SOSysAdmin - How to test if a port is open on a remote machine

How to test if a port is open on a remote machine

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Verifying if a port is open on a remote machine.

construction How-to
There are 2 quick ways to check if a port is open on a remote host:

Using Telnet (the old-fashioned way)
Using PowerShell

Option 1 – Using Telnet

Assuming Telnet is installed on your Windows machine:

Open a command prompt or a PowerShell
Execute the following command:

telnet "remote host" "port"

remote host: : the IP or DNS name of the remote machine (Note: you can't specify a protocol, so google.com will work, while https://google.com won't)
port: the port number

So, if you want to test the connection to port 443 (HTTPS) on google.com simply run:

telnet google.com 443

There are two possible outcomes:

The port is open and you will get an empty prompt awaiting for your input (depending on the service running behind that port)
The port is closed/not listening. This will be noticeable by an error message like this:

Could not open connection to the host, on port 443: Connection failed

Option 2 – Using Telnet

The modern way to test a connection using the Test-NetConnection cmdlet:

Open a PowerShell
Execute the following command:

Test-NetConnection -ComputerName "remote host" -Port "port number"

remote host: : the IP or DNS name of the remote machine (Note: you can't specify a protocol, so google.com will work, while https://google.com won't)
port: the port number

So, if you want to test the connection to port 443 (HTTPS) on google.com run:

Test-NetConnection -ComputerName google.com -Port 443

The output will be similar to this:


    ComputerName      : google.com
    RemoteAddress     : 142.250.184.110
    RemotePort        : 443
    InterfaceAlias    : Ethernet
    SourceAddress     : 192.168.0.1
    TcpTestSucceeded  : True

You can check the outcome by looking at the last line, TcpTestSucceeded, which can be either true or false.
While it's not the quickest way to test a single port, the Test-NetConnection cmdlet has a lot of other useful options and use cases.
You can find the link to the documentation at the end of this page.

school Further considerations

Remember that if you "opened" a port but there isn't a running service listening on that port (example: you allowed incoming packets on port 80 but your NGINX server is not running) it will be reported as closed
You can read more about the Test-NetConnection cmdlet on the official Microsoft documentation

Article ID: SYS-WIN-0009