Find Duplicate DNS entries

##
## build-dns-objects.ps1
##

##
## Michael B. Smith
## michael (at) TheEssentialExchange.com
## April, 2012
##
## Patched 2016-02-03
## If a computer had multiple IP addresses, the scanner would get confused and
## not properly populate the $objects array.
##

##
## Primary functionality:
##
## Based on either an input file or the output of a default command:
##
##  dnscmd ( $env:LogonServer ).SubString( 2 ) /enumrecords $env:UserDnsDomain "@"
##
## Create an array containing all of the DNS objects describing the input.
##
## ----
##
## Secondary functionality:
##
## Find all the duplicate IP addresses and the duplicate names 
## contained within either the file or the command output.
##
## By specifying the -skipRoot option, all records for the root of
## the domain are ignored.
##

##
## General record format returned by DNScmd.exe:
##
## name
## [aging:xxxxxxxx] 
## TTL
## resource-record-type
## value
## [optional additional values]
##
## Fields may be separated by one-or-more spaces or one-or-more tabs
## [aging:xxxxxxxx] fields are optional
##

[CmdletBinding(SupportsShouldProcess=$false, ConfirmImpact='None')]

Param(
 [string]$filename,
 [switch]$skipRoot=$true
)

Set-StrictMode -Version 2.0

function new-dns-object
{
 return ( "" | Select Name, Aging, TTL, RRtype, Value )
}

function tmpFileName
{
 [string] $strFile = ( Join-Path $Env:Temp ( Get-Random ) ) + ".txt"
 Write-Verbose "tmpFileName $strFile"

 if( ( Test-Path -Path $strFile -PathType Leaf ) )
 {
  rm $strNetworkFile -EA 0
  if( $? )
  {
  ## write-output "...file was deleted"
  }
  else
  {
  ## write-output "...couldn't delete file, error: $($error[0].ToString())"
  }
 }

 return $strFile
}

# verify dnscmd.exe exists locally before running the script
If (! (Test-Path (Join-Path (Split-Path $env:comspec) "dnscmd.exe") )) {
    Write-Host "dnscmd.exe does not exist on this computer. The script cannot continue."
    Exit 1
} Else {

    if( $filename -and ( $filename.Length -gt 0 ) )
    {
     $tmp = $filename
    }
    else
    {
     $tmp = tmpFileName
     dnscmd ( $env:LogonServer ).SubString( 2 ) /enumrecords $env:UserDnsDomain "@" >$tmp
    }

    $objects = @()
    $records = gc $tmp
    Write-Verbose "records = $( $records.Count )"

    $priorName = ''

    ## Primary functionality:

    foreach( $record in $records )
    {
     ## Write-Debug "Processing: $record"

     if( !$record )
     {
      continue
     }
     if( $record -eq "Returned records:" )
     {
      continue
     }
     if( $record -eq "Command completed successfully." )
     {
      continue
     }

     if( $record -match "SOA" )
     {
      continue
     }

     $firstChar = $record.SubString( 0, 1 )
     $record = $record.Trim()

     if( $record.Length -eq 0 )
     {
      continue
     }

     $object = new-dns-object

     $index = 0

     $record = $record.Replace( "`t", " " )
     $record = $record.Replace( "  ", " " )
     $record = $record.Replace( "  ", " " )
     $record = $record.Replace( "  ", " " )
     Write-Debug "'$record'"

     $array = $record.Split( ' ' )
     Write-Debug "array contains $( $array.Count ) elements"
     if( $array.Count -gt 5 )
     {
      Write-Warning "This record has been parsed incorrectly: '$record'"
     }

     if( ( $firstchar -eq " " ) -or ( $firstchar -eq "`t" ) )
     {
      $object.Name = $priorName
      Write-Debug "Assigned priorName '$priorName'"
     }
     else
     {
      $object.Name = $array[ 0 ]
      $priorName   = $array[ 0 ]
      $index++
     }

     if(($array[$index].Length -ge 3) -and ($array[ $index ].SubString( 0, 3 ) -eq "[Ag"))  ## [Aging:3604987]
     {
      $object.Aging = $array[ $index ]
      $index++
     }
     
     $object.TTL    = $array[ $index ]
     $object.RRType = $array[ $index + 1 ]
     $object.Value  = $array[ $index + 2 ]

     $objects += $object

     Write-Debug $object
    }

    ## Secondary functionality:

    ## There are more efficient ways to do this, but this is easy.

    ## search for duplicate names

    Write-Host "Duplicates for $env:UserDnsDomain :"
    $hash = @{}
    $duplicates = 0
    foreach( $o in $objects )
    {
     if( $o.RRtype -eq "A" )
     {
      $name = $o.Name
      if( $skipRoot -and ( $name -eq "@" ) )
      {
       continue
      }
      if( $hash.ContainsKey( $name ) )
      {
       "Duplicate name: $name, IP: $($o.Value), original IP: $($hash[ $name ])"
                $duplicates++
      }
      else
      {
       $hash[ $name ] = $o.Value
      }
     }
    }
    $hash = $null

    ## search for duplicate IP addresses

    $hash = @{}
    foreach( $o in $objects )
    {
     if( $o.RRtype -eq "A" )
     {
      if( $skipRoot -and ( $o.Name -eq "@" ) )
      {
       continue
      }

      $ip = $o.Value
      if( $hash.ContainsKey( $ip ) )
      {
       "Duplicate IP: $ip, name: $($o.Name), original name: $($hash[ $ip ])"
                $duplicates++
      }
      else
      {
       $hash[ $ip ] = $o.Name
      }
     }
    }
    $hash = $null

    #$global:DNSobjects = $objects
    
    If ($duplicates -eq "0") {
        Write-Host "No duplicates found."
    }
    " "
    "Done"
}