How dhcpd chooses which server to send DDNS updates

Glenn Satchell Glenn.Satchell at
Fri May 18 12:50:58 UTC 2007

>To: dhcp-users at
>Subject: How dhcpd chooses which server to send DDNS updates
>Date: Thu, 17 May 2007 13:41:29 CDT
>From: John Hascall <john at>
>I'm wondering about the following comment in
>minires/res_findzonecut.c :
> *      ultimately we want some server addresses, which are ideally the ones
> *      pertaining to the SOA.MNAME, but only if there is a matching NS RR.
>                                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>which describes the behaviour of the res_findzonecut() function, and,
>frankly, that just seems wrong to me.  It also does not seem to be the
>behavior of, say, the nsupdate program from ISC's bind distribution.
>This makes it so a stock dhcpd, (I've modified ours), can not update
>a "hidden primary master", such as:
>     IN SOA (
>                                2007051509 ; serial
>                                36000      ; refresh (10 hours)
>                                3600       ; retry (1 hour)
>                                604800     ; expire (1 week)
>                                360000     ; minimum (4 days 4 hours)
>                                )
>                        NS
>                        NS
>where xx-0 is the master and dns-1/dns-2 are the externally visible
>slave servers.
>Is there any chance this is might change in future versions or am I
>going to be stuck making this mod from now on?
>PS, it's about a 25 line change if anybody else is interested

How about a 3 line change to dhcpd.conf to define the name server for
the zone? This is based on the entry in the dhcpd.conf man page under

     zone {
     The primary statement specifies the IP address of  the  name
     server whose zone information is to be updated.


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