The DHCP server is a central part of the network. We will use ISC's DHCP server, and configure two servers to make a redundant system. The two servers will be able to synchronize the dhcp leases between servers and update the DNS too. They will be running in an active/passive setup.
In this setup we use the following IP-addresses for the primary and secondary:
- 192.168.1.36 primary
- 192.168.1.37 secondary
Once the two servers are configured, you will notice that there is only a small difference between them. The difference is in /etc/dhcp/dhcpd.conf, which includes /etc/dhcp/dhcpd.conf_primary for the DHCP primary and /etc/dhcp/dhcpd.conf_secondary for the DHCP secondary. This is on purpose and will make configuration changes much easier. The config files on the two servers has to be identical. If they are not identical, the DHCP servers will most likely not start. Make a strategy where configuration changes are made on the primary and then copied to the secondary. Just avoid overwriting /etc/dhcp/dhcpd.conf.
The descriptions below apply to both the DHCP primary and the DHCP secondary, meaning that any configuration changes will have to be made on both DHCP servers in identical ways.