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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[6] should recognize it and prompt for the configuration of the corresponding kernel module for it. Be sure to check the Hardware Compatibility List available at If the network card is not configured by the installation program or Kudzu and you know which kernel module to load for it, refer to Chapter 37, Kernel Modules for details on loading kernel modules.
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:
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:
A configuration file is needed for each device to be configured to use DHCP.
Other options for the network script include:
  • DHCP_HOSTNAME — Only use this option if the DHCP server requires the client to specify a hostname before receiving an IP address. (The DHCP server daemon in Red Hat Enterprise Linux does not support this feature.)
  • PEERDNS=<answer> , where <answer> is one of the following:
    • yes — Modify /etc/resolv.conf with information from the server. If using DHCP, then yes is the default.
    • no — Do not modify /etc/resolv.conf.
  • SRCADDR=<address> , where <address> is the specified source IP address for outgoing packets.
  • USERCTL=<answer> , where <answer> is one of the following:
    • yes — Non-root users are allowed to control this device.
    • no — Non-root users are not allowed to control this device.
If you prefer using a graphical interface, refer to Chapter 17, Network Configuration for details on using the Network Administration Tool to configure a network interface to use DHCP.


For advanced configurations of client DHCP options such as protocol timing, lease requirements and requests, dynamic DNS support, aliases, as well as a wide variety of values to override, prepend, or append to client-side configurations, refer to the dhclient and dhclient.conf man pages.

[6] Kudzu is a hardware probing tool run at system boot time to determine what hardware has been added or removed from the system.