IP address lease extension

The IP address dynamically allocated by a DHCP server to a client has a lease. When the lease expires, the IP address is reclaimed by the DHCP server. To continue using the IP address, the client must extend the lease duration.

After half the lease duration, the DHCP client sends a DHCP-REQUEST unicast to the DHCP server to extend the lease. Depending on availability of the IP address, the DHCP server returns either a DHCP-ACK unicast confirming that the client's lease has been extended, or a DHCP-NAK unicast denying the request.

If the client receives no reply, it broadcasts another DHCP-REQUEST message for lease extension after 7/8 lease duration. Again, depending on availability of the IP address, the DHCP server returns either a DHCP-ACK unicast confirming that the client's lease has been extended, or a DHCP-NAK unicast denying the request.