#!/usr/bin/perl -w

# checkDNS.pl - A forward & reverse DNS query script
#
# 25 May 2005
# Christopher Juckins
#
# Script checks hosts in a particular IP address range for DNS entries.
# It's a quick and dirty way to see what IP addresses are associated
# with DNS entries on your network.
#
# Script asks user for the following input:
# Network (Example: 205.165.5)
# Begin host to check (Example: 1)
# End host to check (Example: 254)
# DNS Server to use for lookups (Example: 205.165.5.242)
#
# Script runs, doing a 'host' lookup on each address in the range.
# If a host is found, it is then checked for forward (normal) DNS.
#
# If nothing is returned for a particular entry, it is noted and
# the forward lookup will not run for that entry.
# Duplicate entries are also returned for the reverse checks.
#
# The output prints to screen and also to /tmp/checkDNS.txt

print "Enter network in form XXX.XXX.XXX <Ex. 205.165.5> -->";
$NETWORK = <STDIN>;
chomp($NETWORK);

print "Enter start range of IP to scan <Ex. 1> -->";
$BEGIN= <STDIN>;
chomp($BEGIN);

print "Enter end range of IP to scan <Ex. 254> -->";
$END = <STDIN>;
chomp($END);

print "Enter DNS server IP address to use for checking <Ex. 205.165.5.242> -->";
$SERVER = <STDIN>;
chomp($SERVER);

# Open file for output
open (OUTPUT, ">/tmp/checkDNS.txt");

print "\nReverse DNS lookup follows...\n";

for ($ip = $BEGIN; $ip <= $END; $ip++) {
   # Create host to check
   $host = "$NETWORK." . "$ip";
   # Create query for 'host' command
   $query = "$host" . " $SERVER";
   # Store info that is returned from the query
   $dns = `host $query`;
   # Split apart the multiple lines that get returned
   @dns = split(/\n/, $dns);
   # Only get the lines that have data we want (domain name pointer)
   foreach $entry(@dns) {
      if ($entry =~ /domain\sname\spointer/) {
         @entry = split(/\s/, $entry);
         # Get index value for the last array element
         $last = $#entry;
         # Remove annoying trailing period (.)
         if ($entry[$last] =~ s/\.$//) {
         }
         print OUTPUT "$host, "."$entry[$last]\n";
         print "$host, "."$entry[$last]\n";
         # Set up array for forward zone checking
         push(@forward,$entry[$last]);
      }
      if ($entry =~ /not\sfound/) {
         print OUTPUT "$host, NOT_IN_USE\n";
         print "$host, NOT_IN_USE\n";
      }
   }
}

# Now do forward lookup
print "\nForward DNS lookup follows...\n";
foreach $entry(@forward) {
   $dns = `host $entry`;
   # Clean up printed output
   if ($dns =~ s/\shas\saddress/,/) {
   }
   print OUTPUT "$dns";
   print "$dns";
}