[AusNOG] PTR Records

[Mark ZZZ Smith]

----- Original Message -----
> From: Aaron Wigley <aaron.wigley at rea-group.com>
> To: David Beveridge <dave at bevhost.com>; "ausnog at lists.ausnog.net" <ausnog at lists.ausnog.net>
> Cc: 
> Sent: Tuesday, 18 November 2014, 13:16
> Subject: Re: [AusNOG] PTR Records
> 
> 
> 
> David Beveridge <dave at bevhost.com> asked:
>>  Can anyone point me to any RFC which says that there are restrictions on
>> the name a PTR can point to.
> 
> RFC 1912, under "2.1 Inconsistent, Missing, or Bad Data: Make sure your
> PTR and A records match.
> For every IP address, there should be a matching PTR record in the
> in-addr.arpa domain."
> 

RFCs aren't necessarily standards (otherwise RFC3514 evil bit implementations should now be widespread)


Highlights mine:

Network Working Group                                            D. Barr
Request for Comments: 1912             The Pennsylvania State University
Obsoletes: 1537                                            February 1996
Category: *** Informational ***





Network Working Group                                         S. Bradner
Request for Comments: 2026                            Harvard University
BCP: 9                                                      October 1996
Obsoletes: 1602
Category: Best Current Practice


The Internet Standards Process -- Revision 3

...

4.2.2  Informational

An "Informational" specification is published for the general
information of the Internet community, and *does not represent an
Internet community consensus or recommendation*.



> 
> So, if there is an A RR for mail.mycompany.com, there should be a PTR RR
> pointing back to it.  This is commonly used for email spam detection
> (https://en.wikipedia.org/wiki/Anti-spam_techniques#PTR.2Freverse_DNS_check
> s)
> 
>>  I have been told by a certain ISP that I cannot have a PTR pointing to
>> mycompany.com.au <http://mycompany.com.au> as it is NON-standard and
>> which cannot and should not be done.  They insist on setting the PTR to
>> mail.mycompany.com.au <http://mail.mycompany.com.au> and refuse to do 
> as
>> I ask.
> 
> As others have noted, that ISP is likely trying to keep their allocated
> blocks of IP addresses out of email blacklists by ensuring that PTR
> records are correct for any MX servers hosted on their IP addresses.
> 
> Regards,
> 
> -- 
> Aaron Wigley
> 
> 
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