Re: Multiple PTR records

[Kevin Darcy <kcd@daimlerchrysler.com>]

Mark.Andrews@nominum.com wrote:

> >
> > To clarify: there is nothing in the DNS protocol to stop you from creating mu
> > ltiple
> > PTR records with the same name, however no app is known to actually look beyo
> > nd the
> > first PTR in a response, and because of this fact BIND suppresses RR sorting
> > for
> > PTR records. So essentially all PTRs beyond the first one are "invisible" and
> >  a
> > waste of packet space (if the response overflows the 512-byte limit, then it
> > may
> > also waste TCP retransmissions too).
> >
> >
> > - Kevin
>
>         Some site even go so far adding PTR records that they exceed
>         the protocols ability to send them in a response.  I wonder
>         about sites that do this and how much else they don't know
>         about.
>
>         You could even use multiple PTR records as a filtering
>         critera when selecting web hosting providers.  If they list
>         multiple PTR records then they most probable don't know
>         what they are doing and you should shy away from them.
>
>         It sound like you are trying to learn what to do which is
>         good.  Good luck and keep up the learning.

I wonder if this would be good BCP material (?). RFC 2181 (not a BCP of course but
Standards Track) almost seems to *encourage* multiple PTRs by "clarifying" that it
is supported in the protocol. Now that the cat is out of the bag, perhaps there
should be a BCP stating that, while multiple PTRs are technically possible, they
are generally undesirable and when taken to extremes can in fact cause problems.

I would not volunteer to write such a document, of course, given my
even-more-radical view that reverse DNS should probably go away or its use be
severely limited (and I don't think keeping reverse DNS around solely as a sort of
"ISP intelligence test" is really a strong argument, even when couched in terms of
spam-prevention).


- Kevin