ISC Dhcpd Duplicate UID Lease

Someone asked this question in one of his blog posts:

Ever see this?

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

Yes, I’m seeing something like that now in the my dhdcp logs. Here is the actual message:

DHCPREQUEST for 192.168.1.109 from 08:00:27:6e:61:b8 via eth0
DHCPACK on 192.168.1.109 to 08:00:27:6e:61:b8 via eth0
DHCPINFORM from 192.168.1.109 via eth0
DHCPACK to 192.168.1.109 (08:00:27:6e:61:b8) via eth0
uid lease 192.168.1.224 for client 08:00:27:6e:61:b8 is duplicate on 192.168.1.0/24
DHCPREQUEST for 192.168.1.109 from 08:00:27:6e:61:b8 via eth0
DHCPACK on 192.168.1.109 to 08:00:27:6e:61:b8 via eth0

I think I know why this happened. Basically, the machine with MAC address of ’08:00:27:6e:61:b8′ used to have grab an IP address

from the pool. Then later on, I have created a reservation for it.

host mathtXXX-win {
    hardware ethernet 08:00:27:6e:61:b8;
    fixed-address 192.168.1.109;
}

On Centos 7, the lease file is located at: /var/lib/dhcpd/dhcpd.leases. Here’s the duplicated lease for mathtXXX:

lease 192.168.1.224 {
  starts 3 2015/06/10 01:44:21;
  ends 3 2015/06/10 01:49:24;
  tstp 3 2015/06/10 01:49:24;
  cltt 3 2015/06/10 01:44:21;
  binding state free;
  hardware ethernet 08:00:27:6e:61:b8;
  uid "\001\010\000'na\270";
}

By removing the above block and restarting dhcpd service, the “uid lease duplicate” message no longer appears in the log.