DHCP is based on the Bootstrap Protocol (BOOTP) and maintains some backward compatibility. BOOTP was designed for manual configuration of the host information in a server database. Novell has extended support for BOOTP to provide Dynamic BOOTP support. A pool of addresses can be set up for BOOTP address assignment so that each BOOTP address does not have to be configured separately.
From the clients' point of view, DHCP is an extension of BOOTP, enabling existing BOOTP clients to interoperate with DHCP servers without requiring any change to the clients' initialization software. Some new, additional options optimize DHCP client-server interaction.
There are two primary differences between DHCP and BOOTP. DHCP defines methods through which clients receive IP addresses for a specified period of time, enabling serial reassignment of addresses to different clients. There is no concept of a lease time in BOOTP; address assignments (even in Dynamic BOOTP) are permanent. Additionally, DHCP provides a method for a client to acquire all the IP configuration parameters it requires to operate.
If multiple servers service a single subnet, only one server, the principal server, can be designated as an automatic BOOTP server.
Another difference between the two protocols is a change in terminology to clarify the meaning of the vendor extension field in BOOTP messages. With DHCP, this field is called the option field.