Your PC connects to a LAN and uses DHCP to lease an IP address for the first time. Of the usual four DHCP messages that flow between the PC (DHCP client) and the DHCP server, which ones do the server send? (Choose two answers)

(A) Acknowledgment
(B) Request
(C) Offer
(D) Discover

A and C is the correct answer.

DHCP uses the following four messages between the client and the server:

1. Discover: Sent by the DHCP client to find a willing DHCP server.
2. Offer: Sent by a DHCP server to offer to lease to that client a specific IP address (and inform the client of its other parameters).
3. Request: Sent by the DHCP client to ask the server to lease the IPv4 address listed in the Offer message.
4. Acknowledgment: Sent by the DHCP server to assign the address and to list the mask, default router, and DNS server IP addresses.

DHCP clients have a problem, they do not have an IP address yet, but they need to send these DHCP messages inside IP packets. To make that work, DHCP messages make use of two special IPv4 addresses that allow a host that has no IP address to still be able to send and receive messages on the local subnet:

• 0.0.0.0: An address reserved for use as a source IPv4 address for hosts that do not yet have an IP address.
• 255.255.255.255: The local broadcast IP address. Packets sent to this destination address are broadcast on the local data link, but routers do not forward them.