question regarding recommended PTR record configuration with multiple mail sites hosted on same IP

[Kevin Darcy]

Gregory Hicks wrote:

>>Date: Thu, 09 Feb 2006 02:17:04 -0600
>>From: Albert Croft <acroft at cyber-wizard.com>
>>To: BIND Users Mailing List <bind-users at isc.org>
>>Subject: question regarding recommended PTR record configuration with multiple 
>>    
>>
>mail sites hosted on same IP
>  
>
>>I appologise if I waste anyone's time-I just wish to be clear on something.
>>
>>I often see mentioned that there should be a PTR record set up for a 
>>mail server, but what is the recommendation in a case where multiple 
>>sites share a mail server? In other words, there exists something like 
>>(I can provide actual hostnames/IPs, if needed):
>>
>>host.domain00.com. IN A 1.2.3.4
>>mail.domain01.com. IN A 1.2.3.4
>>mail.domain02.com. IN A 1.2.3.4
>>mail.domain03.com. IN A 1.2.3.4
>>
>>Should there be a PTR record for each name entry? Or just one, and if 
>>so, what should it refer to? I seem to recall seeing mention in an older 
>>copy of _DNS_and_Bind_ of some systems not behaving properly when seeing 
>>multiple PTR records-is this still the norm?
>>    
>>
>
>Pick one name as the 'owner' of the PTR and make a PTR record for that
>name.
>
>The problem with multiple names for PTRs is the way that Bind handles
>multiple names assigned to one IP address.  It make a "round robin" out
>of them.  
>
You call that a "problem"; I call it a feature. If folks are stupid 
enough to create multi-record PTRs, then they deserve some 
unpredictability in their reverse lookups. In the not too distant past, 
BIND had a special case for PTRs (or perhaps it was everything but 
A/A6/AAAA records), so that they wouldn't be "round-robin"ed. Apparently 
that has now changed. Sometimes you have to be cruel to be kind. These 
folks will learn their lessons and change their evil ways.

>I get a reply containing all four records.  You would get a
>reply containing all four records but the first record that *I* got
>becomes the last record that you get.  Your first record bcomes the
>last record that someone else gets...  And so on.
>  
>
Actually, I think BIND still doesn't implement true "round-robin", where 
it keeps state about the last answer given. The default rrset-order is 
"cyclic", with the starting record of the set being picked randomly.

- Kevin