Reverse DDNS on classless zones

Simon Hobson dhcp1 at
Wed Jul 18 15:30:08 UTC 2012

Subject fixed, surplus quoted stuff trimmed, and bottom posting ...

atif yameen wrote:

>Thanks for the reply. I have gone through the rfc 2317. I do have 
>all the cnames required in the right format in my parent zone, i.e. 
>129.119/16. The issue is with DHCP not registering the record in the 
>right format. it does register it in the right zone but not the 
>right format.

It won't do, and never will.
The DHCP server will do exactly one thing - reverse the octets and 
append the zone specified. It does not understand the rfc2317 bodgery 
and is never likely to. So for a client w.x.y.z, the DHCP server will 
never set the reverse DNS for anything but z.y.x.w.<something>. 
<something> defaults to, but as you've realised this can 
be changed.

So I'd suggest forgetting about the RFC2317 format. Just set yoursefl 
up a zone like, set ddns-rev-domainname to, and set your CNAMEs to point to,, and so on.

Simon Hobson

Visit for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.

More information about the dhcp-users mailing list