The dhcp (Dynamic Host Configuration Protocol) package contains an Internet Systems Consortium (ISC) DHCP server. DHCP is used to assign IP addresses and other stuff like gateway and DNS details automatically to the clients. we need a DHCP server configured for offering ipaddress to the clients when it is required. First, install the package as the superuser:
# yum install dhcp
Installing the dhcp package creates a file, /etc/dhcp/dhcpd.conf, which is merely an empty configuration file:
cat /etc/dhcp/dhcpd.conf
#
# DHCP Server Configuration file.
# see /usr/share/doc/dhcp*/dhcpd.conf.sample
The sample configuration file can be found at /usr/share/doc/dhcp-<version>/dhcpd.conf.sample. You should use this file to help you configure /etc/dhcp/dhcpd.conf, which is explained in detail below.
DHCP also uses the file
/var/lib/dhcpd/dhcpd.leases to store the client lease database.
After installing dhcp server packages along with dependencies .Assign a static ip (eg: “192.168.0.254″) in the same DHCP range for the listening interface ( eg : “eth0″ ). Open/etc/sysconfig/network-scripts/ifcfg-eth0 file and make the changes as per your requirement.
Configuration File
The first step in configuring a DHCP server is to create the configuration file that stores the network information for the clients. Use this file to declare options and global options for client systems.
For every subnet which will be served, and for every subnet to which the DHCP server is connected, there must be one subnet declaration, which tells the DHCP daemon how to recognize that an address is on that subnet. A subnet declaration is required for each subnet even if no addresses will be dynamically allocated to that subnet.
In this example, there are global options for every DHCP client in the subnet and a
range declared. Clients are assigned an IP address within the range.
subnet 192.168.1.0 netmask 255.255.255.0 {
option routers 192.168.1.254;
option subnet-mask 255.255.255.0;
option domain-search "example.com";
option domain-name-servers 192.168.1.1;
option time-offset -18000; # Eastern Standard Time
range 192.168.1.10 192.168.1.100;
}
To configure a DHCP server that leases a dynamic IP address to a system within a subnet, modify Range parameter with your values. It declares a default lease time, maximum lease time, and network configuration values for the clients. This example assigns IP addresses in the
range 192.168.1.10 and 192.168.1.100 to client systems.
default-lease-time 600;
max-lease-time 7200;
option subnet-mask 255.255.255.0;
option broadcast-address 192.168.1.255;
option routers 192.168.1.254;
option domain-name-servers 192.168.1.1, 192.168.1.2;
option domain-search "example.com";
subnet 192.168.1.0 netmask 255.255.255.0 {
range 192.168.1.10 192.168.1.100;
}
To assign an IP address to a client based on the MAC address of the network interface card, use the hardware ethernet parameter within a host declaration. As demonstrated below, the host apex declaration specifies that the network interface card with the MAC address 00:A0:78:8E:9E:AA always receives the IP address 192.168.1.4.
Note that you can also use the optional parameter host-name to assign a host name to the client.
host apex {
option host-name "apex.example.com";
hardware ethernet 00:A0:78:8E:9E:AA;
fixed-address 192.168.1.4;
}
All subnets that share the same physical network should be declared within a
shared-network declaration as shown below. Parameters within the shared-network, but outside the enclosed subnet declarations, are considered to be global parameters. The name of the shared-network must be a descriptive title for the network, such as using the title 'test-lab' to describe all the subnets in a test lab environment.
shared-network name {
option domain-search "test.redhat.com";
option domain-name-servers ns1.redhat.com, ns2.redhat.com;
option routers 192.168.0.254;
more parameters for EXAMPLE shared-network
subnet 192.168.1.0 netmask 255.255.252.0 {
parameters for subnet
range 192.168.1.1 192.168.1.254;
}
subnet 192.168.2.0 netmask 255.255.252.0 {
parameters for subnet
range 192.168.2.1 192.168.2.254;
}
}
As demonstrated below, the
group declaration is used to apply global parameters to a group of declarations. For example, shared networks, subnets, and hosts can be grouped.
group {
option routers 192.168.1.254;
option subnet-mask 255.255.255.0;
option domain-search "example.com";
option domain-name-servers 192.168.1.1;
option time-offset -18000; # Eastern Standard Time
host apex {
option host-name "apex.example.com";
hardware ethernet 00:A0:78:8E:9E:AA;
fixed-address 192.168.1.4;
}
host raleigh {
option host-name "raleigh.example.com";
hardware ethernet 00:A1:DD:74:C3:F2;
fixed-address 192.168.1.6;
}
}
Imp Notes:
When the DHCP server is started for the first time, it fails unless the dhcpd.leases file exists. Use the command touch /var/lib/dhcpd/dhcpd.leases to create the file if it does not exist.
If the same server is also running BIND as a DNS server, this step is not necessary, as starting the named service automatically checks for a dhcpd.leases file.
To start the DHCP service, use the command
/sbin/service dhcpd start. To stop the DHCP server, use the command /sbin/service dhcpd stop.
By default, the DHCP service does not start at boot time. To configure the daemon to start automatically at boot time, use the command chkconfig dhcpd on
If more than one network interface is attached to the system, but the DHCP server should only be started on one of the interfaces, configure the DHCP server to start only on that device. In
/etc/sysconfig/dhcpd, add the name of the interface to the list of DHCPDARGS:
Configuring a DHCP Client
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.
Make sure that the /etc/sysconfig/network-scripts/ifcfg-eth0 file contains the following lines:
DEVICE=eth0
BOOTPROTO=dhcp
ONBOOT=yes
To use DHCP, set a configuration file for each device.
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.
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.
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