Illustrated TCP/IP by Matthew G. Naugle Wiley Computer Publishing, John Wiley & Sons, Inc. ISBN: 0471196568   Pub Date: 11/01/98

Chapter 312
Dynamic Host Configuration Protocol (DHCP)

Which came first, BOOTP or DHCP? Which one does both? Why do you hear about BOOTP every time something is written about DHCP? Since the protocol is based on a broadcast mechanism, why and how do these protocols operate in a routed environment? In fact, why do we need another configuration mechanism when we have DRARP (Dynamic Reverse Address Resolution Protocol) and ICMP (Internet Control Message Protocol)? DRARP addresses the problem of IP address assignment and hosts can use ICMP to find out the subnetmask for a network and to dynamically discover routers, right? And, since we consider a router to sometimes be a host, does DHCP provide configuration information for a router? Or, have you forgotten about those capabilities?

DHCP is gaining considerable attention due to a number of factors: tight address allocation restrictions, which requires efficient assignment or reassignment of IP addresses (IP addresses are in short supply and are handed out very carefully. DHCP offers us the capability of handing them out statistically based on probability. Therefore, we can have many users and not as many IP addresses.).

This chapter explains the DHCP protocol. The DHCP protocol for the purposes of this writing can fully interoperate with BOOTP servers and clients.

Terms used in the DHCP protocol are as follows:

DHCP Client: A host that is requesting configuration information.

DHCP Server: A DHCP hosts that supplies configuration parameters to a requesting host.

BOOTP Relay Agent: The protocol that allows BOOTP and DHCP packets to traverse a router.

Binding: Configuration parameters, including an IP address, that are “bound to” a host.