PowerShell Subnet Calculator

I’m often faced with situations when I need to scan entire subnets to find devices and either perform an inventory or run a remote PowerShell command on all the devices on a subnet. It’s quite simple to generate the list of IPs for a /24 subnet but is a little trickier for the other subnets, e.g. a /12. Anyways, long story short. Here is a PowerShell function that will output an array of all the IPs on a particular subnet. 

You can run it as below:

Get-IPs
-Subnets “10.0.2.0/24″,”10.0.4.0/24”

For example:

You can then pipe out the IPs so you can run a command on each:

Get-IPs -Subnets “10.0.2.0/24″,”10.0.4.0/24” | % {Do something on $_}

The function is below. Happy scripting.

function Get-IPs {

        Param(

        [Parameter(Mandatory = $true)]

        [array] $Subnets

        )

foreach ($subnet in $subnets)

    {

        

        #Split IP and subnet

        $IP = ($Subnet -split “/”)[0]

        $SubnetBits = ($Subnet -split “/”)[1]

        

        #Convert IP into binary

        #Split IP into different octects and for each one, figure out the binary with leading zeros and add to the total

        $Octets = $IP -split “.”

        $IPInBinary = @()

        foreach($Octet in $Octets)

            {

                #convert to binary

                $OctetInBinary = [convert]::ToString($Octet,2)

                

                #get length of binary string add leading zeros to make octet

                $OctetInBinary = (“0” * (8 – ($OctetInBinary).Length) + $OctetInBinary)

                $IPInBinary = $IPInBinary + $OctetInBinary

            }

        $IPInBinary = $IPInBinary -join “”

        #Get network ID by subtracting subnet mask

        $HostBits = 32-$SubnetBits

        $NetworkIDInBinary = $IPInBinary.Substring(0,$SubnetBits)

        $HostIDInBinary = $IPInBinary.Substring($SubnetBits,$HostBits)

        #Work out all the host IDs in that subnet by cycling through $i from 1 up to max $HostIDInBinary (i.e. 1s stringed up to $HostBits)

        #Work out max $HostIDInBinary

        $imax = [convert]::ToInt32((“1” * $HostBits),2) -1

        $IPs = @()

        #Next ID is first network ID converted to decimal plus $i then converted to binary

        For ($i = 1 ; $i -le $imax ; $i++)

            {

                #Convert to decimal and add $i

                $NextHostIDInDecimal = ([convert]::ToInt32($HostIDInBinary,2) + $i)

                #Convert back to binary

                $NextHostIDInBinary = [convert]::ToString($NextHostIDInDecimal,2)

                #Add leading zeros

                #Number of zeros to add 

                $NoOfZerosToAdd = $HostIDInBinary.Length – $NextHostIDInBinary.Length

                $NextHostIDInBinary = (“0” * $NoOfZerosToAdd) + $NextHostIDInBinary

                #Work out next IP

                #Add networkID to hostID

                $NextIPInBinary = $NetworkIDInBinary + $NextHostIDInBinary

                #Split into octets and separate by . then join

                $IP = @()

                For ($x = 1 ; $x -le 4 ; $x++)

                    {

                        #Work out start character position

                        $StartCharNumber = ($x-1)*8

                        #Get octet in binary

                        $IPOctetInBinary = $NextIPInBinary.Substring($StartCharNumber,8)

                        #Convert octet into decimal

                        $IPOctetInDecimal = [convert]::ToInt32($IPOctetInBinary,2)

                        #Add octet to IP 

                        $IP += $IPOctetInDecimal

                    }

                #Separate by .

                $IP = $IP -join “.”

                $IPs += $IP

                

            }

        $IPs

    }

}