All PTR (reverse DNS) names are in lower-case



For example, when I DIG PTR of some IP address using Google DNS or Quad9, it will show:

[[email protected] ~]$ dig +short ptr -x @
[[email protected] ~]$ dig +short ptr -x @

The same situation is on my ISP’s DNS server (which is not accessible over IPv6 Internet - the main reason why it is secondary for me):

[[email protected] ~]$ dig +short ptr -x @195.42.x.y

And, now I’ve performed DIG PTR using Cloudflare DNS:

[[email protected] ~]$ dig +short ptr -x @

And have seen that all letters of the result are in lower-case.
Is this a bug or Cloudflare’s principled policy of reverse DNS namings?


Host names are not case sensitive


I don’t know about these essentials, but this may cause some ambiguities, only look at this:

[[email protected] ~]$ dig +short ptr -x 93.x.y.z **@**
[[email protected] ~]$ dig +short ptr -x 93.x.y.z **@**

At the first dig the construction “wsx…10ge” turns into some abracadabra, but at the second - 10GE denotes 10GigE interface.

I’m ONLY asking ABOUT THIS. Are there any ways to get the same result as from DNS? Of course, leaving Cloudflare’s DNS :slight_smile:


Well, Cloudflare seems to lowercase hostnames in these cases. I am not sure but I doubt there is something you could do from your side to avoid this and Cloudflare is perfectly within the specifications as hostnames are not case sensitive.


Well. It is no matter. Only a small Cloudflare DNS difference. However, maybe it is a fault of these ISPs - making case sensitive hostnames. I don’t have any contacts with them. Only tracing routes to check backbones connectivity and noticed this difference. But in general - Cloudflare DNS is the very good project. The latency with my home router and only 6 ms. I will use it for a some time. OK. Good bye.


I wouldnt call it their “fault” either. Host names are traditionally lower case, but as they are case insensitive there is nothing that prevents one from using upper case characters either.

In Cloudflare’s case it simply seems they convert them to lower case by default for some reason.