Here is the code I use for IP to HostName:

use Socket; # For Binary-> IP dot quad etc...
use Net::Whois::IANA; # For IP -> Name

# Get IP addr
# Call the sub below, and print value

sub Get_Whois_Name {
  my $ip = shift;
  my $Save_ = $_; # The WhoIs module messes with $_ (BUG!!)
    # Save current value for restore upon exit.
  ##print "LOOKING FOR $ip ====";
  my $iana = new Net::Whois::IANA;
  $iana->whois_query(-ip=>$ip);
  my $name = $iana->descr();
  if ($name =~m/not allocated/){
     $name = "Country=" .$iana->country() ."+Net=" . $iana->netname();
  }
  #Zap commas in name
  $name =~s/\,/ /g;

  $_ = $Save_; # Restore
  return $name;
}
##########################################
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