function Invoke-ReverseDnsLookup
{
<#
.SYNOPSIS

Perform a reverse DNS lookup scan on a range of IP addresses.

PowerSploit Function: Invoke-ReverseDnsLookup  
Author: Matthew Graeber (@mattifestation)  
License: BSD 3-Clause  
Required Dependencies: None  
Optional Dependencies: None  

.DESCRIPTION

Invoke-ReverseDnsLookup scans an IP address range for DNS PTR records. This script is useful for performing DNS reconnaissance prior to conducting an authorized penetration test.

.PARAMETER IPRange

Specifies the IP address range. The range provided can be in the form of a single IP address, a low-high range, or a CIDR range. Comma-delimited ranges may can be provided.

.EXAMPLE

Invoke-ReverseDnsLookup 74.125.228.0/29

IP              HostName
--              --------
74.125.228.1    iad23s05-in-f1.1e100.net
74.125.228.2    iad23s05-in-f2.1e100.net
74.125.228.3    iad23s05-in-f3.1e100.net
74.125.228.4    iad23s05-in-f4.1e100.net
74.125.228.5    iad23s05-in-f5.1e100.net
74.125.228.6    iad23s05-in-f6.1e100.net

Description
-----------
Returns the hostnames of the IP addresses specified by the CIDR range.

.EXAMPLE

Invoke-ReverseDnsLookup '74.125.228.1,74.125.228.4-74.125.228.6'

IP              HostName
--              --------
74.125.228.1    iad23s05-in-f1.1e100.net
74.125.228.4    iad23s05-in-f4.1e100.net
74.125.228.5    iad23s05-in-f5.1e100.net
74.125.228.6    iad23s05-in-f6.1e100.net

Description
-----------
Returns the hostnames of the IP addresses specified by the IP range specified.

.EXAMPLE

Write-Output "74.125.228.1,74.125.228.0/29" | Invoke-ReverseDnsLookup

IP                                                          HostName
--                                                          --------
74.125.228.1                                                iad23s05-in-f1.1e100.net
74.125.228.1                                                iad23s05-in-f1.1e100.net
74.125.228.2                                                iad23s05-in-f2.1e100.net
74.125.228.3                                                iad23s05-in-f3.1e100.net
74.125.228.4                                                iad23s05-in-f4.1e100.net
74.125.228.5                                                iad23s05-in-f5.1e100.net
74.125.228.6                                                iad23s05-in-f6.1e100.net

Description
-----------
Returns the hostnames of the IP addresses piped from another source.

.LINK

http://www.exploit-monday.com
https://github.com/mattifestation/PowerSploit
#>

    [Diagnostics.CodeAnalysis.SuppressMessageAttribute('PSShouldProcess', '')]
    [Diagnostics.CodeAnalysis.SuppressMessageAttribute('PSUseApprovedVerbs', '')]
    [CmdletBinding()]
    Param (
        [Parameter(Position = 0, Mandatory = $True,ValueFromPipeline=$True)]
        [String]
        $IpRange
    )

    BEGIN {

        function Parse-IPList ([String] $IpRange)
        {

            function IPtoInt
            {
                Param([String] $IpString)

                $Hexstr = ""
                $Octets = $IpString.Split(".")
                foreach ($Octet in $Octets) {
                        $Hexstr += "{0:X2}" -f [Int] $Octet
                }
                return [Convert]::ToInt64($Hexstr, 16)
            }

            function InttoIP
            {
                Param([Int64] $IpInt)
                $Hexstr = $IpInt.ToString("X8")
                $IpStr = ""
                for ($i=0; $i -lt 8; $i += 2) {
                        $IpStr += [Convert]::ToInt64($Hexstr.SubString($i,2), 16)
                        $IpStr += '.'
                }
                return $IpStr.TrimEnd('.')
            }

            $Ip = [System.Net.IPAddress]::Parse("127.0.0.1")

            foreach ($Str in $IpRange.Split(","))
            {
                $Item = $Str.Trim()
                $Result = ""
                $IpRegex = "\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}"

                # First, validate the input
                switch -regex ($Item)
                {
                    "^$IpRegex/\d{1,2}$"
                    {
                        $Result = "cidrRange"
                        break
                    }
                    "^$IpRegex-$IpRegex$"
                    {
                        $Result = "range"
                        break
                    }
                    "^$IpRegex$"
                    {
                        $Result = "single"
                        break
                    }
                    default
                    {
                        Write-Warning "Improper input"
                        return
                    }
                }

                #Now, start processing the IP addresses
                switch ($Result)
                {
                    "cidrRange"
                    {
                        $CidrRange = $Item.Split("/")
                        $Network = $CidrRange[0]
                        $Mask = $CidrRange[1]

                        if (!([System.Net.IPAddress]::TryParse($Network, [ref] $Ip))) { Write-Warning "Invalid IP address supplied!"; return}
                        if (($Mask -lt 0) -or ($Mask -gt 30)) { Write-Warning "Invalid network mask! Acceptable values are 0-30"; return}

                        $BinaryIP = [Convert]::ToString((IPtoInt $Network),2).PadLeft(32,'0')
                        #Generate lower limit (Excluding network address)
                        $Lower = $BinaryIP.Substring(0, $Mask) + "0" * ((32-$Mask)-1) + "1"
                        #Generate upper limit (Excluding broadcast address)
                        $Upper = $BinaryIP.Substring(0, $Mask) + "1" * ((32-$Mask)-1) + "0"
                        $LowerInt = [Convert]::ToInt64($Lower, 2)
                        $UpperInt = [Convert]::ToInt64($Upper, 2)
                        for ($i = $LowerInt; $i -le $UpperInt; $i++) { InttoIP $i }
                    }
                    "range"
                    {
                        $Range = $item.Split("-")

                        if ([System.Net.IPAddress]::TryParse($Range[0],[ref]$Ip)) { $Temp1 = $Ip }
                        else { Write-Warning "Invalid IP address supplied!"; return }

                        if ([System.Net.IPAddress]::TryParse($Range[1],[ref]$Ip)) { $Temp2 = $Ip }
                        else { Write-Warning "Invalid IP address supplied!"; return }

                        $Left = (IPtoInt $Temp1.ToString())
                        $Right = (IPtoInt $Temp2.ToString())

                        if ($Right -gt $Left) {
                            for ($i = $Left; $i -le $Right; $i++) { InttoIP $i }
                        }
                        else { Write-Warning "Invalid IP range. The right portion must be greater than the left portion."; return}

                        break
                    }
                    "single"
                    {
                        if ([System.Net.IPAddress]::TryParse($Item,[ref]$Ip)) { $Ip.IPAddressToString }
                        else { Write-Warning "Invalid IP address supplied!"; return }
                        break
                    }
                    default
                    {
                        Write-Warning "An error occurred."
                        return
                    }
                }
            }
        }
    }

    PROCESS {
        Parse-IPList $IpRange | ForEach-Object {
            try {
                Write-Verbose "Resolving $_"
                $Temp = [System.Net.Dns]::GetHostEntry($_)

                $Result = @{
                    IP = $_
                    HostName = $Temp.HostName
                }

                New-Object PSObject -Property $Result
            }
            catch [System.Net.Sockets.SocketException] {
                Write-Verbose "Error: $_"
            }
        }
    }
}