This chapter provides an introduction to the Dynamic Host Configuration Protocol (DHCP). As you will see, DHCP shares many traits with BOOTP. However, they are two separate protocols and as such operate in different ways. I will also detail the DHCP conversation that takes place between a DHCP client and DHCP server. Finally I will cover DHCP relay agents, which allow DHCP to operate in a subnetted environment by relaying requests between the client and server, and how relay agents operate.
As shown in the previous chapters, RARP and BOOTP made inroads towards creating a way to dynamically configure a host on a TCP/IP-based network. RARP provided a means of obtaining an IP address; however, it could only function on a single subnet and did not provide any other configuration information, such as the subnet mask and default gateway. BOOTP alleviated some of the problems of RARP, but an administrator still had to maintain static configuration files on the BOOTP server. Also, BOOTP clients could not renew their configurations until the system was restarted, thus triggering the BOOTP process.
DHCP, defined in RFC2131 and RFC2132, was developed to alleviate many of these shortcomings and to accomplish the following:
DHCP allows administrators to control configuration parameters on their network.
Clients using DHCP can be dynamically configured. This allows additions and changes to networks without the need to visit each individual host or workstation. ...