Red Hat ENTERPRISE LINUX 5 - VIRTUAL SERVER ADMINISTRATION, Руководство по развертыванию

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Chapter 21. Dynamic Host Configuration Protocol (DHCP)
298
Other command line options that can be specified in
/etc/sysconfig/dhcpd
include:
•
-p <portnum>
— Specifies the UDP port number on which
dhcpd
should listen. The default is
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 21.2.4, “DHCP Relay Agent”
for details.
•
-f
— Runs the daemon as a foreground process. This is mostly used for debugging.
•
-d
— Logs 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>
— Specifies the location of the configuration file. The default location is
/etc/
dhcpd.conf
.
•
-lf <filename>
— Specifies 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/dhcpd/dhcpd.leases
.
•
-q
— Do not print the entire copyright message when starting the daemon.
21.2.4. 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
.
21.3. 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
1
will recognize it and
prompt you for the proper kernel module (Be sure to check the Hardware Compatibility List at
http://
hardware.redhat.com/hcl/
). If either the installation program or kudzu does not recognize the network
card, you can load the correct kernel module (refer to
Chapter 41, General Parameters and Modules
for details).
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-
Kudzu
is a hardware probing tool run at system boot time to determine what hardware has been added or removed from the
system.