dhcp deletes ddns entry

Craig craig5 at pobox.com
Tue Jun 19 22:41:13 UTC 2007

I know this was a while ago... but I just upgraded it and everything 
seems to be working better. (The clients require a release and renew, 
but DDNS seems to pick things up.) I'll need to let things settle for a 
few days to make sure, but so far so good.

And thanx for the info on the update algorithm.


Simon Hobson wrote:
> Craig wrote:
>> We have one machine (Linux: CentOS 4.4; dhclient v3.0.1) that has it's
>> ip address dynamically allocated by dhcpd (v3.0.1). But, the DHCPREQUEST
>> will trigger the DNS entry (via DDNS) to be deleted.
>> At 8:41, the client (CENTOS_CLIENT) appears to do a DHCPREQUEST, at
>> which time the dhcpd server seems to verify that the RR does exists and
>> then deletes it. (Shouldn't it do an update?)
>> Then the next time the client does a DHCPREQUEST (9:45), the RR does not
>> exists and is, obviously, added.
>> But, in the interim, the client name does not exists in DNS.
>> I am running a slightly older version of dhcpd (3.0.1), but I can't find
>> anything in the release notes that say this is fixed in 3.0.5. Also,
>> some simple web searches did not find anything.
> 3.0.1 isn't "slightly older", it's ancient ! Upgrade and see if the 
> problem is still there.
> As to "Shouldn't it do an update?", well no it doesn't work that way. 
> The algorithm is something like :
> If update required (ie lease database says it hasn't been done)
> then
>    if client hasn't said it will do forward updates
>    then
>      do forward update
>    do reverse update
> The forward update is done by
> if (both A record and matching TXT record exist) then delete A 
> record, delete TXT record, create new A record, delete new TXT record.
> The reverse update is done by
> delete PTR record(s), create PTR record.
> It's just simpler to delete any existing record(s) and create new 
> ones rather than work through all the permutations of possible 
> updates.

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