is reverse dns required? (policy question)

Fri Dec 3 10:02:13 UTC 2004

Mark Andrews wrote:
> In article <41AF5C33.4050202 at nrg4u.com> you write:
> 
>>You would put in a global wildcard that says no smtp sender here.  Only
>>for those boxes being legitimate SMTP to outside senders you'd put in a
>>more specific record as shown above.  You probably have to enter some dozen
>>to one hundred servers this way.  Sure your reverse zone scripts need some
>>changes but it's only two or three lines.
>>
>>Ideally you could tell your DNS server in the zone file this:
>>
>> _send._smtp._srv.*.*.173.128.in-addr.arpa.   IN TXT   "0"
>> _send._smtp._srv.*.*.82.198.in-addr.arpa.   IN TXT   "0"
>>
>>being overidden by more specific information on single IP addresses.
> 
> 
> 	You obviouly do not know how wildcard work in the DNS or you
> 	would not have made this suggestion.  Please read RFC 1034
> 	and work though Section 4.3.2. Algorithm with a QNAME of
> 	_send._smtp._srv.1.1.173.128.in-addr.arpa.

The wildcards are in the DNS server zone file for interpretation by the
DNS server itself.  It would not be published as such because that obviously
wouldn't work as you prove.  But nothing is preventing BIND or whatever
from taking this wildcard record and answering every request with the
wildcard "_send._smtp._srv.*" RR if no more-specific exists.  This should
be relatively straight forward to code.  Wouldn't want to touch the code
base of BIND but for DJBDNS I could somewhat easily implement it.

-- 
Andre