על רגל אחת:
Per the DHCP standard, RFC 2131, a DHCP client does not wait for its lease to expire, because it risks getting a new address assigned to it. Instead, when a DHCP client reaches the halfway point of its lease period, it attempts to extend its lease so that it retains the same IP address. Thus, the lease duration is like a sliding window.
Typically if an IP address was assigned to a device, the device was subsequently taken off the network and its lease was not extended, the DHCP server will let that lease run out. Because the client is gone from the network and no longer needs the address, the lease duration in the server is reached and the lease is in “Expired” state.