Get-UsableAddressSpace.ps1

function Get-UsableAddressSpace {
    param (
        [Parameter(Mandatory = $true)]
        [string]$CIDR
    )

    # Function to convert IP address to integer
    function ConvertTo-Int {
        param ($ip)
        $i = 0
        $ip.Split('.') | ForEach-Object { [int]$_ } | ForEach-Object { $_ -shl 8 * (3 - $i++) } | Measure-Object -Sum | Select-Object -ExpandProperty Sum
    }

    # Function to convert integer to IP address
    function ConvertTo-IP {
        param ($int)
        $bytes = 3..0 | ForEach-Object { ($int -shr 8 * $_) -band 255 }
        return ($bytes -join '.')
    }

    # Extract base IP and subnet mask
    $baseIP, $prefix = $CIDR -split '/'
    $prefix = [int]$prefix

    # Convert base IP to integer
    $baseInt = ConvertTo-Int -ip $baseIP

    # Calculate subnet mask and network size
    $subnetMask = ([math]::Pow(2, 32) - [math]::Pow(2, 32 - $prefix))
    $networkSize = [math]::Pow(2, 32 - $prefix)

    # Calculate network and broadcast addresses
    $networkInt = $baseInt -band $subnetMask
    $broadcastInt = $networkInt + $networkSize - 1

    # Calculate first and last usable IP addresses
    $firstUsableInt = $networkInt + 1
    $lastUsableInt = $broadcastInt - 1

    # Convert back to IP addresses
    $firstUsableIP = ConvertTo-IP -int $firstUsableInt
    $lastUsableIP = ConvertTo-IP -int $lastUsableInt

    # Output results
    [PSCustomObject]@{
        CIDR            = $CIDR
        NetworkAddress  = ConvertTo-IP -int $networkInt
        BroadcastAddress = ConvertTo-IP -int $broadcastInt
        FirstUsableIP   = $firstUsableIP
        LastUsableIP    = $lastUsableIP
        UsableHostCount = $lastUsableInt - $firstUsableInt + 1
    }
}

# Example usage
Get-UsableAddressSpace -CIDR "192.168.0.0/21"