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Table Of Contents  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

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DHCP Overview of Client and Server Responsibilities
(Page 2 of 2)

DHCP Client Responsibilities

A DHCP client is any device that sends DHCP requests to a server to obtain an IP address or other configuration information. Due to the advantages of DHCP, most host computers on TCP/IP internetworks today include DHCP client software, making them potential DHCP clients if their administrator chooses to enable the function. The main responsibilities of a DHCP client are:

  • Configuration Initiation: The client takes the active role by initiating the communication exchange that results in it being given an IP address and other parameters. The server, in contrast, is passive and will not really do anything for the client until the client makes contact.

  • Configuration Parameter Management: The client maintains parameters that pertain to its configuration, some or all of which may be obtained from a DHCP server.

  • Lease Management: Assuming its address is dynamically allocated, the client keeps track of the status of its own lease. It is responsible for renewing the lease at the appropriate time, rebinding if renewal is not possible, and terminating the lease early if the address is no longer needed.

  • Message Retransmission: Since DHCP uses the unreliable User Datagram Protocol for messaging, clients are responsible for detecting message loss and retransmitting requests if need be.
DHCP Device Roles and Interaction

The DHCP server and client obviously play complementary roles. The server maintains configuration parameters for all clients; each client maintains its own parameters, as discussed in the next topic. IP address assignment and lease creation, renewal, rebinding and termination are accomplished through specific exchanges using a set of eight DHCP message types, which we will see later in this section. To accomplish this messaging, special rules are followed to generate, address and transport messages, which are explained in a topic in the section on DHCP messaging.

Like BOOTP, DHCP also supports a third type of device, the relay agent. Relay agents are neither clients nor servers, but rather intermediaries that facilitate cross-network communication between servers and clients. They are described in more detail in the section on DHCP implementation and features (where you can also find more of the implementation details of servers and clients.)

Key Concept: DHCP servers are devices programmed to provide DHCP services to clients. They manage address information and other parameters and respond to client configuration requests. DHCP clients are TCP/IP devices that have been set to use DHCP to determine their configuration. They send requests and read responses, and are responsible for managing their own leases, including renewing or rebinding a lease when necessary.

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Version 3.0 - Version Date: September 20, 2005

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