reverse dns for multiple domains on same subnet

Kevin Darcy kcd at
Tue Jan 4 23:09:03 UTC 2005

Nick Trenary wrote:

>I have two domains on my subnet, call them and on 
>  How is reverse DNS configured?  There can be only one 
> zone file, right?  If so, how is it configured for 
>multiple domains if both domains point to the same IP address?
First ask yourself why you care about reverse records in the first 
place. Is it because some silly app wants to "authenticate" a client by 
doing a reverse lookup on its source address, followed by a forward 
lookup of whatever it got from the reverse lookup -- the so-called 
"double lookup" -- to verify that it gets the IP address with which it 
started? If that's the case, then it only matters that the reverse 
lookup returns *one* of the (possibly many) names which happen to 
resolve to the relevant IP address. So just pick one forward name for 
each address and be done with it. Or use some heuristic, e.g. in case of 
multiple references, the alphabetically-highest name wins.

If you have some other reverse-DNS requirement(s) beyond "source-address 
authentication by double lookup", then you need to define those more 
clearly, to see if CNAMEs or some other technique will satisfy it/them.

- Kevin

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