like systems, including Mac, Linux, & others. We will use the term “Telnet” mostly in the context of the telnet client software.

Telnet utility allows users to test connectivity to lớn remote machines và issue commands through the use of a keyboard. Though most users opt khổng lồ work with graphical interfaces, Telnet is one of the simplest ways to kiểm tra connectivity on certain ports.

Enabling telnet client in Microsoft Windows operating systems

One of the most important things to lớn remember is that Telnet is disabled by default in Window’s settings, so you need lớn turn it on before you can bởi vì anything. Turning it on will help you to run the required diagnostics and kiểm tra if a port is open. If you try to use telnet without turning it on first, you’ll receive a message like: 

 ‘telnet’ is not recognized as an internal or external command, operable program or C:>

In order khổng lồ turn Telnet on, you need khổng lồ use the command line or the graphical interface of your computer.

Enabling telnet client through Command Prompt:

If you want to enable Telnet via the command line, xuất hiện the Command Prompt with elevated privileges (“as Administrator”) and run the following command:

Dism /Online /Enable-feature /FeatureName:TelnetClient

After you’ve put this in, Telnet will be ready to use to check your ports. 

Alternatively to Command Prompt, you can use the following PowerShell command to lớn achieve the same result:

Install-WindowsFeature -name Telnet-Client

If you want to use the graphical user interface you need to: 

Windows 7, 8. 10:

Open Windows Start menu > Type "Control Panel" > Press Enter > “Programs” > "Programs và Features" > Turn Windows features on or off > Select "Telnet Client" > Press “OK"

Windows server 2008:

Open “Server Manager” > Features > click “Add Features” > enable “Telnet Client” checkbox > click “Next” > click “Install” > when the feature installation finishes, click “Close”

Windows server 2012, 2016:

Open “Server Manager” > “Add roles & features” > click “Next” until reaching the “Features” step > tick “Telnet Client” > click “Install” > when the feature installation finishes, click “Close”.

Using Telnet to Test xuất hiện Ports

One of the biggest perks of Telnet is with a simple command you can kiểm tra whether a port is open. Issuing the Telnet command telnet will allow you to chạy thử connectivity lớn a remote host on the given port. 

Issue the following command in the Command Prompt:


Put the IP address or domain name of the server you’re trying khổng lồ connect to in place of , và replace the second brackets with the port number on the remote machine, connection to lớn which you want to test.

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For example, khổng lồ verify connection to lớn on port 25, issue the command:

telnet 25

If the connection succeeds, a blank screen will show up, meaning that the computer port is open.

A failed connection will be accompanied by an error message. It can indicate either a closed port or the fact that the indicated remote server is not listening on the provided port.


telnet 443


How to check if a Port is mở cửa on Mac

High Sierra users: táo khuyết removed telnet client from macOS 10.13 High Sierra. There is no official way to return it, but you can still copy it from an older OS or compile from sources và use on High Sierra. See more details here & here.

Just lượt thích on Windows, telnet can be accessed through Terminal, the command prompt on macOS. To mở cửa telnet, click “Go” > “Utilities” > "Terminal", then run the following command (the numbers are example IP address & port): telnet , e.g.>telnet 443

When a computer port is open a blank screen will show up, meaning that the connection has been successful. An unsuccessful connection will be accompanied by an error message. 

An alternative khổng lồ telnet in checking ports is Network Utility. In order to kiểm tra ports on a Mac, follow the plan below:

Open "Network Utility" > Click "Port Scan" > Indicate the hostname and ports khổng lồ scan the remote host e.g. from 995 to lớn 995 > check the output 

Acting on the results obtained from the Telnet test

Many times when you try to use Telnet, you may find that your own network is blocking your connection. It’s quite common for users to lớn be running a firewall, which blocks connection, outbound ports. A basic way to demo whether your firewall is interrupting your Telnet is lớn disable your firewall & run a Telnet test. 

If you want to kiểm tra for closed ports on your router, enter your router management console. Open a web browser and enter the IP address or name of the router, for example “”. If the page does not open, try replacing “http” with “https” at the beginning of the address.

Next, enter your username và password, và click “Enter” or “Log in”. Head lớn the Security section to mở cửa or close ports & access other firewall settings of the router.

If you need khổng lồ make resources in the internal network accessible from the outside, enter “External access”/”Port forwarding” section. Consult the router manufacturer’s documentation for the detailed instructions.

Related resources

Read further on what ports are used in software and how to mở cửa them:




A summary page about the network ports used in software

Instructions for using software with Microsoft Azure (the required ports part).

Troubleshooting instructions: what you need to vì to proper configure the network environment và in which order

List of ports used in Cyber Backup Cloud, Backup Service, Backup 12, Backup 12.5

List of ports used in Backup 11.7 và earlier versions, and True Image

Alternative to lớn Telnet, a specialized tool for testing ports for Cyber Backup Cloud, Backup 12 и Backup 12.5

Alternative to lớn Telnet, a specialized tool for testing ports for Backup 11.7 và earlier versions, and True Image