Red Hat Enterprise Linux 5 Administration Unleashed

324CHAPTER 14Granting Network Connectivity with DHCPTABLE 14.1 ContinuedCommandhardware fixed-address DescriptionSpecify the hardware address of a client such as the MACaddress of an Ethernet card. can be eitherethernet or token-ring.IP address that should be assigned to a specific host. Onlyvalid within a host declaration.After a client has successfully leased an IP address from the server, that IP address isreserved for the MAC address of the client for a specific amount of time as determined bya combination of the default-lease-time, maximum-lease-time, and minimum-lease-timeparameters. This information is recorded in the /var/lib/dhcp/dhcpd.leases file on theDHCP server to make sure an IP address isn’t assigned to more than one system at thesame time.NOTEFor DHCP client configuration, refer to Chapter 2, which provides instructions fornetwork configuration.Starting and Stopping the ServerLike the other services in Red Hat Enterprise Linux, DHCP can be started, stopped, andrestarted with the service command as root. To start the server, use the service dhcpdstart command. Each time the server is started, it looks for the /var/lib/dhcp/dhcpd.leases file. If it is not found, the service is not started. Before the service is started for thefirst time, the file must be created with the command touch /var/lib/dhcp/dhcpd.leases.The command service dhcpd status displays whether the service is running. Thecommand service dhcpd restart restarts the service, including re-reading the configurationfile. Remember that the dhcpd service must be restarted after the configuration file ismodified.To configure the DHCP service to start automatically at boot time, use the command:chkconfig dhcpd onThe DHCP server also looks for the /etc/sysconfig/dhcpd configuration file on startup. Itis not required, but it can be used to define command-line options to dhcpd. The defaultfile contains the following lines:# Command line options hereDHCPDARGS=For example, to only listen for connections on a specific network interface:DHCPDARGS=eth0