[ On Wednesday, December 31, 2003 at 16:23:58 (+0100), Kjetil Torgrim Homme wrote: ]
> Subject: Re: [Exim] Inbound Hosts without valid rDNS
>
> note it says "for every IP address", not "for every A record".
If you had bothered to try and understand the reverse DNS and how the
DNS as a whole is designed then it would be abundantly clear to you
that what you've quoted is incomplete, and what you say above is
extremely misleading.
> [RFC 1034]:
> | A type PTR query is used to get the RR with the primary name of
> | the host. For example, a request for the host name corresponding
> | to IP address 1.2.3.4 looks for PTR RRs for domain name
> | "4.3.2.1.IN-ADDR.ARPA".
>
> note "primary name of the host", indicating that there is only one.
Note also the use of a plural word in the phrase "looks for PTR RRs".
The use of the word "primary" in the phrase you quote is only an
accidental historical artifact of how the authors thought at the time
that RFC was written oh so many years ago. Trust me -- I was around
back then and I paid very close attention to all these issues even back
then.
Furthermore if you want an even more authoritative "standards track"
statement about the validity of multiple PTRs you should read RFC 2181,
and in particular section 10.2:
10.2. PTR records
Confusion about canonical names has lead to a belief that a PTR
record should have exactly one RR in its RRSet. This is incorrect,
the relevant section of RFC1034 (section 3.6.2) indicates that the
value of a PTR record should be a canonical name. That is, it should
not be an alias. There is no implication in that section that only
one PTR record is permitted for a name. No such restriction should
be inferred.
> so traditionally, you will find only one PTR RR,
Traditionally you'll only find one PTR RR for any given address because
the traditional API most often used for retrieving a hostname given its
address was based on that ancient and venerable HOSTS.TXT file where
there was only one hostname for every address and vice versa.
Then when the DNS came along the folks at Berkeley decided they could
extend the API for their new gethostbyaddr() call to work with the DNS
and they similarly extended their own /etc/hosts file to allow for
multiple hostnames in a single entry.
Unfortunately even today application programmers continue to put some
sort of credence in the ancient structure field names and header file
comments.
There is _no_such_thing_ as an "official" or "primary" hostname in the
DNS, nor can there ever be any such construct, _by_its_very_design_.
> trying to get that
> changed will be almost impossible.
You wouldn't know unless you've tried it as I have many times, in which
case you'd have found out that it's not that difficult at all in the
vast majority of cases and then you wouldn't have said what you said.
--
Greg A. Woods
+1 416 218-0098 VE3TCP RoboHack <woods@???>
Planix, Inc. <woods@???> Secrets of the Weird <woods@???>
