ISC DHCP server config option one-lease-per-client
The one-lease-per-client statement
If this flag is enabled, whenever a client sends a DHCPREQUEST for a particular lease, the server will automatically free any other leases the client holds. This presumes that when the client sends a DHCPRE- QUEST, it has forgotten any lease not mentioned in the DHCPREQUEST - i.e., the client has only a single network interface and it does not remember leases it's holding on networks to which it is not currently attached. Neither of these assumptions are guaranteed or provable, so we urge caution in the use of this statement.
Dubious utility: put here only for documentation purpose.