Dhcp Relay Agent; Configuring A Dhcp Client - Red Hat ENTERPRISE LINUX 4 System Administration Manual

Chapter 23. Dynamic Host Configuration Protocol (DHCP)
• -d — Log the DHCP server daemon to the standard error descriptor. This is mostly used for
debugging. If this is not specified, the log is written to /var/log/messages.
• -cf <filename> — Specify the location of the configuration file. The default location is /etc/
dhcpd.conf.
• -lf <filename> — Specify the location of the lease database file. If a lease database file already
exists, it is very important that the same file be used every time the DHCP server is started. It is
strongly recommended that this option only be used for debugging purposes on non-production
machines. The default location is /var/lib/dhcp/dhcpd.leases.
• -q — Do not print the entire copyright message when starting the daemon.

23.2.4. DHCP Relay Agent

The DHCP Relay Agent (dhcrelay) allows for the relay of DHCP and BOOTP requests from a subnet
with no DHCP server on it to one or more DHCP servers on other subnets.
When a DHCP client requests information, the DHCP Relay Agent forwards the request to the list of
DHCP servers specified when the DHCP Relay Agent is started. When a DHCP server returns a reply,
the reply is broadcast or unicast on the network that sent the original request.
The DHCP Relay Agent listens for DHCP requests on all interfaces unless the interfaces are specified
in /etc/sysconfig/dhcrelay with the INTERFACES directive.
To start the DHCP Relay Agent, use the command service dhcrelay start.

23.3. Configuring a DHCP Client

The first step for configuring a DHCP client is to make sure the kernel recognizes the network interface
card. Most cards are recognized during the installation process and the system is configured to use
the correct kernel module for the card. If a card is added after installation, Kudzu
it and prompt for the configuration of the corresponding kernel module for it. Be sure to check the
Hardware Compatibility List available at http://hardware.redhat.com/hcl/. If the network card is not
configured by the installation program or Kudzu and you know which kernel module to load for it, refer
Chapter 37, Kernel Modules
to
To configure a DHCP client manually, modify the /etc/sysconfig/network file to enable
networking and the configuration file for each network device in the /etc/sysconfig/network-
scripts directory. In this directory, each device should have a configuration file named ifcfg-
eth0, where eth0 is the network device name.
The /etc/sysconfig/network file should contain the following line:
NETWORKING=yes
The NETWORKING variable must be set to yes if you want networking to start at boot time.
The /etc/sysconfig/network-scripts/ifcfg-eth0 file should contain the following lines:
Kudzu is a hardware probing tool run at system boot time to determine what hardware has been added or removed from the
system.
230
for details on loading kernel modules.
1
should recognize