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More IPv4 subnet maths with PowerShell

Chris — Thu, 13 Oct 2011 11:55:19 +0000

I’ve been extended and upgrading my library of network functions for some time now, I thought I’d post the functions that work directly with my original collection.

These functions are also included in my NetShell module, I need to post an update to that very soon as well.

ConvertTo-HexIP

Sometimes being able to convert to a hexadecimal format is useful, this little function does exactly that. The body is very simple; it uses the built in formatters.

Function ConvertTo-HexIP {
  <#
    .Synopsis
      Converts a dotted decimal IP address into a hexadecimal string.
    .Description
      ConvertTo-HexIP takes a dotted decimal IP and returns a single hexadecimal string value.
    .Parameter IPAddress
      An IP Address to convert.
  #>

  [CmdLetBinding()]
  Param(
    [Parameter(Mandatory = $True, Position = 0, ValueFromPipeline = $True)]
    [Net.IPAddress]$IPAddress
  )

  Process {
    "$($IPAddress.GetAddressBytes() | ForEach-Object { '{0:x2}' -f $_ })" -Replace '\s'
  }
}

ConvertFrom-HexIP

And back again, using System.Convert.ToUInt32 with a base-16 value to get to UInt32, then a call to ConvertTo-DottedDecimalIP (from the original set).

Function ConvertFrom-HexIP {
  <#
    .Synopsis
      Converts a hexadecimal IP address into a dotted decimal string.
    .Description
      ConvertFrom-HexIP takes a hexadecimal string and returns a dotted decimal IP address.
    .Parameter IPAddress
      An IP Address to convert.
  #>

  [CmdLetBinding()]
  Param(
    [Parameter(Mandatory = $True, Position = 0, ValueFromPipeline = $True)]
    [ValidatePattern('^[0-9a-f]{8}$')]
    [String]$IPAddress
  )

  Process {
    ConvertTo-DottedDecimalIP ([Convert]::ToUInt32($IPAddress, 16))
  }
}

Get-NetworkSummary

Get-NetworkSummary gets a bit of an improvement.

Function Get-NetworkSummary {
  <#
    .Synopsis
      Generates a summary of a network range
    .Description
      Get-NetworkSummary uses most of the IP conversion CmdLets to provide a summary of a network
      range from any IP address in the range and a subnet mask.
    .Parameter IPAddress
      Any IP address within the network range.
    .Parameter Network
      A network description in the format 1.2.3.4/24
    .Parameter SubnetMask
      The subnet mask for the network.
  #>

  [CmdLetBinding(DefaultParameterSetName = "IPAndMask")]
  Param(
    [Parameter(Mandatory = $True, Position = 0, ParameterSetName = "IPAndMask", ValueFromPipeline = $True)]
    [Net.IPAddress]$IPAddress,

    [Parameter(Mandatory = $True, Position = 1, ParameterSetName = "IPAndMask")]
    [Alias("Mask")]
    [Net.IPAddress]$SubnetMask,

    [Parameter(Mandatory = $True, ParameterSetName = "CIDRNotation", ValueFromPipeline = $True)]
    [ValidatePattern('^(\d{1,3}\.){3}\d{1,3}[\\/]\d{1,2}$')]
    [String]$Network
  )

  Process {
    If ($PsCmdLet.ParameterSetName -eq 'CIDRNotation') {
      $Temp = $Network.Split("\/")
      $IPAddress = $Temp[0]
      $SubnetMask = ConvertTo-Mask $Temp[1]
    }

    $DecimalIP = ConvertTo-DecimalIP $IPAddress
    $DecimalMask = ConvertTo-DecimalIP $SubnetMask
    $DecimalNetwork =  $DecimalIP -BAnd $DecimalMask
    $DecimalBroadcast = $DecimalIP -BOr ((-BNot $DecimalMask) -BAnd [UInt32]::MaxValue)

    $NetworkSummary = New-Object PSObject -Property @{
      "NetworkAddress"   = (ConvertTo-DottedDecimalIP $DecimalNetwork);
      "NetworkDecimal"   = $DecimalNetwork
      "BroadcastAddress" = (ConvertTo-DottedDecimalIP $DecimalBroadcast);
      "BroadcastDecimal" = $DecimalBroadcast
      "Mask"             = $SubnetMask;
      "MaskLength"       = (ConvertTo-MaskLength $SubnetMask);
      "MaskHexadecimal"  = (ConvertTo-HexIP $SubnetMask);
      "HostRange"        = "";
      "NumberOfHosts"    = ($DecimalBroadcast - $DecimalNetwork - 1);
      "Class"            = "";
      "IsPrivate"        = $False}

    If ($NetworkSummary.MaskLength -lt 31) {
      $NetworkSummary.HostRange = [String]::Format("{0} - {1}",
        (ConvertTo-DottedDecimalIP ($DecimalNetwork + 1)),
        (ConvertTo-DottedDecimalIP ($DecimalBroadcast - 1)))
    }

