Basic DHCP Configuration

By default, DHCP server configuration does not include any subnets on which DHCP server should lease IP addresses. Therefore, depends on your Linux system you may get the following error message when you attempt to start DHCP with default dhcpd.conf configuration file.

Starting ISC DHCP server: dhcpdcheck syslog for diagnostics. ... failed!

Examining log files such as /var/log/syslog reveals more details:

No subnet declaration for eth0 (some IP address). 

Your server may be connected to multiple network subnets. To start DHCP server, at least one subnet must be defined within the DHCP configuration file /etc/dhcp/dhcpd.conf. 

NOTE: if your server has access to more than one subnet, DHCP requires all subnets to be defined even though there isn't immediate intention to enable DHCP service on that subnet. 

Below is the simplest example of DHCP configuration file:

subnet 10.1.1.0 netmask 255.255.255.0 {
  range 10.1.1.3 10.1.1.254;
}

subnet 192.168.0.0 netmask 255.255.0.0 {
}

This configuration file instructs DHCP server to listen for DHCP client requests on subnet 10.1.1.0 with netmask 255.255.255.0. Furthermore, it will assign IP addresses in range 10.1.1.3 - 10.1.1.254. It also defines an empty definition for subnet with network ID 192.168.0.0. 

Alter the above code with your subnet and insert it into /etc/dhcp/dhcpd.conf. When ready, restart your DHCP server with ( restart command may vary ) :

# service isc-dhcp-server restart