Re: Is it possible to query DNS for a SRV record in perl?

[Christopher A B. <ca...@tc...>]

As K Reddy once put it so eloquently:

> Instead, he suggested that I query DNS for the SRV
> record, which looks like this: 
> _.gc._tcp.us-city._sites.company.com. 
> 
> It worked when I used nslookup from a DOS prompt, but
> I'm not sure how to look it up in UNIX. 
> I tried the Net::DNS module, but I honestly couldn't
> figure out how (or if) it works for looking up SRV
> records. 

Here is the code we use to lookup the PDC for doing Active Directory
updates, using Net::DNS.  Call it with the domain that you're trying
to update.  Returns a hostname and port.  Note that I "hardcode" in
the LDAPS port (via getservbyname) since MS doesn't define _ldaps as a 
service name.  Change ldaps to ldap in the getservbyname, or return
$rr->port to use the port in the SRV record, if you want non-ssl LDAP.

####snip
sub lookup_pdc {
  my ($dc) = @_;
  my $res = new Net::DNS::Resolver;
  my $query = $res->send("_ldap._tcp.pdc._msdcs.$dc", "SRV");
  if ($query) {
    foreach $rr ($query->answer) {
      next unless $rr->type eq 'SRV';
      # return first found; find ldaps port from services file since
      # there's no _ldaps SRV record
      return $rr->target, scalar getservbyname('ldaps', 'tcp');
    }
  } else {
    &note("SRV lookup failed: " . $res->errorstring);
  }
  return;
}
####snip

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