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)) {
        write-warning "No mask, setting to /32"
        $masklen = 32
    }
    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)
    $ipEnd = ($ipNum -bor (-bnot $mask))

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

# Test
$ips = @('1.2.3.4/24', '9.8.7.6')
$ips | % { cidrToIpRange $_ } | sort-object start

Yup, you're right. Updated.

Thanks for this. I've taken a copy of this function to use in a PS module I'm working on at work for managing Exchange server Receive Connectors' RemoteIPRanges. Only change I made was a "#Credits: " line at the top. Thanks very much and nicely done.