Finding all CNAMEs associated with an A record

[Kevin Darcy]

Anshuman Kanwar wrote:

>Hi all,
>
>Given that I created a many to one relation between CNAMEs records and an A
>record, is there a way to get a list of all CNAMEs by querying the A name ?
>
>example :
>
>bird     IN  A      192.168.0.5
>chicken  IN  CNAME  bird  
>hen      IN  CNAME  bird  
>rooster  IN  CNAME  bird  
>
>Now I want run some commad, which gives me :
>
># some-command bird
>chicken
>hen
>rooster
>
As long as you're limiting yourself to CNAMEs that are in a particular 
zone, then this should be a fairly easy Perl script to write. Basic 
structure: do a zone transfer of the specified zone, looking for CNAME 
records with the specified name in their RDATA. Quick-and-dirty:

#!/usr/bin/perl

use Net::DNS;

($target, $zone) = @ARGV;

$res = new Net::DNS::Resolver;
foreach $rr ($res->axfr($zone)) {
    print $rr->name."\n" if (($rr->type eq "CNAME") && ($rr->rdatastr eq 
$target."."));
}

But, of course, CNAMEs in one zone can point to a name in a completely 
different zone. Without downloading every zone in existence, there's no 
way to know for sure whether one of them might contain a CNAME reference 
to any given name.

                                                                         
                                          - Kevin