    Switch -RegEx ($(ConvertTo-BinaryIP $IPAddress)) {
      "^1111"              { $NetworkSummary.Class = "E" }
      "^1110"              { $NetworkSummary.Class = "D" }
      "^11000000.10101000" { $NetworkSummary.Class = "C"; $NetworkSummary.IsPrivate = $True }
      "^110"               { $NetworkSummary.Class = "C" }
      "^10101100.0001"     { $NetworkSummary.Class = "B"; $NetworkSummary.IsPrivate = $True }
      "^10"                { $NetworkSummary.Class = "B" }
      "^00001010"          { $NetworkSummary.Class = "A"; $NetworkSummary.IsPrivate = $True }
      "^0"                 { $NetworkSummary.Class = "A" }
    }   

    Return $NetworkSummary
  }
}

Get-NetworkRange

And so does Get-NetworkRange.

Function Get-NetworkRange {
  <#
    .Synopsis
      Generates IP addresses within the specified network.
    .Description
      Get-NetworkRange finds the network and broadcast address as decimal values then starts a
      counter between the two, returning Net.IPAddress for each.
    .Parameter IPAddress
      Any IP address within the network range.
    .Parameter Network
      A network description in the format 1.2.3.4/24
    .Parameter SubnetMask
      The subnet mask for the network.
  #>

  [CmdLetBinding(DefaultParameterSetName = "IPAndMask")]
  Param(
    [Parameter(Mandatory = $True, Position = 0, ParameterSetName = "IPAndMask", ValueFromPipeline = $True)]
    [Net.IPAddress]$IPAddress, 

    [Parameter(Mandatory = $True, Position = 1, ParameterSetName = "IPAndMask")]
    [Alias("Mask")]
    [Net.IPAddress]$SubnetMask,

    [Parameter(Mandatory = $True, ParameterSetName = "CIDRNotation", ValueFromPipeline = $True)]
    [ValidatePattern('^(\d{1,3}\.){3}\d{1,3}[\\/]\d{1,2}$')]
    [String]$Network
  )

  Process {
    If ($PsCmdLet.ParameterSetName -eq 'CIDRNotation') {
      $Temp = $Network.Split("\/")
      $IPAddress = $Temp[0]
      $SubnetMask = ConvertTo-Mask $Temp[1]
    }

    $DecimalIP = ConvertTo-DecimalIP $IPAddress
    $DecimalMask = ConvertTo-DecimalIP $SubnetMask

    $DecimalNetwork = $DecimalIP -BAnd $DecimalMask
    $DecimalBroadcast = $DecimalIP -BOr ((-BNot $DecimalMask) -BAnd [UInt32]::MaxValue)

    For ($i = $($DecimalNetwork + 1); $i -lt $DecimalBroadcast; $i++) {
      ConvertTo-DottedDecimalIP $i
    }
  }
}

Get-Subnets

I ran into a need to calculate a list of subnets of a specific length within a super-net, this function does just that.

Function Get-Subnets {
  <#
    .Synopsis
      Generates a list of subnets for a given network range
    .Description
      Generates a list of subnets for a given network range using either the address class or a
      user-specified value.
    .Parameter NetworkAddress
      Any address in the supernet range.
    .Parameter SubnetMask
      The desired mask, determines the size of the resulting subnet. Must be a valid subnet mask.
    .Parameter SupernetLength
      By default Get-Subnets uses the address class to determine the size of the supernet. Where the
      supernet describes the range of addresses being split.
  #>

  [CmdLetBinding(DefaultParameterSetName = "PS1")]
  Param(
    [Parameter(Mandatory = $True, Position = 0, ParameterSetName = "IPAndMask", ValueFromPipeline = $True)]
    [Net.IPAddress]$IPAddress, 

    [Parameter(Mandatory = $True, Position = 1, ParameterSetName = "IPAndMask")]
    [Alias("Mask")]
    [Net.IPAddress]$SubnetMask,

    [Parameter(Mandatory = $True, ParameterSetName = "CIDRNotation", ValueFromPipeline = $True)]
    [ValidatePattern('^(\d{1,3}\.){3}\d{1,3}[\\/]\d{1,2}$')]
    [String]$Network,

    [ValidateRange(1, 32)]
    [UInt32]$SupernetLength
  )

  Process {
    If ($PsCmdLet.ParameterSetName -eq 'CIDRNotation') {
      $Temp = $Network.Split("\/")
      $IPAddress = $Temp[0]
      $SubnetMask = ConvertTo-Mask $Temp[1]
    } Else {
      $SubnetLength = ConvertTo-MaskLength $SubnetMask
    }

    If (!$SupernetLength) {
      $SupernetLength = Switch -RegEx ($(ConvertTo-BinaryIP $IPAddress)) {
        "^110"  { 24 }
        "^10"   { 16 }
        "^0"    { 8 }
        default { 24 }
      }
    }
    If ($SupernetLength -gt $SubnetLength) {
      Write-Error "Subnet is larger than supernet. Aborting"
    }
    $SupernetMask = ConvertTo-Mask $SupernetLength

