Specifications

82 Chapter 4. Configuring Special Features
DHCP (Dynamic Host ConÞguration Protocol)
The router supports DHCP and can act as the DHCP server. (The routerÕs DHCP server disables itself if it locates
other active DHCP servers on the network or if a DHCP server on the WAN has been explicitly specified.)
This section describes how to configure DHCP using the Command Line Interface. Configuring DHCP can be a
complex process; this section is therefore intended for network managers. For a complete list and explanation of
the DHCP commands, see DHCP Commands, page 309.
Note: Some DHCP values can be set using the Windows Quick Start application, the Windows Configuration
Manager, or the web-based EZ Setup application.
DHCP Address Allocation
DHCP is a service that allocates IP addresses automatically to any DHCP client requesting an IP address. (A
DHCP client can be any device attached to your network, for example, a PC.) It can also provide option values
(such as the subnet mask, DNS, and gateway values) automatically.
Using DHCP to automatically acquire initialization parameters translates into avoiding the more involved router/
PC manual initialization process. (The manual initialization requires reconfiguration of router and/or PC addresses
to be in the same network.)
To configure DHCP for a network, the network administrator defines a range of valid IP addresses to be used in
the subnetwork as well as options and other parameters. This process is described in the next section, DHCP
Administration and Configuration.
Note 1: DHCP will work only if the TCP/IP stack is installed on the PCs.
Note 2: In Windows, DHCP is enabled by selecting it on your PC (under Settings, Control Panel, Network, and
TCP/IP in the Configuration tab page).
DHCP Client Requests
Before becoming active, the routerÕs DHCP server attempts to locate other active DHCP servers on the network,
such as Windows NT servers. If one is detected, the routerÕs DHCP server disables itself.
When the WAN link activates and the source IP address or mask is undefined (i.e. 0.0.0.0), the router places a
DHCP client request over the WAN link. The router may learn the following parameters:
¥ DNS address
¥ Default gateway
¥ Syslog server IP address
¥ Time server IP address
¥ Source IP address to use
To see the gateway and source IP addresses that were returned, use the iproutes command.
The IP addresses and options assigned to a client are collectively called the ÒleaseÓ. The lease is only valid for a
certain period of time and is automatically renewed by the client.