Simon Hobson dhcp1 at thehobsons.co.uk
Thu Oct 29 17:06:51 UTC 2009

Glen R. J. Neff wrote:

>>>ISC-bind can quite easily be configured to allow DDNS updates to 
>>>"slave" servers for a zone.  You use the 
>>>allow-update-forwarding{}; option in the zone declaration on the 
>>>slave and specify the slave server IPs in with the allow-update{}; 
>>>statement in the zone declaration on the master.
>>While the master is down ?
>Okay, I just did a basic test see what you mean.  I wrongly assumed 
>the slave would cache the updates and forward 'em on at a later time.

That is actually, in database terms, quite a hard thing to do 
reliably. It's easy to store up updates, but then you've got the 
problem of how to merge them in an orderly fashion. What happens if 
two slaves store updates - the end result depends on which notices 
first that the master is up and sends it's queued updates.

Update forwarding avoids that by the simple process of forwarding 
updates in real time, so there should be very little difference from 
sending all updates directly to the master. Unless you do a lot of 
closely spaced updates, there is no problem.


I take it you were relying on the store and forward facility then.
Simon Hobson

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