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