dhcp and dynamic dns updates

[David W. Hankins]

On Wed, Mar 04, 2009 at 09:22:16AM +0100, Tom Schmitt wrote:
> Wouldn't it help, if you simply install a caching-only Bind on the DHCP-server who is only listening to 127.0.0.1? At least for the updates the dhcpd would get his answer instantly and the time consuming work is done by the local Bind asynchronously. For normal lookups it would of course only help if the answer is in the cache already. 
> Looks like an easy workaround to me.

No...updates don't work that way.  Even if you have a server that
forwards updates, it does not reply until it receives the reply from
the upstream server.

Updates carry pre-requisites, then add/delete commands based upon
them.  The standards-based DHCP->DDNS udpate protocols use the PREREQs
to form kind of "atomic locks" on DDNS actions.  There are two or
three steps in some cases.

So the update reply has to include the correct RCODE or else the
mechanism will be utterly broken; we couldn't know wether to proceed
to the next step, retry a previous step, or be done with it.


It does help, like I said, to have the "master" for the zone colocated
with the DHCP server, listening on 127.0.0.1, and then to have your
"real" DNS server slave the zone ("hidden master").

-- 
David W. Hankins	"If you don't do it right the first time,
Software Engineer		     you'll just have to do it again."
Internet Systems Consortium, Inc.		-- Jack T. Hankins
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