Checking TCP Port Response Using PowerShell

From time to time, any administrator has to check service availability on a remote server  by testing remote TCP port response. Meanwhile, everybody got used to doing it quickly using telnet command. For example, to make sure the SMTP service is response on a mail server (by default, it responds at TCP Port 25) it is enough to run telnet ny-msg01.woshub.com 25 command. But starting from Windows 7, the telnet client has become a feature to be installed separately. Let’s see how to check for open TCP port using PowerShell.

A ready-to-use cmdlet to check network connection — Test-NetConnection – has appeared in PowerShell 4.0 (Windows 2012 R2, Windows 8.1or higher). It is a part of NetTCPIP module.

Let’s check if TCP Port 25 (SMTP protocol) is available on the mail server using Test-NetConnection:

Test-NetConnection -ComputerName ny-msg01 -Port 25

The shortened version of the same command looks like this:
TNC ny-msg01 -Port 25

Let’s consider the result of the command:

ComputerName           : ny-msg01
RemoteAddress          : 10.20.1.7
RemotePort             : 25
InterfaceAlias         : CORP
SourceAddress          : 10.20.1.79
PingSucceeded          : True
PingReplyDetails (RTT) : 0 ms
TcpTestSucceeded       : True

As we can see, the specified server responds via ICMP (PingSucceeded = True) and TCP Port 25 also responds (RemotePort=25, TcpTestSucceeded= True)

If you only need to see if the port is available, it can be checked in a shorter way:

TNC ny-msg1 -Port 25 -InformationLevel Quiet

The following command allows to check the availability of a specific port on a number of servers, the list of which is stored in a plain text file list_servers.txt. We need the servers without the response from the specific service:

Get-Content c:\PS\list_servers.txt |  where { -NOT (Test-Netconnection $_ -Port 25  -InformationLevel Quiet)}| Format-Table -AutoSize