CIDR to IP range conversion using PowerShell

cidrToIpRange.ps1

# calculate IP address range from CIDR notation
# https://en.wikipedia.org/wiki/Classless_Inter-Domain_Routing

function cidrToIpRange {
    param (
        [string] $cidrNotation
    )

    $addr, $maskLength = $cidrNotation -split '/'
    [int]$maskLen = 0
    if (-not [int32]::TryParse($maskLength, [ref] $maskLen)) {
        throw "Cannot parse CIDR mask length string: '$maskLen'"
    }
    if (0 -gt $maskLen -or $maskLen -gt 32) {
        throw "CIDR mask length must be between 0 and 32"
    }
    $ipAddr = [Net.IPAddress]::Parse($addr)
    if ($ipAddr -eq $null) {
        throw "Cannot parse IP address: $addr"
    }
    if ($ipAddr.AddressFamily -ne [Net.Sockets.AddressFamily]::InterNetwork) {
        throw "Can only process CIDR for IPv4"
    }

    $shiftCnt = 32 - $maskLen
    $mask = -bnot ((1 -shl $shiftCnt) - 1)
    $ipNum = [Net.IPAddress]::NetworkToHostOrder([BitConverter]::ToInt32($ipAddr.GetAddressBytes(), 0))
    $ipStart = ($ipNum -band $mask) + 1
    $ipEnd = ($ipNum -bor (-bnot $mask)) - 1

    # return as tuple of strings:
    ([BitConverter]::GetBytes([Net.IPAddress]::HostToNetworkOrder($ipStart)) | ForEach-Object { $_ } ) -join '.'
    ([BitConverter]::GetBytes([Net.IPAddress]::HostToNetworkOrder($ipEnd)) | ForEach-Object { $_ } ) -join '.'
}

$start, $end = cidrToIpRange "192.168.100.14/24"
Write-Host "Start: $start, end: $end"

$start, $end = cidrToIpRange "10.77.1.1/18"
Write-Host "Start: $start, end: $end"

great script. I'm using powershell 7 so I change the return to a custom object with named parameters:

return [PSCustomObject]@{
    Start = ([BitConverter]::GetBytes([Net.IPAddress]::HostToNetworkOrder($ipStart)) | ForEach-Object { $_ } ) -join '.'
    End = ([BitConverter]::GetBytes([Net.IPAddress]::HostToNetworkOrder($ipEnd)) | ForEach-Object { $_ } ) -join '.'
}

Is the script supposed to support /32?
I apologize if I am missing something!

When I tried it returned for 13.95.147.65/32 the start IP of 13.95.147.66 and end IP of 13.95.147.64
I "hacked" it by replacing lines 28 and 29 with

    if ($maskLen -eq 32) {
         $ipStart =$ipNum
         $ipEnd=$ipNum
    }
   else 
        {
           $ipStart = ($ipNum -band $mask) + 1
           $ipEnd = ($ipNum -bor (-bnot $mask)) - 1
   }

I think the +1/-1 should be removed altogether. That's what I did in my fork after verifying.

Thanks, Just what I needed ;-)

The script is really good but does not work well when the mask is 31 or 32.
For an input 13.105.220.108/31 it will produce a result like:

Start Host: 13.105.220.109
End Host: 13.105.220.108

To fix that just replace lines 28 and 29
$ipStart = ($ipNum -band $mask) + 1 $ipEnd = ($ipNum -bor (-bnot $mask)) - 1

By this
` $ipStart = $ipNum -band $mask
$ipEnd = $ipNum -bor (-bnot $mask)

    if ($maskLength -lt 31) {
        $ipStart += 1
        $ipEnd -= 1
    }`

I've tested this with more than 4000 cidr