Virtual Geek

This article dives into the Test-TcpPort function, a compact script that resolves hostnames to IPs, pings for basic reachability, and tests port connectivity with a timeout. I will break down its mechanics in short. At its core, Test-TcpPort leverages .NET's System.Net and System.Net.Sockets namespaces for low-level networking checks, wrapped in PowerShell's object-oriented paradigm. Here's the full code for reference:

 function Test-TcpPort {
    param (
        [parameter(Mandatory)][String]$ComputerName,
        [parameter(Mandatory)][Int]$Port,
        [parameter(Mandatory=$false)][Int]$ConnectionTimeout = 500 # Timeout in milliseconds
    )
    try
    {
        $hostEntry = [System.Net.Dns]::GetHostAddresses($ComputerName)
        $ip = ($hostEntry | Where-Object AddressFamily -eq 'InterNetwork').IPAddressToString
    }
    catch
    {
        $ip = $ComputerName
    }
    try
    {
        $ping = New-Object System.Net.NetworkInformation.Ping
        $pingReply = $ping.Send($ip)
        if ($pingReply.Status -eq 'Success')
        {
            $pingStatus = $true
        }
        else {
            $pingStatus = $false
        }
    }
    catch
    {
        $pingStatus = $false
    }
    $tcpClient = New-Object System.Net.Sockets.TcpClient
    $portConnectionStatus = $false
    try {
        $connectAsync = $tcpClient.BeginConnect($ip, $Port, $null, $null)
        $waitHandle = $connectAsync.AsyncWaitHandle
        if ($waitHandle.WaitOne($ConnectionTimeout, $false)) {
            $tcpClient.EndConnect($connectAsync)
            $portConnectionStatus = $true
        }
    }
    finally {
        $tcpClient.Close()
        $waitHandle.Dispose()
    }
    $result = [pscustomobject]@{
       ComputerName = $ComputerName
       IP = $ip
       PingStatus = $pingStatus
       PortConnectionStatus = $portConnectionStatus
    }
    return $result
}

$computers = "ad001", "server1", "psdomain02", "192.168.34.39"
$computers | ForEach-Object {Test-TcpPort -ComputerName $_ -Port 445}

This script is way faster than the earlier written article Building a Unified Ping and Port Connectivity Report with PowerShell and Parallel Ping and Port Testing in PowerShell Using Runspaces

In the script:

Step 1: DNS resolution uses [System.Net.Dns]::GetHostAddresses(), filtering for IPv4 (InterNetwork) to grab the first available IP. 
Step 2: Next, it instantiates a Ping object from System.Net.NetworkInformation and sends a single ICMP echo to the resolved IP. Success sets $pingStatus to $true; failures (timeouts, blocks) default to $false.
Step 3: Asynchronous TCP Connection Test - A TcpClient attempts a non-blocking connect via BeginConnect(), paired with an AsyncWaitHandle for timeout enforcement.

Below are the different way you can use and execute function Test-TcpPort.

$computers = "ad001", "server1", "psdomain02", "192.168.34.39"
$computers | ForEach-Object {Test-TcpPort -ComputerName $_ -Port 445}

Get-Content servers.txt | ForEach-Object { Test-TcpPort -ComputerName $_ -Port 443 } | Export-Csv -Path portscan.csv
1..3 | ForEach-Object { Test-TcpPort -ComputerName "target" -Port (22 + $_) } #for sequential ports.

Download this script ping_port_scanner_powershell.ps1 or it is also available on github.com.

It reduces Overhead: Avoids the heavier cmdlets like Test-Connection and Test-NetConnection when you only need basic port checks.

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