    $NumberOfNets = [Math]::Pow(2, ($SubnetLength - $SupernetLength))
    $NumberOfAddresses = [Math]::Pow(2, (32 - $SubnetLength))

    $SupernetAddress = Get-NetworkAddress $IPAddress $SupernetMask
    $DecimalAddress = ConvertTo-DecimalIP $SupernetAddress

    For ($i = 0; $i -lt $NumberOfNets; $i++) {
      $NetworkAddress = ConvertTo-DottedDecimalIP $DecimalAddress 

      "" | Select-Object @{n='NetworkAddress';e={ $NetworkAddress }},
        @{n='BroadcastAddress';e={ Get-BroadcastAddress $NetworkAddress $SubnetMask }},
        @{n='SubnetMask';e={ $SubnetMask }},
        @{n='HostAddresses';e={
          $NumberOfHosts = $NumberOfAddresses - 2
          If ($NumberOfHosts -lt 0) { 0 } Else { $NumberOfHosts } }}

      $DecimalAddress += $NumberOfAddresses
    }
  }
}

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NetShell

Chris — Thu, 25 Nov 2010 19:56:50 +0000

It’s been a while since I’ve posted, and since it’s almost Christmas I thought I’d better get on with it.

Without further ado I want to post NetShell (I’m not very good at coming up with imaginative names). NetShell is a collection of 17 functions and a few supporting functions in a script module.

Download NetShell

Installation is a manual process, but not too hard. Open up Documents\WindowsPowerShell\Modules, extract the ZIP file. Make sure it includes the NetShell folder or it won’t work. The module is not currently signed, something else on the to-do list. Once it’s there, Import-Module NetShell and off you go.

It includes the following:

ConvertTo-BinaryIP	Converts an IP address into a binary string
ConvertTo-Byte	A supporting function, a simple conversion of a string to a byte array (ASCII encoding)
ConvertTo-DecimalIP	Converts an IP address to 32-bit decimal number
ConvertTo-DottedDecimalIP	Converts a binary or 32-bit decimal back to an IP
ConvertTo-Mask	Converts from a mask length. For example, gets you from 22 to 255.255.252.0
ConvertTo-MaskLength	Converts from the IP form of a mask to the length
ConvertTo-String	Another supporting function, converts a byte array to a string (ASCII encoding)
Get-BroadcastAddress	Returns the broadcast address for the specified IP address and subnet mask
Get-NetworkAddress	Returns the network address for the specified IP address and subnet mask
Get-NetworkRange	Returns every IP within the specified range
Get-NetworkSummary	Everything about an IP address and mask I considered useful
New-DhcpDiscoverPacket	A supporting function for Send-DhcpDiscover. Creates the packet to send (a large byte array)
New-Socket	Creates an instance of System.Net.Sockets.Socket, an arbitrary network socket to do with as you please.
New-SysLogDateTime	A supporting function to create a DateTime string in the format SysLog likes.
Read-DhcpOption	A supporting function to read off an Option from a DHCP packet. Needs to be fed the Extended.BinaryReader class at the top of the module.
Read-DhcpPacket	Creates and uses an instance of Extended.BinaryReader to process a DHCP packet and translate the fields.
Receive-Bytes	Receives a stream of bytes from the network using a socket
Remove-Socket	Cleans up after New-Socket
Send-Bytes	Sends an arbitrary byte array over the network using a socket
Send-DhcpDiscover	Creates and sends a DHCPDISCOVER packet, then processes and returns the response
Start-Syslog	Starts a SysLog server. No termination for this one at the moment. Needs a bit more work.
Test-Smtp	Does the SMTP test you normally wind up doing with telnet, returning all the results along with the SMTP banner.
Test-SysLogDateTime	A supporting function to check the format of a DateTime that may or may not be present in a SysLog message.
Test-SysLogPRI	A supporting function to test of the PRI value in a SysLog message.
Test-TcpPort	Returns a boolean indicating whether or not the port connection succeeded.

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VbScript: GetADSubnets

Chris — Sat, 25 Oct 2008 10:46:37 +0000

The VbScript below demonstrates how subnet information might be retrieved from Active Directory. It is possible to use a search using to return this information (for objectClass=subnet). This method connects to the subnets container and loops through the contents returning the network address and mask length in a Dictionary object.

Function GetADSubnets
  ' Return Type: Array

  Dim objRootDSE : Set objRootDSE = GetObject("LDAP://RootDSE")
  Dim objSubnets : Set objSubnets = GetObject("LDAP://CN=Subnets,CN=Sites," & _
    objRootDSE.GEt("configurationNamingContext"))

  Dim arrSubnets() : Dim i : i = 0
  For Each objSubnet in objSubnets
    ReDim Preserve arrSubnets(i)
    arrSubnets(i) = objSubnet.Get("name")
    i = i + 1
  Next

  GetADSubnets = arrSubnets
End Function

Usage example

WScript.Echo Join(GetADSubnets, vbCrlf)

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