Reference Guide

Dynamic Host Configuration Protocol | 307
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Dynamic Host Configuration Protocol
Dynamic Host Configuration Protocol is available on platforms: c e s Z
This chapter contains the following sections:
• Protocol Overview
• Implementation Information
• Configuration Tasks
• Configure the System to be a DHCP Server
• Configure the System to be a Relay Agent
• Configure Secure DHCP
Protocol Overview
Dynamic Host Configuration Protocol (DHCP) is an application layer protocol that dynamically assigns IP
addresses and other configuration parameters to network devices based on configuration policies
determined by network administrators. DHCP:
• relieves network administrators of manually configuring hosts, which is a can be a tedious and
error-prone process when hosts often join, leave, and change locations on the network.
• reclaims IP addresses that are no longer in use to prevent address exhaustion.
DHCP is based a client-server model. A host discovers the DHCP server and requests an IP address, and
the server either leases or permanently assigns one. There are three types of devices that are involved in
DHCP negotiation:
• DHCP Server—a network device offering configuration parameters to the client.
• DHCP Client—a network device requesting configuration parameters from the server.
• Relay agent—an intermediary network device that passes DHCP messages between the client and
server when the server is not on the same subnet as the host.
DHCP Packet Format and Options
DHCP uses UDP as its transport protocol. The server listens on port 67 and transmits to port 68; the client
listens on port 68 and transmits to port 67. The configuration parameters are carried as options in the
DHCP packet in Type, Length, Value (TLV) format; many options are specified in RFC 2132. To limit the
number parameters that servers must provide, hosts specify the parameters that they require, and the server