Multiple PTR records

[Peter Apockotos]

Well I never assumed to use multiple PTR records one IP, I am new to BIND
not DNS.  But I did not know if he had a trick up his sleve.

on 06/07/2001 04:43 AM, Marc Thach Xuan Ky at Marc.Thach at reuters.com wrote:

> On 06/06/2001 20:47:10 bind-users-bounce wrote:
>> Yes. But you may have to make a choice about where to point the reverse
> records.
>> 
>> 
>> - Kevin
>> 
>> Peter Apockotos wrote:
>> 
>>> So then it is ok to give the same IP addresses that the testdomain.com has
>>> to the testdomain.net ?
>>> 
>> 
> 
> Kevin implies here that only one PTR record should be defined for one IP
> address
> (in the presence of the number of A records using that address), whereas the
> other day, he and Brad were having a laugh and incidentally referring to
> mul;tiple PTRs as below:
> 
>>> Multiple
>>> A records can point to the same address, true, but my (facetious)
> assumption
>>> was that every A record had a corresponding PTR record:
>> 
>> Do you mean that multiple names could point to the same A record?
>> If so, yes that is certainly true.
> 
> After reading too many RFCs I decided to have a policy to apply by default PTR
> records for each A record in my database.  So when I saw these mails I had a
> look through the archives and found a thread where Cricket (Feb 99) had said:
> 
>> However, a resolver that retrieves all those PTR records may not do
>> anything intelligent with them.  At best, it'll probably just take the
>> first one in the list and ignore the rest.
> 
> Barry Margolin notes:
> 
>> While this is true, I generally recommend *against* multiple PTR records if
>> you don't have a good reason for them.  They're rarely all needed, and they
>> don't really service much purpose.  Because of round-robin, they'll result
>> in non-deterministic output from programs that translate addresses to
>> names.  And if you're using hostnames in access files (e.g. .rhosts) you'll
>> need to list all the names.
>> 
>> It's important that every PTR record have a corresponding A record, but
>> it's not usually necessary for every A record to have a corresponding PTR
>> record.
> 
> Cricket:
> 
>> PTR records aren't round robinned, though--at least in BIND.  Here's
>> the salient section of ns_resp.c:
>> 
>> ................
> 
> Then there was a similar thread in Dec 99, and a few references in Oct 99.
> The
> consensus seems to be that it's best not to add multiple PTR records.  All
> well
> and good but how do I select which domain name to use in the single PTR
> record?
> Nobody seemed to touch on this.  It needs to be a pragmatic decision, but in
> the
> absense of mail servers, where I'm not expecting anybody to be using
> r-utilities, what other criteria should I be looking at?
> Rgds to all,
> Marc TXK