Configuring A Dhcp Server; Configuration File - Red Hat ENTERPRISE LINUX 5 - DEPLOYMENT Deployment Manual

Chapter 21.
Dynamic Host Configuration Protocol
(DHCP)
Dynamic Host Configuration Protocol (DHCP) is a network protocol that automatically assigns TCP/
IP information to client machines. Each DHCP client connects to the centrally located DHCP server,
which returns that client's network configuration (including the IP address, gateway, and DNS servers).
21.1. Why Use DHCP?
DHCP is useful for automatic configuration of client network interfaces. When configuring the client
system, the administrator chooses DHCP instead of specifying an IP address, netmask, gateway, or
DNS servers. The client retrieves this information from the DHCP server. DHCP is also useful if an
administrator wants to change the IP addresses of a large number of systems. Instead of reconfiguring
all the systems, he can just edit one DHCP configuration file on the server for the new set of IP
addresses. If the DNS servers for an organization changes, the changes are made on the DHCP
server, not on the DHCP clients. When the administrator restarts the network or reboots the clients,
the changes will go into effect.
If an organization has a functional DHCP server properly connected to a network, laptops and other
mobile computer users can move these devices from office to office.

21.2. Configuring a DHCP Server

The dhcp package contains an ISC DHCP server. First, install the package as the superuser:
~]# yum install dhcp
Installing the dhcp package creates a file, /etc/dhcpd.conf, which is merely an empty

configuration file:

~]# cat /etc/dhcpd.conf
#
# DHCP Server Configuration file.
# see /usr/share/doc/dhcp*/dhcpd.conf.sample
The sample configuration file can be found at /usr/share/doc/dhcp-<version>/
dhcpd.conf.sample. You should use this file to help you configure /etc/dhcpd.conf, which is
explained in detail below.
DHCP also uses the file /var/lib/dhcpd/dhcpd.leases to store the client lease database. Refer
Section 21.2.2, "Lease Database"
to for more information.
21.2.1. Configuration File
The first step in configuring a DHCP server is to create the configuration file that stores the network
information for the clients. Use this file to declare options and global options for client systems.
The configuration file can contain extra tabs or blank lines for easier formatting. Keywords are case-
insensitive and lines beginning with a hash mark (#) are considered comments.
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