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I read in easyDNS that, in order to set up reverse DNS, "The IP block must be delegated to our nameservers by your ISP." Is that always the case? What if you decide to host your name servers? Will adjusting the PTR records suffice? Some discussions on the web lead me to think that it isn't.

After these boolean questions (in particular if the answers are negative), please feel free to elaborate the DNS 101 concepts behind them. In my no-background mind, it looks like you are "given" that IP address (say, by your VPS hosting company), and that you should be able to "tell the world" that, having reached that IP, it corresponds to domain example.com.

Thanks!

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2 Answers 2

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It depends on the provider and its policies. Normally, you will not delegated reverse DNS authority without you having some large block of continuous IP space. If it's just normally one to eight IPs, you won't get control over it. In that case the ISP will handle reverse DNS.

In most hosting situations you must send in a support ticket to contact the ISP/Upstream/Datacenter/Etc to update the PTR record. But, some providers, like Softlayer, allow you modify it yourself via a control panel.

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Thanks for your answer (not enought reputation to upvote you). I'm clearly clueless about DNS architecture, but it seems to me unfair that the party that "rented" this IP address (even if it is just one IP) cannot make the IP -> domain mapping without interference. I will read enough about it to understand it... some day! –  eze Nov 6 '10 at 23:01
    
RDNS should be something you set once and not touch for a long time, if you want to change your PTR often, without human verification, most hosts would probably think you were a spammer. –  Justin Bieber Nov 6 '10 at 23:51
    
@user59240 it's not "unfair", it's just that reverse DNS was designed before classless subnetting (CIDR) and so the zone boundaries are to the nearest /8, /16 or /24. –  Alnitak Jan 10 '12 at 9:49

Reverse DNS, just like forward DNS, is divided with dots. Reverse DNS gets formatted somewhat oddly -- 1.0.0.127.in-addr.arpa. -- which presents issues for breaking up a subnet on anything other then historical classful boundries (ie, splitting on a dot.) If you have anything smaller than a /24, you'll typically only be able to change reverse DNS via a control panel or ticket to your provider.

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