On a GNU/Linux server locate the files dhcpd.leases and dhcpd.leases~
Mine is a Debian so the location is /var/lib/dhcpd3/ .
- delete the temporary file dhcpd.leases~:
$ sudo rm dhcpd.leases~
- flush the lease cache dhcpd.leases:
$ sudo echo "" > dhcpd.leases
the next time the clients will request a lease they will probably obtain a different IP respect the one they had before.
