Configuring A Dhcp Client - Red Hat ENTERPRISE LINUX 3 System Administration Manual

Chapter 25. Dynamic Host Configuration Protocol (DHCP)
To start the DHCP service, use the command
server, use the command
matically at boot time, refer to Chapter 21 Controlling Access to Services for information on how to
manage services.
If more than one network interface is attached to the system, but the DHCP server should only be
started on one of the interface, configure the DHCP server to start only on that device. In
/etc/sysconfig/dhcpd
# Command line options here
DHCPDARGS=eth0
This is useful for a firewall machine with two network cards. One network card can be configured as a
DHCP client to retrieve an IP address to the Internet. The other network card can be used as a DHCP
server for the internal network behind the firewall. Specifying only the network card connected to the
internal network makes the system more secure because users can not connect to the daemon via the
Internet.
Other command line options that can be specified in
• -p < portnum >
port 67. The DHCP server transmits responses to the DHCP clients at a port number one greater
than the udp port specified. For example, if the default port 67 is used, the server listens on port 67
for requests and responses to the client on port 68. If a port is specified here and the DHCP relay
agent is used, the same port on which the DHCP relay agent should listen must be specified. Refer
to Section 25.2.4 DHCP Relay Agent for details.
— Run the daemon as a foreground process. This is mostly used for debugging.
•
-f
— Log the DHCP server daemon to the standard error descriptor. This is mostly used for de-
•
-d
bugging. If this is not specified, the log is written to
•
-cf < filename >
/etc/dhcpd.conf
• -lf < filename >
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
— Do not print the entire copyright message when starting the daemon.
• -q
25.2.4. DHCP Relay Agent
The DHCP Relay Agent (
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
To start the DHCP Relay Agent, use the command
/sbin/service dhcpd stop
, add the name of the interface to the list of
— Specify the udp port number on which
— Specify the location of the configuration file. The default location is
.
— Specify the location of the lease database file. If a lease database file already
/var/lib/dhcp/dhcpd.leases
) allows for the relay of DHCP and BOOTP requests from a
dhcrelay
with the
/sbin/service dhcpd start
. To configure the daemon to start auto-
/etc/sysconfig/dhcpd
/var/log/messages
directive.
INTERFACES
service dhcrelay start
. To stop the DHCP
:
DHCPDARGS
include:
should listen. The default is
dhcpd
.
.
.
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