Reverse address entries

Sam Wilson Sam.Wilson at
Fri Jul 12 15:22:41 UTC 2013

In article <mailman.736.1372773195.20661.bind-users at>,
 Steven Carr <sjcarr at> wrote:

> 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.

"... can also be configured ..." - see below.

> > 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.

Sorry for the delay in returning to this.  RFC 1912 says:

Status of this Memo

   This memo provides information for the Internet community.  This memo
   does not specify an Internet standard of any kind. ...

To make myself clear, I'm a big fan of correct PTR records and we try to 
make sure that our reverse DNS is fully populated.  I do not regard lack 
of a valid PTR record to be a reason to refuse connection except, 
perhaps, in very particular circumstances, for instance where it might 
be part of a trust stance.  That would be by agreement between 
consenting adults, not the law of Internetland in general.


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