R3721-F3210-F3171-HP High-End Firewalls Network Management Configuration Guide-6PW101

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Configuring DHCP relay agent
Introduction to DHCP relay agent
Application environment
Since DHCP clients request IP addresses via broadcast messages, the DHCP server and clients must be
on the same subnet. Therefore, a DHCP server must be available on each subnet, which is not practical.
DHCP relay agent solves the problem. Via a relay agent, DHCP clients communicate with a DHCP server
on another subnet to obtain configuration parameters. Thus, DHCP clients on different subnets can
contact the same DHCP server for ease of centralized management and cost reduction.
Fundamentals
Figure 105 shows a typical application of the DHCP relay agent.
Figure 105 DHCP relay agent application
No matter whether a relay agent exists or not, the DHCP server and client interact with each other in a
similar way (see "DH
CP overview"). The following describes the forwarding process on the DHCP relay
agent.