How to convert IP number to IPV6 using PowerShell?

Question

I have CSV containing IP number's related to IPv6 and I am reading and converting them to IPv6 ip address which is failing at the moment.

I am using below code but getting error:

Cannot convert value "281470698520576" to type "System.Net.IPAddress". Error: "Specified argument was out of the range of valid values.

function Convert-NumberToIP
{
    param(
        [Parameter(Mandatory=$true)][string]$number
    )

    [Int64] $numberInt = 0
    
    if([Int64]::TryParse($number, [ref]$numberInt))
    {
        if(($numberInt -ge 0) -and ($numberInt -le 0xFFFFFFFFl))
        {
            #([IPAddress] $numberInt).ToString()
            $ipBytes = ([IPAddress]$numberInt).GetAddressBytes()
            [array]::Reverse($ipBytes)
            ([IPAddress]$ipBytes).IPAddressToString
        }
    }
}

$startIP = Convert-NumberToIP -number '281470698520576'
$endIP = Convert-NumberToIP -number '281470698520580'

Answer 1

To use a 128bit integer in PowerShell you can leverage .NET System.Numerics.BigInteger class. Like this:

$ipv6Decimal = [System.Numerics.BigInteger]::Parse($number)

Then you can convert the BigInt to a byte array using ToByteArray(). However the resulting array needs to be "padded" to 16 bytes and reversed (Host vs Network order).

This works for me:

function Convert-NumberToIPv6
{
    param(
        [Parameter(Mandatory=$true)][string]$number
    )
     
    $ipv6Decimal  = [System.Numerics.BigInteger]::Parse($number)
    $ipv6Bytes = $ipv6Decimal.ToByteArray()
    # pad to 16 bytes
    [Array]::Resize([ref]$ipv6Bytes, 16)

    # reverse the bytes
    [Array]::Reverse($ipv6Bytes)
    
    # provide a scope identifier to prevent "cannot find overload error"
    $ipAddress = New-Object Net.IPAddress($ipv6Bytes, 0)
    $ipAddress.ToString()
}

So the output for: Convert-NumberToIPv6 -number '281470698520576' is ::ffff:1.0.0.0

Answer 2

Using PowerShell 7+, here is a possible implementation that works similar to the function in your question in that invalid input will be detected and doesn't cause an exception. In this case the function returns "nothing", which converts to $false in a boolean context.

If you need compatibility with Windows PowerShell (5.x), have a look at this answer.

function Convert-NumberToIPv6
{
    param(
        [Parameter(Mandatory)] [string] $number
    )

    [Numerics.BigInteger] $bigInt = 0
    if( [Numerics.BigInteger]::TryParse( $number, [ref] $bigInt ) ) {
        # Check that input is in the range of an unsigned 128 bit number
        if( $bigInt.Sign -ge 0 -and $bigInt.GetBitLength() -le 128 ) {
            $bytes = $bigInt.ToByteArray($true, $true)  # unsigned, big-endian
            $zeros = @(0) * (16 - $bytes.Length)        # zeros to preprend to ensure 128 bit length
            $bytes = [byte[]] ($zeros + $bytes)         # prepend zeros
            ([IPAddress] $bytes).ToString()             # convert to IPAddress and then to string
        }
    }
}

Usage:

if( $ipv6 = Convert-NumberToIPv6 '281470698520576' ) {
    # Conversion successful, output the address in text form
    $ipv6   
}
else {
    "IPv6 conversion failed!"
}

Output:

::ffff:1.0.0.0