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December 20, 2006

A Few Comments on Poorly Chosen Reverse DNS / PTR Naming

Over the past three years and then some, I've done a lot of reverse DNS lookups. What I've found has been insanely boring even on the best days, but occasionally there's a stroke of brilliance, or naming of such stupefying uselessness that it amazes even jaded old me.

Let's look at the purpose of a PTR record, according to the RFCs that defined it. 

3.3.12. PTR RDATA format


    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

    /                   PTRDNAME                    /

    +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+



where:



PTRDNAME        A <domain-name> which points to some location in the

                domain name space.



PTR records cause no additional section processing.  These RRs are used

in special domains to point to some other location in the domain space.

These records are simple data, and don't imply any special processing

similar to that performed by CNAME, which identifies aliases.  See the

description of the IN-ADDR.ARPA domain for an example.

Now granted, that's a pretty sparse definition: a PTR is a domain name which points to some location in the domain name space. In practice, PTRs are the result when you're trying to find more information about an IP address you already know.

So, then, why, god, why, do so many people insist on including 'ptr', 'rev', 'reverse', 'ip', and so forth in their PTR records? Isn't that redundant?

Posted by schampeo at December 20, 2006 1:49 PM

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