DHCP Duplicate IPs

[Nathan McDavit-Van Fleet]

We are having some issues with duplicates in the system where clients might
have two IPs in the dhcp leases, even on the same subnet. We only allow
one-ip-per-client but there appears to be duplicates since we started
getting this error:

"dhcpd: uid lease 192.168.1.150 for client xx:xx:xx:xx:xx:xx is duplicate on
192.168.1/24"

I think it might have to do with the servers being out of synchronization.
So the client gets an IP from the low range of the subnet from server A and
then one IP from the high range from server B. It's odd because I get very
persistent errors about sync refusal that never resolve (dhcp-failover
rejected: incoming update is less critical than outgoing update). 

I did some online research and came across this page:
"http://www.culmination.org/2008/10/28/isc-dhcpd-duplicate-uid-lease/". I
noticed that there is a suggestion in the comments to include "deny
duplicates;" in the dhcpd.conf. It appears to work as expected, but I'm not
sure if this is just covering up the real problem and not actually
correcting it. We're still getting the same error, but it does not appear to
repeat for the same user. So I hope that it's keeping the dhcpd.leases file
clean of conflicts?


Detailed log for one user
Jan 12 07:22:30 shining dhcpd: DHCPREQUEST for 192.168.2.11 from
00:bb:aa:cc:00:bb:aa:cc via 10.106.155.3: wrong network.
Jan 12 07:22:30 shining dhcpd: DHCPNAK on 192.168.2.11 to
00:bb:aa:cc:00:bb:aa:cc via 10.106.155.3
Jan 12 07:22:30 shining dhcpd: DHCPDISCOVER from 00:bb:aa:cc:00:bb:aa:cc via
10.106.155.3: load balance to peer iits-dhcp-failover
Jan 12 07:48:47 shining dhcpd: DHCPDISCOVER from 00:bb:aa:cc:00:bb:aa:cc via
10.106.228.1
Jan 12 07:48:48 shining dhcpd: DHCPOFFER on 10.106.229.128 to
00:bb:aa:cc:00:bb:aa:cc (DTiPod) via 10.106.228.1
Jan 12 07:48:49 shining dhcpd: DHCPREQUEST for 10.106.229.128 (10.106.101.3)
from 00:bb:aa:cc:00:bb:aa:cc (DTiPod) via 10.106.228.1
Jan 12 07:48:49 shining dhcpd: DHCPACK on 10.106.229.128 to
00:bb:aa:cc:00:bb:aa:cc (DTiPod) via 10.106.228.1
Jan 12 08:02:31 shining dhcpd: DHCPREQUEST for 10.106.229.128 from
00:bb:aa:cc:00:bb:aa:cc (DTiPod) via 10.106.228.1
Jan 12 08:02:31 shining dhcpd: DHCPACK on 10.106.229.128 to
00:bb:aa:cc:00:bb:aa:cc (DTiPod) via 10.106.228.1
Jan 12 08:05:23 shining dhcpd: DHCPREQUEST for 10.106.229.128 from
00:bb:aa:cc:00:bb:aa:cc (DTiPod) via 10.106.155.3: wrong network.
Jan 12 08:05:23 shining dhcpd: DHCPNAK on 10.106.229.128 to
00:bb:aa:cc:00:bb:aa:cc via 10.106.155.3
Jan 12 08:05:23 shining dhcpd: DHCPDISCOVER from 00:bb:aa:cc:00:bb:aa:cc via
10.106.155.3: load balance to peer iits-dhcp-failover
Jan 12 08:26:31 shining dhcpd: DHCPDISCOVER from 00:bb:aa:cc:00:bb:aa:cc via
10.106.155.3
Jan 12 08:26:32 shining dhcpd: DHCPOFFER on 10.106.155.203 to
00:bb:aa:cc:00:bb:aa:cc (DTiPod) via 10.106.155.3
Jan 12 08:26:33 shining dhcpd: DHCPREQUEST for 10.106.155.203 (10.106.101.3)
from 00:bb:aa:cc:00:bb:aa:cc (DTiPod) via 10.106.155.3
Jan 12 08:26:33 shining dhcpd: DHCPACK on 10.106.155.203 to
00:bb:aa:cc:00:bb:aa:cc (DTiPod) via 10.106.155.3
Jan 12 08:29:29 shining dhcpd: DHCPREQUEST for 10.106.155.203 from
00:bb:aa:cc:00:bb:aa:cc (DTiPod) via 10.106.228.1: wrong network.
Jan 12 08:29:29 shining dhcpd: DHCPNAK on 10.106.155.203 to
00:bb:aa:cc:00:bb:aa:cc via 10.106.228.1
Jan 12 08:29:29 shining dhcpd: DHCPDISCOVER from 00:bb:aa:cc:00:bb:aa:cc via
10.106.228.1: load balance to peer iits-dhcp-failover
Jan 12 08:29:32 shining dhcpd: uid lease 10.106.229.128 for client
00:bb:aa:cc:00:bb:aa:cc is duplicate on 10.106.228.0/23
Jan 12 08:29:32 shining dhcpd: DHCPREQUEST for 10.106.229.115
(10.106.140.240) from 00:bb:aa:cc:00:bb:aa:cc via 10.106.228.1: lease owned
by peer
Jan 12 09:00:51 shining dhcpd: DHCPDISCOVER from 00:bb:aa:cc:00:bb:aa:cc via
10.106.228.1: load balance to peer iits-dhcp-failover
Jan 12 09:00:53 shining dhcpd: uid lease 10.106.229.128 for client
00:bb:aa:cc:00:bb:aa:cc is duplicate on 10.106.228.0/23
Jan 12 09:00:53 shining dhcpd: DHCPREQUEST for 10.106.229.149
(10.106.140.240) from 00:bb:aa:cc:00:bb:aa:cc via 10.106.228.1: lease owned
by peer
Regards,

Nathan Van Fleet