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The TCP/IP Guide  9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)       9  TCP/IP Network Configuration and Management Protocols (BOOTP, DHCP, SNMP and RMON)            9  Host Configuration and TCP/IP Host Configuration Protocols (BOOTP and DHCP)                 9  TCP/IP Dynamic Host Configuration Protocol (DHCP)                      9  DHCP Configuration and Operation

DHCP Overview of Client and Server Responsibilities 1 2 DHCP General Operation and Client Finite State Machine

Client-Specific Parameters and Client Identifiers

The DHCP server will also have certain parameters that are client-specific; the IP address itself is an obvious example, but there are other parameters that may apply to only certain clients on a network. These parameters are stored in some sort of a database, and indexed using a particular client identifier.

The default identifier consists of the client's IP subnet number and its hardware address. Thus, when a server gets a request from a particular subnet it can use the client's hardware address in the request to look up client-specific parameters and return them. The client identifier can be changed if a different identification scheme is desired.

Clients are also responsible for parameter storage, but of course, only their own parameters. Many of these will be obtained from the DHCP server, though some may be supplied in other ways. The specific implementation of the client determines which parameters it considers important and how they are discovered.

Communication of configuration parameters between DHCP clients and servers is accomplished using DHCP options, which replace BOOTP vendor information fields. A number of options were defined when DHCP was first created, and additional new ones have been created over the years. There are today several dozen of these options. Obviously, the ability to have so many different parameters automatically delivered to a client provides a great deal of host configuration flexibility to administrators. DHCP options are described further in the section on DHCP message formats.

DHCP Overview of Client and Server Responsibilities 1 2 DHCP General Operation and Client Finite State Machine