dhcpd.conf for dynamic dns

Simon Hobson dhcp1 at thehobsons.co.uk
Tue Mar 20 09:41:36 UTC 2007

Chow Chi Ho \(FP&HO\) wrote:

>>This server will NOT overwrite an existing record that it did not put
>>there itself - this is to stop someone naming their machine the same
>>as one of your servers and hijacking connections to it !
>>Delete the record and try again, the dhcp server will attempt to
>>update again next time the client renews. If that is successful then
>>you will see the A record and an additional TXT record which is a key
>>put there so that the DHCP server knows that it created the record
>>and so it can safely delete or replace it.

>any way to force the updating even the records are exist  on dns ?

No there isn't. I'm afraid you'll just have to go through your DNS 
zones and weed out all your dynamic client records. It's a one-off 
task so shouldn't be too much of an issue.

If you are concerned about not having client dns records for a while, 
then one way to mitigate this is to reduce your lease times in 
advance. Eg, if you currently use 7 day leases, then you would have a 
window of about 3 1/2 days during which the client dns records will 
get re-added. If you reduce the lease time to 1 day then you reduce 
this window to about 12 hours - but you need to do this a week before 
you weed the dns to guarantee that all clients are working to the 
shorter leases. The day before, you could reduce the lease times to a 
few hours - but don't go too short as you don't want too many clients 
all renewing and causing DNS updates too fast. Once all the clients 
have renewed at least once, you can increase your lease times again.

PS - Please learn how to trim unneccessary quoted material and put 
your reply below the quoted text to which it refers - I know it's not 
the easiest thing to do with stupid Microsoft mail programs. It makes 
things a lot easier to follow and was accepted email etiquette before 
Outlook came along with it's silly defaults.

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