PLANET WGSW-52040 - Manual (Page 253)

Chapter 31 DHCP Configuration
31.1 Introduction to DHCP
DHCP [RFC2131] is the acronym for Dynamic Host Configuration Protocol. It is a protocol that
assigns IP address dynamically from the address pool as well as other network configuration
parameters such as default gateway, DNS server, and default route and host image file
position within the network. DHCP is the enhanced version of BOOTP. It is a mainstream
technology that can not only provide boot information for diskless workstations, but can also
release the administrators from manual recording of IP allocation and reduce user effort and
cost on configuration. Another benefit of DHCP is it can partially ease the pressure on IP
demands, when the user of an IP leaves the network that IP can be assigned to another user.
DHCP is a client-server protocol, the DHCP client requests the network address and
configuration parameters from the DHCP server; the server provides the network address and
configuration parameters for the clients; if DHCP server and clients are located in different
subnets, DHCP relay is required for DHCP packets to be transferred between the DHCP client
and DHCP server. The implementation of DHCP is shown below:
Figure 31-1: DHCP protocol interaction
Explanation:
Discover
Offer
Request
Ack
DHCP SERVER
DHCP CLIENT
1． DHCP client broadcasts DHCPDISCOVER packets in the local subnet.
2． On receiving the DHCPDISCOVER packet, DHCP server sends a DHCPOFFER packet
along with IP address and other network parameters to the DHCP client.
3． DHCP client broadcast DHCPREQUEST packet with the information for the DHCP server
it selected after selecting from the DHCPOFFER packets.
4． The DHCP server selected by the client sends a DHCPACK packet and the client gets an
IP address and other network configuration parameters.
The above four steps finish a Dynamic host configuration assignment process. However, if the
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