3Com Switch 8800 Configuration Guide Chapter 13 DHCP Configuration
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Chapter 13 DHCP Configuration 13.1 Introduction to DHCP
13.1.1 How DHCP Works
This is a world where networks are ever-growing in both size and complexity, and the
network configuration is getting more and more complex. As is often the case, the
number of hosts in a network exceeds that of the available IP addresses, and position
changes of hosts (when users carry their laptops from here to there, or move to a
wireless network) require reassigned new IP addresses. Dynamic host configuration
protocol (DHCP) is designed to accommodate this context. DHCP adopts client/server
model, where DHCP clients send requests to the DHCP server dynamically and the
DHCP server in turn returns corresponding configuration information (such as IP
addresses) according to the policies configured for it.
A typical DHCP implementation comprises a DHCP server and multiple DHCP clients
(PCs or laptops). Figure 13-1 illustrates a network that employs DHCP.
LAN
DHCP Server
DHCP Client DHCP Client
DHCP Client DHCP Client
Figure 13-1 Network diagram for DHCP
I. IP address assignment
1) IP address assignment policy
Different types of clients have different requirements for IP addresses. Servers usually
require long-term fixed IP addresses, some hosts may require automatically assigned
long-term fixed IP addresses , and some hosts may only require dynamically assigned
temporary IP addresses.
A DHCP server provides three policies to meet these requirements.
z Manual IP address assignment. The administrator assigns fixed IP addresses to
DHCP clients that are of special uses, such as a WWW server.