A record of domain name must be name server ?

Mark Elkins mje at posix.co.za
Thu Sep 11 15:51:52 UTC 2014


On Thu, 2014-09-11 at 11:27 -0400, Kevin Darcy wrote:
> Mark,
>             Depending on implementation, a PTR RRset with multiple
> records either
> 
> -- only ever gets answered with the "first" record of the set (in
> which case the second and subsequent records of the set are just a
> waste of space), or
> -- answers in a random, cyclic and/or round-robin fashion (in which
> case, the results are non-deterministic from the standpoint of a
> client, and this can cause problems and/or confusion)


Last time I checked, ALL matching records are returned as a single
Resource Record Set - (and in the case of DNSSEC - covered with a single
signature).

What the receiver does with it is up to that receiver... as you say -
some of the information may be discarded.

> So, although the standards allow multiple RRs, in practical terms, it
> only makes sense for a PTR RRset to contain a *single* RR.

I would still disagree. When there is forward<-->reverse checking, one
may need the complete answer. I certainly have some processes that do an
exhaustive check.


- Kevin
> 
> On 9/11/2014 3:45 AM, Mark Elkins wrote:
> 
> > On Wed, 2014-09-10 at 18:13 -0400, Kevin Darcy wrote:
> > > No, what I'm saying is that if
> > > 
> > > example.com owns an A record 203.0.113.48, and
> > > www.example.com owns an A record 203.0.113.48, then
> > > 
> > > where does 48.113.0.203.in-addr.arpa point?
> > > 
> > > Some people will point it at example.com, some will point it at 
> > > www.example.com. What you get is a mish-mosh. No consistency.
> > Although I prefer the use of a CNAME solution (CNAME www.example.com to
> > example.com), in the case of separate A (and AAAA) records, one could
> > point the reverse to both names. Nothing wrong with a PTR record having
> > more than one answer. There is then no inconsistency, just choice. After
> > all, pretty much every NS record has at least two Right-Hand-Sides
> > (Answers)....
> > 
> > 
> > > If, on the other hand, www.example.com is a CNAME to example.com, then 
> > > it's crystal clear where the reverse record will point -- example.com. 
> > > There is no ambiguity or option for inconsistency.
> > > 
> > >      - Kevin
> > > 
> > > On 9/10/2014 5:48 PM, Eliezer Croitoru wrote:
> > > > Hey Kevin,
> > > > 
> > > > This is not an issue at all.
> > > > A PTR is different then a "A" record and can be used by two reverse 
> > > > domain names and only the owner of the IP addresses space can define 
> > > > them.
> > > > I am not sure if two PTR records for two domains will be applied to 
> > > > one IP but it is possible for two IP addresses to have the same PTR.
> > > > 
> > > > Can we even use a CNAME as a PTR???
> > > > 
> > > > Eliezer
> > > > 
> > > > On 09/11/2014 12:37 AM, Kevin Darcy wrote:
> > > > > Also, have you considered the forward/reverse ambiguity that arises when
> > > > > multiple owner names resolve to the same address? To which of those
> > > > > names does the PTR point?
> > > > > 
> > > > >      - Kevin
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-- 
Mark James ELKINS  -  Posix Systems - (South) Africa
mje at posix.co.za       Tel: +27.128070590  Cell: +27.826010496
For fast, reliable, low cost Internet in ZA: https://ftth.posix.co.za
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