VNet.psm1
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class Subnet { [string] $CIDR [NET.IPAddress] $Start [NET.IPAddress] $End [string] ToString() { return $this.CIDR } } class VNetRange { [NET.IPAddress] $Start [NET.IPAddress] $End [string] ToString() { return $this.Start + "-" + $this.End } } class Free { [NET.IPAddress] $Start [NET.IPAddress] $End [int] $Size [string[]] $CIDRAvailable [string] ToString() { return $this.Size } } class VNetSummary { [string] $VNetStart [string] $VNetEnd [VNetRange[]] $VNetRanges [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} If the virtual network has multiple address ranges, VNetStart and VNetEnd are those of the last range. In that case, 'Available' and 'Subnets' contain all available ranges and all subnets of all address ranges. 'VNetRanges' contains the start and end of each address range in the virtual network. 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 $result = [VNetSummary]::new() $vnetAddressPrefixes = $vnet.AddressSpace.AddressPrefixes foreach($addressPrefix in $vnetAddressPrefixes) { [Net.IPAddress] $vnetStart, [Net.IPAddress] $vnetEnd = cidrToIpRange $addressPrefix $result.VNetStart = $vnetStart $result.VNetEnd = $vnetEnd $vnetRange = [VNetRange]::new() $vnetRange.Start = $vnetStart $vnetRange.End = $vnetEnd $result.VNetRanges += $vnetRange # 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" # create fake subnet immediately before the start of the VNet $ipNum = [Net.IPAddress]::NetworkToHostOrder([BitConverter]::ToInt32($vnetStart.GetAddressBytes(), 0)) - 1 $bytes = [BitConverter]::GetBytes([Net.IPAddress]::HostToNetworkOrder($ipNum)) [Net.IPAddress] $beforeFirstAvailable = New-Object Net.IPAddress -ArgumentList (, $bytes) $beforeFirstAvailableCidr = "$beforeFirstAvailable/31" $sorted = @($beforeFirstAvailableCidr) + @($vnet.Subnets.AddressPrefix) + @($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 -and $cidr -ne $beforeFirstAvailableCidr) { $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 } } |