Dynamic IP address allocation process

The client broadcasts a DHCP-DISCOVER message to locate a DHCP server.

A DHCP server offers configuration parameters, such as an IP address to the client in a DHCP-OFFER message. The sending mode of the DHCP-OFFER message is determined by the flag field in the DHCP-DISCOVER message. For related information, see "DHCP message format."

If several DHCP servers send offers to the client, the client accepts the first received offer, and broadcasts it in a DHCP-REQUEST message to formally request the IP address.

All DHCP servers receive the DHCP-REQUEST message, but only the server from which the client accepts the offered IP address returns a DHCP-ACK message to the client, confirming that the IP address has been allocated to the client, or a DHCP-NAK message, denying the IP address allocation.

	NOTE: After the client receives the DHCP-ACK message, it broadcasts a gratuitous ARP packet to verify whether the IP address assigned by the server is already in use. If the client receives no response within the specified time, the client uses the assigned IP address. Otherwise, the client sends a DHCP-DECLINE message to the server and requests an IP address again. IP addresses offered by other DHCP servers are still assignable to other clients.