DDNS handling of "dumb" DHCP clients

Shawn Routhier sar at isc.org
Thu Aug 9 17:11:53 UTC 2012

On Aug 9, 2012, at 9:28 AM, Uwe Meyer-Gruhl wrote:

>> Right, but you can have the DHCP server assign a static address - so from the
>> device's POV it's just a regular DHCP lease (while not really a lease for
>> dhcpd).  When using the DNS name in the corresponding host declaration all you
>> need is change the DNS record, restart dhcpd and on next request the deivce
>> will get the new IP.  Nothing the client needs to know.
> You noticed the word "static" there? The whole point of DHCP is to assign dynamic addresses. With your approach, I do not even need DDNS at all, as the devices DNS entries were static as well.
> As I already wrote, we can and do use "fixed-address" now - but these addresses are derived from a database and have to be maintained for printers that are in a shared network in which pools have to be altered because of NOC contraints. I am not talking about three or four of these types here. Such modifications are done almost daily here.
> For clarity, what I want, is:
> Clients which are given dynamic addresses from a pool and for which the DHCP server does the DDNS updates WITHOUT the need for the clients to send the FQDN option (because they are "dumb").
> The DHCP server can be provided a "host" configuration entry which specifies the client's DNS name (no matter if "ddns-hostname", "hostname" or by using "use-host-decl-names" is being used), however using "fixed-address" is not an option, for the named reasons.
> And exactly that is what the documentation says ISC DHCP can do - alas, specifically only for deprecated "ad-hoc" DDNS style.

I'm not sure why it's not working for you.  It seems to be working correctly when I test it.

What version of DHCP are you using?

Do you include zone information for the DNS zones in your DHCP configuration file?

Do you include something in the host decl to identify the hosts (client id or mac address)?
Your example doesn't include them but you may have left them off to avoid clutter.

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