Listing 1. Querying for All DCs in a Domain

use strict;
use Net::DNS;

Begin comment
# Specify the domain name on the command line
# or use the default.
End comment
my $domain = $ARGV[0] || 'amer.xyz.com';

print "Querying for Domain Controllers in $domain\n";

# Begin callout A
my $res = Net::DNS::Resolver->new();
# End callout A
# Using nameservers() is optional.
# Begin callout B
# $res->nameservers(‘17.70.16.18’);
# End callout B
# Begin callout C
my $query = $res->search("_ldap._tcp.dc._msdcs.$domain",
  "SRV");
# End callout C

if ($query) {
# Begin callout D
   foreach my $rr ($query->answer) {
# End callout D
      next unless $rr->type eq "SRV";
      print $rr->target,"\n";
   }
}
else {
   die "DNS query failed: ", $res->errorstring, "\n";
}