Reverse address entries

Steven Carr sjcarr at
Tue Jul 2 13:52:44 UTC 2013

On 2 July 2013 14:42, Sam Wilson <Sam.Wilson at> wrote:
> Can anyone here give examples of the types of various software that will
> not operate without a PTR record?

There have already been numerous listings of software that require
reverse lookups. SMTP being the main one. Other services like IRC and
some databases (Oracle/MySQL) can also be configured to require
properly working reverse lookups.

> 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.

RFC1912 [] section 2.1...

Every Internet-reachable host should have a name... Make sure your PTR
and A records match.  For every IP address, there should be a matching
PTR record in the domain.  If a host is multi-homed,
(more than one IP address) make sure that all IP addresses have a
corresponding PTR record (not just the first one). Failure to have
matching PTR and A records can cause loss of Internet services similar
to not being registered in the DNS at all.  Also, PTR records must
point back to a valid A record, not a alias defined by a CNAME.


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