Reverse address entries

[Sam Wilson]

In article <mailman.727.1372684591.20661.bind-users at lists.isc.org>,
 Matus UHLAR - fantomas <uhlar at fantomas.sk> wrote:

> >> >In article <mailman.710.1372442831.20661.bind-users at lists.isc.org>,
> >> > Charles Swiger <cswiger at mac.com> wrote:
> >> >> Certainly.  Various software performs what's called a double-reverse
> >> >> lookup
> >> >> to confirm that the A and PTR records match.
> 
> >In article <mailman.718.1372672345.20661.bind-users at lists.isc.org>,
> > Matus UHLAR - fantomas <uhlar at fantomas.sk> wrote:
> >> He apparently meant exactly the same. Also calles FcRDNS - "forward
> >> confirmed" or "full circle" reverse DNS.
> 
> On 01.07.13 14:11, Sam Wilson wrote:
> >OK.  So what Mr. Swiger refers to is not relevant - it's no reason to
> >add PTR records.
> 
> Yes, it is.
> 
> "Various software performs what's called a double-reverse lookup to confirm
> that the A and PTR records match."
> 
> It means that various software checks your PTR and then A (or maybe
> AAAA) records, and can fail if eny of them is not found ot rhe latter result
> doesn't match the original IP address.

There may be a subtle language thing going on here.  I read the original 
post above as saying, literally, "you need PTR records because various 
software tries to match A and PTR records".  It doesn't say "you need 
PTR records because some systems require PTR records (and if you have 
them they will also need to match the A records)".  PTR records are nice 
but they aren't a general requirement.

Can anyone here give examples of the types of various software that will 
not operate without a PTR record?

> Now that IS a reason to add PTR for IP address, and they must point to
> hostnames that point to the same IP.

I agree that if PTR records exist then they should match an A record.  
My experience (and IIRC correctly the word of several RFCs) is that PTRs 
are not required for most things to work.

Sam

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