3Com S7902E, Configuration Manual

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DHCP Relay Agent Configuration
When configuring the DHCP relay agent, go to these sections for information you are interested in:
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Introduction to DHCP Relay Agent
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DHCP Relay Agent Configuration Task List
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Configuring the DHCP Relay Agent
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Displaying and Maintaining DHCP Relay Agent Configuration
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DHCP Relay Agent Configuration Examples
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Troubleshooting DHCP Relay Agent Configuration
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 3-1 shows a typical application of the DHCP relay agent.
Figure 3-1 DHCP relay agent application
IP network
DHCP server
DHCP relay agent
DHCP client DHCP client
DHCP client DHCP client
No matter whether a relay agent exists or not, the DHCP server and client interact with each other in a
similar way (see section Dynamic IP Address Allocation Process ). The following describes the
forwarding process on the DHCP relay agent.