"update-optimization false" and ddns-fwd-name / client-hostname

[Nicolas C.]

Hello,

I'm using two dhcp servers in failover mode (v.4.2.2, Debian Wheezy), 
the primary failover hosts a bind server.

We have DDNS in place and, to make sure the dynamic zones are 
up-to-date, we have the "update-optimization false" option on both servers.

For some workstations, the DHCP keeps renewing the leases but does not 
perform the DNS update. We know this happens on some workstations always 
powered on (easy to detect) but it may also happens for regular clients 
connected during office hours.

There are two workaround to this problem :

  - on the client : force a DHCPRELEASE + DHCPDISCOVER

  - on the server : put a temporary "deny booting" to force the client 
to renew its lease on the other server (it forces the DNS update).

I made a tcpdump capture and did not find anything unusual, restarting 
the DHCP server has no effect.

After reviewing the lease file, I found that the "client-hostname" 
doesn't match the "ddns-fwd-name".

Is this the cause of the DDNS failure? If yes, is there a reason why 
ddns-fwd-name/client-hostname are not the same?

lease 172.20.11.145 {
   [...]
   uid "\001\000\014)\371_\335";
   set ddns-rev-name = "145.11.20.172.in-addr.arpa.";
   set ddns-txt = "31bf1c64c8bdb1545e31ab674317707873";
   set ddns-fwd-name = "windows-dedevh1.domain.ltd";
   client-hostname "WIN-SQ6ADOG23I8";
   }

Regards,

Nicolas