SubnetTools.psm1
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function Find-ValidSubnet { <# .SYNOPSIS Takes an IPv4 network address and creates subnets based on hosts and networks needed .DESCRIPTION This command whill calculate all possible subnets for a given scenerio, given an orginal subnet and mask with the number of subnets required and the hosts per subnet. For each subnet it will show all of the valid subnet range values for example: Find-ValidSubnet -CIDRSubnetAddress 192.168.3.0/24 -AllSubnetsVLSM | ft -GroupBy mask Mask: 25 Mask SubnetID FirstValidIP LastValidIP BroadcastIP HostsPerSubnet Subnet TotalSubnets ---- -------- ------------ ----------- ----------- -------------- ------ ------------ 25 192.168.3.0 192.168.3.1 192.168.3.126 192.168.3.127 126 1 2 25 192.168.3.128 192.168.3.129 192.168.3.254 192.168.3.255 126 2 2 Mask: 26 Mask SubnetID FirstValidIP LastValidIP BroadcastIP HostsPerSubnet Subnet TotalSubnets ---- -------- ------------ ----------- ----------- -------------- ------ ------------ 26 192.168.3.0 192.168.3.1 192.168.3.62 192.168.3.63 62 1 4 26 192.168.3.64 192.168.3.65 192.168.3.126 192.168.3.127 62 2 4 26 192.168.3.128 192.168.3.129 192.168.3.190 192.168.3.191 62 3 4 26 192.168.3.192 192.168.3.193 192.168.3.254 192.168.3.255 62 4 4 It will also make sure the original network address is a network address and if it is not it will AND the given address with the oiginal mask to find the network address. It is suggested that the output be formated into a table with a -groupby Mask parameter. .EXAMPLE Find-ValidSubnet -CIDRSubnetAddress 192.168.0.0/16 -SubnetsRequired 4 -HostsPerSubnetRequired 4000 | Format-Table -GroupBy Mask Using the 192.168.0.0/16 network as a base this will find all subnet masks that will allow for a minimum of 4 subnets, while still allowing 4000 hosts per subnet. The subnets willl be listed for each subnet mask discovered .EXAMPLE Find-ValidSubnet -CIDRSubnetAddress 192.168.0.0/16 -AllSubnetsVLSM | Format-Table -GroupBy Mask Using the 192.168.0.0/16 network as a base this will find all subnets that are possible, this is very handy when trying to plan VLSM subnets. .PARAMETER CIDRSubnetAddress This parameter requires the network address to be entered with the CIDR mask as well. In this format 192.168.0.0/16 .PARAMETER SubnetsRequired This parameter declares how many subnets the CIDR network will need to be broken into as a minimum. Because this is a minimum, this command will also look for all valid subnets as long as it still allows for the number of hosts per subnet, -HostsPerSubnetRequired parameter value. .PARAMETER HostsPerSubnetRequired This parameter dictates the minimum amount of hosts that are required per subnet. .PARAMETER SmallestSubnets This parameter only shows the smallest subnets, those with the bigest subnet mask. .PARAMETER AllSubnetsVLSM This parameter show all possible subnets which can be very handy when planning VLSM subnets. .NOTES General notes Created by: Brent Denny Created on: 09 Mar 2021 Last Modified: 15 Mar 2021 #> [cmdletbinding(DefaultParameterSetName='Default',PositionalBinding=$false)] Param ( [Parameter(Mandatory=$true,ParameterSetName='VLSM')] [Parameter(ParameterSetName='Subnet')] [string]$CIDRSubnetAddress, [Parameter(Mandatory=$true,ParameterSetName='Subnet')] [int]$SubnetsRequired, [Parameter(Mandatory=$true,ParameterSetName='Subnet')] [int]$HostsPerSubnetRequired, [Parameter(ParameterSetName='Subnet')] [switch]$SmallestSubnets, [Parameter(ParameterSetName='VLSM')] [switch]$AllSubnetsVLSM ) function ConvertTo-IPAddressObject { [cmdletbinding(DefaultParameterSetName='Default')] Param ( [int]$BitCount, [Parameter(ParameterSetName='IPAddress')] [string]$IPAddress, [Parameter(ParameterSetName='DecAddress')] [int64]$DecAddress ) # this function will take a bit count, IPaddress or decimal address, and # convert any of them into an object that contains a forward and reverse versions # of the IPAddresses and their decimal values if ($PSCmdlet.ParameterSetName -eq 'Default') { $BinaryString = '1' * $BitCount + '0' * (32 - $BitCount) $IPObj = [ipaddress]([convert]::ToInt64($BinaryString,2)) $FwdAddrIPObj = [ipaddress]($IPObj.IPAddressToString -replace '^(\d+)\.(\d+)\.(\d+)\.(\d+)$','$4.$3.$2.$1') $RevAddrIPObj = $IPObj } elseif ($PSCmdlet.ParameterSetName -eq 'IPAddress') { $FwdAddrIPObj = [ipaddress]$IPAddress $RevAddrIPObj = [ipaddress]($IPAddress -replace '^(\d+)\.(\d+)\.(\d+)\.(\d+)$','$4.$3.$2.$1') } elseif ($PSCmdlet.ParameterSetName -eq 'DecAddress') { $IPObj = [ipaddress]$DecAddress $FwdAddrIPObj = [ipaddress]($IPObj.IPAddressToString -replace '^(\d+)\.