Das hier erklärt es eigentlich ganz gut:
How does DHCP work?DHCP works by leasing IP addresses and IP information to network clients for a period of time. For the lease to happen, the following negotiation process occurs:
1. During the boot process, a client computer that is configured as a DHCP client sends out a broadcast packet called DHCPDISCOVER. This Discover packet contains the client’s computer name and Media Access Control (MAC) address so the DHCP servers can respond to it. Basically, the Discover packet says, “I’m looking for a DHCP server who can lease an IP address.”
2. DHCP servers on the network respond to the broadcast with a DHCPOFFER. In essence, the DHCPOFFER says, “I am a DHCP server and I have a lease for you.” If several DHCP servers respond to the request, the client accepts the first offer that it receives.
3. The client responds via a broadcast message called a DHCPREQUEST. This message basically says, “I accept your lease offer and would like an IP address.” If other DHCP servers made offers, they also see their lease offers were not accepted by the broadcast message, so they rescind their offers. (They must not like getting snubbed by a client computer.)
4. The DHCP server whose offer was accepted responds with a DHCPACK message, which acknowledges the lease acceptance and contains the client’s IP address lease as well as other IP addressing information that you configure the server to provide. The client is now a TCP/IP client and can participate on the network.