Why Move to DHCP?

A user who is used to BOOTP or RARP might wonder about the differences and advantages of DHCP. The main difference between DHCP and the older protocols is that the older protocols were designed for manual pre-configuration of the host information in a server database, while DHCP allows dynamic allocation of IP addresses and configurations to newly attached hosts.

In addition, DHCP's leasing mechanism permits automatic recovery and reallocation of IP addresses. DHCP is a superset of BOOTP, offering greater flexibility. DHCP builds on BOOTP using the same protocol packet format and mechanisms with certain additions. In this way, DHCP can leverage the BOOTP relay agent functionality already built into routers, and support BOOTP clients directly.

RARP allows a machine to discover its own IP address, which is one of the protocol parameters typically passed to the client system by DHCP or BOOTP. The disadvantage of RARP is that it doesn't support other parameters, and a server providing it can serve only directly attached networks.

DHCP and BOOTP traffic can utilize BOOTP relay agent functionality built into common routers. This means the network administrator does not have to place a BOOTP service on every network segment.

When administrators try to support manually configured IP addresses, they are faced with a number of difficulties:

• There is no way to detect reliably whether an IP address is still in use.

• Any time the network topology changes, such as adding a new network IP address, the administrator has to add new IP addresses manually.

• Hosts configured on one network and then moved to another are not able to communicate without having their configuration manually changed.