Dynamic Host Configuration Protocol (DHCP)

DHCP's purpose is to enable individual computers on an IP network to extract their configurations from a server (the 'DHCP server').

In general, the servers will have no static information about the individual client computers until information is requested. Responses to each client will then be generated dynamically.

The overall purpose of this is to reduce the work necessary to administer a large (often dynamic) IP-based network.

The most significant piece of information distributed in this manner is the IP address.

DHCP is based on BOOTP and maintains some backward compatibility. The main difference is that BOOTP was designed for manual pre-configuration of the host information in a server database, while DHCP allows for dynamic allocation of network addresses and configurations to newly attached hosts. Additionally, DHCP allows for recovery and reallocation of network addresses through a leasing mechanism.

DHCP, like BOOTP, runs over the user-datagram protocol (UDP), using ports 67 and 68, and is defined in RFC-1534 and RFC-2131.

DHCP Configuration

The DHCP daemon (process) is typically provided with the name of a network interface (such as eth0) so that it knows from where to accept broadcast requests.

The DHCP daemon reads information from a configuration file storing the 'public' information for clients. To provide a truly dynamic configuration, we also need to provide a range of IP addresses given to clients.

We can also use DHCP to provide fixed configuration information, based on the Ethernet (MAC) address of the arriving request: