different ip address between clients restarts

[Radoslav Pešek]

Hallo list, I have dhcp servers (Debian 8.5, version 4.3.1, failover 
mode, ddns-update-style interim) and (at least) for certain clients they 
don't keep ip address between clients' restarts.

Its maybe related to another issue I posted few days ago - 
https://lists.isc.org/pipermail/dhcp-users/2017-June/020652.html - but 
the solution only helped for problem with weird hostname value in dhcp 
replies, not for this issue as I hoped.

So, it's in failover mode (interim) with clients getting ip addresses 
from range. The pool shouldn't be exhausted as I see this in logs:

Jun 27 10:08:39 s3 dhcpd: balancing pool b8107778 poschodia_a_studenti  
total 21  free 4  backup 5  lts 0  max-own (+/-)1
Jun 27 10:08:39 s3 dhcpd: balanced pool b8107778 poschodia_a_studenti  
total 21  free 4  backup 5  lts 0 max-misbal 1

and when I restart test client several times within say few hours it 
gets same ip address it had few restarts ago. It is even asking in DHCP 
DISCOVER message for its current ip address but the server decides to 
lease another one (no DHCP NAK message). The default and max lease times 
for these clients are both set to 2592000.

These are records in dhcpd.leases when I restart test client (those log 
lines are perhaps my misconfiguration in dhcpd.conf or what, but I had 
this issue even before I added logging so it's not related):

lease XXX.XXX.XXX.232 {
   starts 3 2017/06/28 07:29:45;
   ends 3 2017/06/28 08:28:38;
   tstp 3 2017/06/28 08:28:38;
   tsfp 6 2017/08/12 07:29:45;
   cltt 3 2017/06/28 07:29:45;
   binding state released;
   next binding state free;
   hardware ethernet aa:bb:cc:dd:ee:ff;
   client-hostname "vm102";
}
lease XXX.XXX.XXX.232 {
   starts 3 2017/06/28 07:29:45;
   ends 3 2017/06/28 08:28:38;
   tstp 3 2017/06/28 08:28:38;
   tsfp 3 2017/06/28 08:28:38;
   atsfp 3 2017/06/28 08:28:38;
   cltt 3 2017/06/28 07:29:45;
   binding state free;
   hardware ethernet aa:bb:cc:dd:ee:ff;
}
lease XXX.XXX.XXX.231 {
   starts 3 2017/06/28 08:29:03;
   ends 3 2017/06/28 08:59:03;
   tstp 5 2017/07/28 08:44:03;
   tsfp 3 2017/06/28 08:08:55;
   cltt 3 2017/06/28 08:29:03;
   binding state active;
   next binding state expired;
   hardware ethernet aa:bb:cc:dd:ee:ff;
   set mac_6 = "02";
   client-hostname "vm102";
   on release {
     log (error, "=============[ START COMMIT ]================");
     log (error, "host-decl-name: ");
     log (error, host-decl-name);
     log (error, "option host-name: ");
     log (error,
         option host-name);
     log (error, "config-option server.ddns-hostname: ");
     log (error,
         option host-name);
     log (error, "config-option server.ddns-hostname: ");
     log (error,
         config-option server.ddns-hostname);
     log (error, "============[ END COMMIT ]==================");
   }
}
lease XXX.XXX.XXX.231 {
   starts 3 2017/06/28 08:29:03;
   ends 3 2017/06/28 08:59:03;
   tstp 5 2017/07/28 08:44:03;
   tsfp 3 2017/06/28 08:08:55;
   cltt 3 2017/06/28 08:29:03;
   binding state active;
   next binding state expired;
   hardware ethernet aa:bb:cc:dd:ee:ff;
   set ddns-txt = "000b7fa68b3f8b2e4967e49ff0faef4cf6";
   set ddns-fwd-name = "vm102.some.domain.";
   set mac_6 = "02";
   client-hostname "vm102";
   on release {
     log (error, "=============[ START COMMIT ]================");
     log (error, "host-decl-name: ");
     log (error, host-decl-name);
     log (error, "option host-name: ");
     log (error,
         option host-name);
     log (error, "config-option server.ddns-hostname: ");
     log (error,
         config-option server.ddns-hostname);
     log (error, "============[ END COMMIT ]==================");
   }
}
lease XXX.XXX.XXX.231 {
   starts 3 2017/06/28 08:29:03;
   ends 3 2017/06/28 08:59:03;
   tstp 5 2017/07/28 08:44:03;
   tsfp 3 2017/06/28 08:08:55;
   cltt 3 2017/06/28 08:29:03;
   binding state active;
   next binding state expired;
   binding state active;
   next binding state expired;
   hardware ethernet aa:bb:cc:dd:ee:ff;
   set ddns-rev-name = "231.XXX.XXX.XXX.in-addr.arpa.";
   set ddns-txt = "000b7fa68b3f8b2e4967e49ff0faef4cf6";
   set ddns-fwd-name = "vm102.some.domain.";
   set mac_6 = "02";
   client-hostname "vm102";
   on release {
     log (error, "=============[ START COMMIT ]================");
     log (error, "host-decl-name: ");
     log (error, host-decl-name);
     log (error, "option host-name: ");
     log (error,
         option host-name);
     log (error, "config-option server.ddns-hostname: ");
     log (error,
         config-option server.ddns-hostname);
     log (error, "============[ END COMMIT ]==================");
   }
}
lease XXX.XXX.XXX.231 {
   starts 3 2017/06/28 08:29:03;
   ends 3 2017/06/28 08:59:03;
   tstp 5 2017/07/28 08:44:03;
   tsfp 5 2017/07/28 08:44:03;
   atsfp 5 2017/07/28 08:44:03;
   cltt 3 2017/06/28 08:29:03;
   binding state active;
   next binding state expired;
   hardware ethernet aa:bb:cc:dd:ee:ff;
   set ddns-rev-name = "231.XXX.XXX.XXX.in-addr.arpa.";
   set ddns-txt = "000b7fa68b3f8b2e4967e49ff0faef4cf6";
   set ddns-fwd-name = "vm102.some.domain.";
   set mac_6 = "02";
   client-hostname "vm102";
   on release {
     log (error, "=============[ START COMMIT ]================");
     log (error, "host-decl-name: ");
     log (error, host-decl-name);
     log (error, "option host-name: ");
     log (error,
         option host-name);
     log (error, "config-option server.ddns-hostname: ");
     log (error,
         config-option server.ddns-hostname);
     log (error, "============[ END COMMIT ]==================");
   }
}

Do you see anything wrong there?

Thanks for any insights, Rado.