VNet.psm1
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class Subnet { [string] $CIDR [NET.IPAddress] $Start [NET.IPAddress] $End [string] ToString() { return $this.CIDR } } class Free { [NET.IPAddress] $Start [NET.IPAddress] $End [int] $Size [string[]] $CIDRAvailable [string] ToString() { return $this.Size } } class VNetSummary { [string] $VNetStart [string] $VNetEnd [free[]] $Available [subnet[]] $Subnets } <# .SYNOPSIS List subnets for a VNet and show any unallocated gaps .DESCRIPTION Returns a list of subnets in use for a particular VNET and also any gaps available .PARAMETER ResourceGroup The name of the resource group that contains a virtual network .PARAMETER VNetName The name of the virtual network to query for subnets .NOTES This function uses Azure PowerShell cmdlets, so assumes that you've already run Connect-AzAccount to sign in to Azure. .EXAMPLE $result = Find-FreeSubnets -ResourceGroup rg-freesubnet-australiaeast -VNetName vnet-freesubnet-australiaeast Displaying $result: VNet Start VNet End Available Subnets ---------- -------- --------- ------- 10.0.0.0 10.0.255.255 {48, 8} {10.0.0.0/24, 10.0.1.0/28, 10.0.1.64/28, 10.0.1.88/29} And the 'Available' property contains: Start End Size Available ranges ----- --- ---- ---------------- 10.0.1.16 10.0.1.63 48 {10.0.1.16/28, 10.0.1.32/27, 10.0.1.32/28, 10.0.1.48/28} 10.0.1.80 10.0.1.87 8 The 'Available ranges' array is a list of one or more CIDR ranges that could utilise the available IP addresses. #> function Find-FreeSubnets { [CmdletBinding()] [OutputType([VNetSummary])] 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: $bytes = [BitConverter]::GetBytes([Net.IPAddress]::HostToNetworkOrder($ipStart)) New-Object -TypeName "Net.IPAddress" -argumentList (, $bytes) $bytes = [BitConverter]::GetBytes([Net.IPAddress]::HostToNetworkOrder($ipEnd)) New-Object Net.IPAddress -ArgumentList (, $bytes) } $vnet = Get-AzVirtualNetwork -Name $VNetName -ResourceGroupName $ResourceGroup [Net.IPAddress] $vnetStart, [Net.IPAddress] $vnetEnd = cidrToIpRange $vnet.AddressSpace.AddressPrefixes $result = [VNetSummary]::new() $result.VNetStart = $vnetStart $result.VNetEnd = $vnetEnd # Create fake subnet immediately following the end of the VNet $ipNum = [Net.IPAddress]::NetworkToHostOrder([BitConverter]::ToInt32($vnetEnd.GetAddressBytes(), 0)) + 1 $bytes = [BitConverter]::GetBytes([Net.IPAddress]::HostToNetworkOrder($ipNum)) [Net.IPAddress] $afterLastAvailable = New-Object Net.IPAddress -ArgumentList (, $bytes) $afterLastAvailableCidr = "$afterLastAvailable/31" $sorted = @($vnet.Subnets.AddressPrefix) + $afterLastAvailableCidr | 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) $bytes = [BitConverter]::GetBytes([Net.IPAddress]::HostToNetworkOrder($startNum-1)) $lastAvailable = New-Object Net.IPAddress -ArgumentList (, $bytes) $free = [Free]::new() $free.Start = $nextAvailable $free.End = $lastAvailable $free.Size = $startNum - $nextAvailableNum $result.Available += $free for ($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 | Sort-Object)) { $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) { $free.CIDRAvailable += $freeCidr } } } } } $notFirst = $true if ($cidr -ne $afterLastAvailableCidr) { $subnet = [Subnet]::new() $subnet.CIDR = $cidr $subnet.Start = $start $subnet.End = $end $result.Subnets += $subnet } $nextAvailableNum = [Net.IPAddress]::NetworkToHostOrder([BitConverter]::ToInt32($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) } $result } } |