Multiple PTR-records

[Kevin Darcy]

Christopher Rasch-Olsen Raa wrote:

>Hi,
>
>Is it incorrect to specify more than one PTR record for the same IP. eg:
>I have one IP which hosts more than one site. www.something1.com,
>www.something2.com, www.something3.com and www.something4.com all points
>to 123.123.123.123, and I wonder if I should provide PTR-records for all
>of those names. Should I?
>
It's legal, but there is no point in doing so, since all known client 
applications only look at the first PTR record in the response, and most 
if not all software that uses reverse lookups for "authentication" only 
cares whether the name obtained via the reverse lookup resolves to the 
same address with which it started, which will be true whether the 
reverse-lookup response contains 1 PTR record or 50 of them. Also, if 
you take multiple-PTR-responses to ridiculous extremes -- as some sites 
have done -- you end up with huge DNS responses that need to be retried 
using TCP, and this causes all sorts of problems.

                                                                         
                                                - Kevin