(\d+)\.(\d+)\.(\d+)$','$4.$3.$2.$1') $RevAddrIPObj = $IPObj } $ObjProp = [ordered]@{ FwdAddrIP = $FwdAddrIPObj.IPAddressToString FwdAddrDec = $FwdAddrIPObj.Address RevAddrIP = $RevAddrIPObj.IPAddressToString RevAddrDec = $RevAddrIPObj.Address } New-object -TypeName psobject -Property $ObjProp } function Find-IPSubnetRange { [cmdletbinding()] Param ( [string]$IPAddress, [int]$InitialMask, [int]$SubnetMask ) # This function will find all of the valid subnets for a subnetted mask, and list the following # Mask,Subnet,FirstValidIP,LastValidIP,BroadcastIP,HostsPerSubnet and Subnet Number $MaxSubnetIndex = [math]::Pow(2,$SubnetMask - $InitialMask) - 1 $JumpValue = [math]::Pow(2,8-$SubnetMask % 8) $JumpIndex = [math]::Truncate($SubnetMask / 8) if ($JumpValue -eq 256) { $JumpValue = 1 $JumpIndex = $JumpIndex - 1 } [int[]]$JumpIPArray = 0,0,0,0 $JumpIPArray[$JumpIndex] = $JumpValue $JumpIPAddr = $JumpIPArray -join '.' $JumpIPAddressSet = ConvertTo-IPAddressObject -IPAddress $JumpIPAddr $IPAddressSet = ConvertTo-IPAddressObject -IPAddress $IPAddress foreach ($SubnetIndex in (0..$MaxSubnetIndex)) { # The ...RevDec refers to the IP addresses decimal value, it 'turns out' that the # [IPAddress] object reverses the decimal value of the IP, so by reversing the # reverse we get the actual decimal value. This is why you see this everywhere # within this function $ThisSubnetRevDec = $IPAddressSet.RevAddrDec + ($SubnetIndex * $JumpIPAddressSet.RevAddrDec) $ThisSubnetSet = ConvertTo-IPAddressObject -DecAddress $ThisSubnetRevDec $FirstValidRevDec = $ThisSubnetRevDec + 1 $LastValidRevDec = $ThisSubnetRevDec + $JumpIPAddressSet.RevAddrDec - 2 $BroadCastRevDec = $ThisSubnetRevDec + $JumpIPAddressSet.RevAddrDec - 1 $FirstValidSet = ConvertTo-IPAddressObject -DecAddress $FirstValidRevDec $LastValidSet = ConvertTo-IPAddressObject -DecAddress $LastValidRevDec $BroadCastSet = ConvertTo-IPAddressObject -DecAddress $BroadCastRevDec $ObjProp = [ordered]@{ Mask = $SubnetMask SubnetID = $ThisSubnetSet.FwdAddrIP FirstValidIP = $FirstValidSet.FwdAddrIP LastValidIP = $LastValidSet.FwdAddrIP BroadcastIP = $BroadCastSet.FwdAddrIP HostsPerSubnet = [math]::Pow(2,32 -$SubnetMask) - 2 Subnet = $SubnetIndex + 1 TotalSubnets = $MaxSubnetIndex + 1 } New-Object -TypeName psobject -Property $ObjProp } } ## MAIN Function BODY if ($AllSubnetsVLSM -eq $true) { $SubnetsRequired = 1 $HostsPerSubnetRequired = 1 } $CIDRParts = $CIDRSubnetAddress -split '\/' $SubnetID = $CIDRParts[0] -as [string] $InitialMask = $CIDRParts[1] -as [int] $HostBitsRequired = [math]::Ceiling([math]::Log($HostsPerSubnetRequired+2)/[math]::log(2)) # +2 to cater for NetworkId and BroadcastID addresses $NetworkBitsRequired = [math]::Floor([math]::Log($SubnetsRequired)/[math]::log(2)) $TotalBitsRequired = $InitialMask + $HostBitsRequired + $NetworkBitsRequired # Make sure the given IP addres is an IP Address if ($CIDRSubnetAddress -notmatch '^([1-9]|[1-9][0-9]|1[01][0-9]|12[0-6]|12[89]|1[3-9][0-9]|2[0-2][0-3])(\.([0-9]|[1-9][0-9]|1[0-9][0-9]|2[0-4][0-9]|25[0-5])){3}\/([2-9]|[12][0-9]|30)$') { write-warning "$CIDRSubnetAddress - is not a valid address please enter the address and mask, for example: 164.12.0.0/16" break } elseif ($TotalBitsRequired -gt 32) { Write-Warning "The solution you requested requires $TotalBitsRequired bits in the address, we only have 32 bits in IPv4" break } else { $MaskSet = ConvertTo-IPAddressObject -BitCount $InitialMask $SubnetSet = ConvertTo-IPAddressObject -IPAddress $SubnetID # ANDing the Network address with original mask to produce a real network address # this is just in case an address that was entered was a host address and # not the network address. $NetBinAndMaskDec = $SubnetSet.RevAddrDec -band $MaskSet.RevAddrDec # Fixed IP uses ANDing to make sure the subnet address is the actual address of the subnet and not a host address # the subnet. $ActualNetworkAddrSet = ConvertTo-IPAddressObject -DecAddress $NetBinAndMaskDec $SubnetingBitsArray = 0..(32 - $TotalBitsRequired ) | ForEach-Object { # Finding how many subnet bits are required for the number of subnets requested [math]::Ceiling([math]::Log($SubnetsRequired)/[math]::log(2)) + $_ + $InitialMask } $SubnetResults = foreach ($SubnettedBits in $SubnetingBitsArray) { # Go find the valid subnet ranges per valid subnet mask Find-IPSubnetRange -IPAddress $ActualNetworkAddrSet.FwdAddrIP -InitialMask $InitialMask -SubnetMask $SubnettedBits } if ($SmallestSubnets -eq $false) {$SubnetResults} else {$SubnetResults | Where-Object {$_.Mask -eq $SubnetResults[-1].Mask}} } } |