PowerShell Subnet Overlap

subnet-overlap.ps1

function ConvertTo-IPv4MaskString {
    [CmdletBinding()]
    param(
        [Parameter(Mandatory = $true)]
        [ValidateRange(0, 32)]
        [int]
        $MaskBits
    )
    $mask = ([System.Math]::Pow(2, $MaskBits) - 1) * [System.Math]::Pow(2, (32 - $MaskBits))
    $bytes = [System.BitConverter]::GetBytes([UInt32] $mask)
    (($bytes.Count - 1)..0 | ForEach-Object { [string] $bytes[$_] }) -join '.'
}

function Test-SubnetOverlap {
    [CmdletBinding()]
    param (
        [Parameter(Mandatory = $true)]
        [string]
        $Subnet1,

        [Parameter(Mandatory = $true)]
        [string]
        $Subnet2
    )

    $subnetParts1 = $Subnet1.Split('/')
    $subnetParts2 = $Subnet2.Split('/')

    $address1 = [System.Net.IPAddress]($subnetParts1[0])
    $address2 = [System.Net.IPAddress]($subnetParts2[0])

    $mask1 = [System.Net.IPAddress]::Parse((ConvertTo-IPv4MaskString -MaskBits ([int]($subnetParts1[1]))))
    $mask2 = [System.Net.IPAddress]::Parse((ConvertTo-IPv4MaskString -MaskBits ([int]($subnetParts2[1]))))

    ($address1.Address -band $mask1.Address) -eq ($address2.Address -band $mask2.Address)
}

Tests if two subnets overlap e.g.

C:\> Test-SubnetOverlap -Subnet1 "192.168.1.0/24" -Subnet2 "192.168.1.0/24"
True

C:\> Test-SubnetOverlap -Subnet1 "192.168.1.0/24" -Subnet2 "192.168.2.0/24" 
False