Check for open ports: how to do this?

How can I check for open ports?

In this post we are going to explain to you, how can you check for open ports.

What does it mean “check for open ports”? It simply means that a TCP or UDP port is configured to receive data packages. The opposite – when a port declines data packages, it means that this port is closed.

You can check for open ports either on your own computer or on remote one. The main reason to check for open ports is when you are not able to connect to a particular server with particular service.

For example: you are not able to connect to your mail server, so you can’t send mails.

There are a lot of programs, which could check for open ports. There are even online ones. All you need to do, is to write in Google “check for open ports” or “port scanner”.

But here in this post we are going to explain how you could check for open ports by yourself, without any additional software. This could be done using telnet client which is already installed on your Windows.

How to check for open ports in Windows?

 

Important: If you are using Windows XP your telnet is already installed, but if you are using Windows Vista, 7, 8 or 10 you should start it manually, using the following steps:

go to Start menu -> Control Panel -> Programs and Features -> Turn Windows features on or off -> Mark Telnet Client -> press OK.

In order to start telnet, press Windows button + R and then write down cmd. This command will open your Command Prompt (a black window). Now, if you want to check for open ports like port 25 for example, write down the following command:

telnet <your IP> <port number>
Example: telnet 77.70.55.121 25

 

 

Now, after you’ve wrote down the command, press Enter. The telnet client has two types of respond:

1. Connecting To77.70.55.121…Could not open connection to the host, on port 25:Connect failed
This means that port 25 on address77.70.55.121 is closed.

Check for open ports: closed port

Check for open ports: closed port

If the port of the IP address is open, there should be an instant connection.
If the port of the IP address e configured not to respond when someone tries to connects through it, there will be a pitch black screen (Command Prompt) or, if configured with a message, there will be a message like this:

Check for open ports: not responding port

Check for open ports: not responding port

Important: some ports might be closed by your Antivirus software, Firewall or Router.

Now you know how to check for an open port. Simple, isn’t it?

For other useful posts, please visit our Library.

 

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