Final answer:
If a client requests an already assigned IP address during DHCP lease negotiation, the server must offer a different IP address and continue the negotiation process with a DHCP Offer message to maintain unique IP address assignment.
Step-by-step explanation:
During DHCP lease negotiation, if a client requests an IP address that the server has already assigned, the server will not confirm the lease and must offer a different IP address. The server maintains a database of allocated IP addresses to avoid such conflicts. If the requested IP address is no longer available, the server will select a new IP address and send a DHCP Offer message with the new address to the client. The client can then send a DHCP Request message for the new IP address, continuing the negotiation process. This mechanism ensures that IP addresses are uniquely assigned to avoid networking conflicts.