VNet.psm1
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<# .SYNOPSIS List subnets for a VNet and show any unallocated gaps .EXAMPLE Find-FreeSubnets.ps1 -ResourceGroup rg-myapp-prod-westus-001 -VNetName vnet-myapp-prod-westus-001 #> function Find-FreeSubnets { [CmdletBinding()] param ( [string] $ResourceGroup, [string] $VNetName ) begin { # https://gist.github.com/davidjenni/7eb707e60316cdd97549b37ca95fbe93 function cidrToIpRange { param ( [string] $cidrNotation ) $addr, $maskLength = $cidrNotation -split '/' [int]$maskLen = 0 if (-not [int32]::TryParse($maskLength, [ref] $maskLen)) { throw "Cannot parse CIDR mask length string: '$maskLen'" } if (0 -gt $maskLen -or $maskLen -gt 32) { throw "CIDR mask length must be between 0 and 32" } $ipAddr = [Net.IPAddress]::Parse($addr) if ($ipAddr -eq $null) { throw "Cannot parse IP address: $addr" } if ($ipAddr.AddressFamily -ne [Net.Sockets.AddressFamily]::InterNetwork) { throw "Can only process CIDR for IPv4" } $shiftCnt = 32 - $maskLen $mask = -bnot ((1 -shl $shiftCnt) - 1) $ipNum = [Net.IPAddress]::NetworkToHostOrder([BitConverter]::ToInt32($ipAddr.GetAddressBytes(), 0)) $ipStart = ($ipNum -band $mask) $ipEnd = ($ipNum -bor (-bnot $mask)) # return as tuple of strings: #([BitConverter]::GetBytes([Net.IPAddress]::HostToNetworkOrder($ipStart)) | ForEach-Object { $_ } ) -join '.' $bytes = [BitConverter]::GetBytes([Net.IPAddress]::HostToNetworkOrder($ipStart)) New-Object -TypeName "Net.IPAddress" -argumentList (, $bytes) #([BitConverter]::GetBytes([Net.IPAddress]::HostToNetworkOrder($ipEnd)) | ForEach-Object { $_ } ) -join '.' $bytes = [BitConverter]::GetBytes([Net.IPAddress]::HostToNetworkOrder($ipEnd)) New-Object Net.IPAddress -ArgumentList (, $bytes) } $vnet = Get-AzVirtualNetwork -Name $VNetName -ResourceGroupName $ResourceGroup $vnetStart, $vnetEnd = cidrToIpRange $vnet.AddressSpace.AddressPrefixes "VNET $vnetStart - $vnetEnd" $sorted = $vnet.Subnets.AddressPrefix | Sort-Object -Property { $addr, $maskLength = $_ -split '/' $ip = ([Net.IPAddress] $addr) $ipNum = [Net.IPAddress]::NetworkToHostOrder([BitConverter]::ToInt32($ip.GetAddressBytes(), 0)) $ipNum } $maskToAddresses = @{ 28 = 16; 27 = 32; 26 = 64; 25 = 128 } $addressToStarts = @{ } $maskToAddresses.Values | ForEach-Object { $addressToStarts.Add($_, $(for ($i = 0; $i -lt 255; $i += $_) { $i })) } $nextAvailableNum = 0 $notFirst = $false foreach ($cidr in $sorted) { $start, $end = cidrToIpRange $cidr $startNum = [Net.IPAddress]::NetworkToHostOrder([BitConverter]::ToInt32($start.GetAddressBytes(), 0)) if ($notFirst -and $nextAvailableNum -ne $startNum ) { $bytes = [BitConverter]::GetBytes([Net.IPAddress]::HostToNetworkOrder($nextAvailableNum)) $nextAvailable = New-Object Net.IPAddress -ArgumentList (, $bytes) "Free block(s) of $($startNum - $nextAvailableNum) starting at $nextAvailable" for ($i = $nextAvailableNum; $i -lt $startNum; $i += 8) { $bytes = [BitConverter]::GetBytes([Net.IPAddress]::HostToNetworkOrder($i)) $freeIp = New-Object Net.IPAddress -ArgumentList (, $bytes) foreach ($mask in $maskToAddresses.Keys) { $address = $maskToAddresses[$mask] if ($addressToStarts[$address] -contains $bytes[3] ) { $freeCidr = $freeIp.IPAddressToString + "/$mask" # Check this doesn't overlap next $possibleFreeStart, $possibleFreeEnd = cidrToIpRange $freeCidr $possibleFreeEndNum = [Net.IPAddress]::NetworkToHostOrder([BitConverter]::ToInt32($possibleFreeEnd.GetAddressBytes(), 0)) if ($possibleFreeEndNum -lt $startNum) { " " + $freeCidr } } } } } $notFirst = $true "{0,18} : {1,15} - {2,15}" -f $cidr, $start, $end $nextAvailableNum = [Net.IPAddress]::NetworkToHostOrder([BitConverter]::ToInt32($end.GetAddressBytes(), 0)) + 1 $bytes = [BitConverter]::GetBytes([Net.IPAddress]::HostToNetworkOrder($ipEnd)) } if ($end -ne $vnetEnd) { $bytes = [BitConverter]::GetBytes([Net.IPAddress]::HostToNetworkOrder($nextAvailableNum)) $nextAvailable = New-Object Net.IPAddress -ArgumentList (, $bytes) "Free block(s) starting at $nextAvailable" } } } |