Subnet mask functions

Since I have no memory (it’s actually this blog’s main purpose!), here is a summary of the possible subnet masks:

Since I’m lazy, look in this table is too tiring… pfff… i’m exhausted of typing…
Let’s use a function (thanks to Chris Dent) to generate the mask from its length, and vice versa!

• Convert a subnet mask to a mask length

Function ConvertTo-MaskLength { 
  [CmdLetBinding()]
  Param(
    [Parameter(Mandatory=$True, Position=0, ValueFromPipeline=$True)]
    [Net.IPAddress]$SubnetMask
  )
  Process {
    $Bits = "$( $SubnetMask.GetAddressBytes() | ForEach-Object { [Convert]::ToString($_, 2) } )" -Replace '[\s0]'
    Return $Bits.Length
  }
}

• Convert a mask length to a subnet mask

Function ConvertTo-DottedDecimalIP {
[CmdLetBinding()]
  Param(
    [Parameter(Mandatory = $True, Position = 0, ValueFromPipeline = $True)]
    [String]$IPAddress
  )
   
  Process {
    Switch -RegEx ($IPAddress) {
      "([01]{8}\.){3}[01]{8}" {
        Return [String]::Join('.', $( $IPAddress.Split('.') | ForEach-Object { [Convert]::ToUInt32($_, 2) } ))
      }
      "\d" {
        $IPAddress = [UInt32]$IPAddress
        $DottedIP = $( For ($i = 3; $i -gt -1; $i--) {
          $Remainder = $IPAddress % [Math]::Pow(256, $i)
          ($IPAddress - $Remainder) / [Math]::Pow(256, $i)
          $IPAddress = $Remainder
         } )
        
        Return [String]::Join('.', $DottedIP)
      }
      default {
        Write-Error "Cannot convert this format"
      }
    }
  }
}

Function ConvertTo-Mask {
  [CmdLetBinding()]
  Param(
    [Parameter(Mandatory=$True, Position=0, ValueFromPipeline=$True)]
    [ValidateRange(0, 32)]
    $MaskLength
  )
  Process {
    Return ConvertTo-DottedDecimalIP ([Convert]::ToUInt32($(("1" * $MaskLength).PadRight(32, "0")), 2))
  }
}