DHCP 运用了UDP

DHCP uses UDP as its transport protocol. DHCP messages from a client to a server are
sent to the DHCP server port (UDP port 67),　and DHCP messages from a server to a
client are sent to the DHCP client port (UDP port 68).

The client broadcasts a
DHCPDISCOVER message on its local physical subnet. The DHCPDISCOVER message
may include options that suggest values for the network address and lease duration.
BOOTP relay agents may pass the message on to DHCP servers not on the same physical
subnet.

Each server may respond with a DHCPOFFER message that includes an available
network address in the "ipaddr" field (and other configuration parameters in DHCP
options). Servers need not reserve the offered network address, although the protocol will
work more efficiently if the server avoids allocating the offered network address to
another client. The server unicasts the DHCPOFFER message to the client (using the
DHCP/BOOTP relay agent if necessary) if possible, or may broadcast the message to a
broadcast address (preferably 255.255.255.255) on the client's subnet.Incorrect Answers:
C. DHCP messages are broadcast to the "all hosts" address. IP multicast addresses are not
used.