R0106-HP MSR Router Series Layer 3 - IP Services Configuration Guide(V7)

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Configuring the DHCP relay agent
Overview
The DHCP relay agent enables clients to get IP addresses from a DHCP server on another subnet. This
feature avoids deploying a DHCP server for each subnet to centralize management and reduce
investment. Figure 21 sho
w
s a typical application of the DHCP relay agent.
Figure 21 DHCP relay agent application
An MCE device serving as the DHCP relay agent can forward DHCP packets between a DHCP server
and clients on either a public network or a private network. For more information about MCE, see MPLS
Configuration Guide.
Operation
The DHCP server and client interact with each other in the same way regardless of whether the relay
agent exists. For the interaction details, see "IP address allocation process." Th
e following only describes
steps related to the DHCP relay agent:
1. After receiving a DHCP-DISCOVER or DHCP-REQUEST broadcast message from a DHCP client,
the DHCP relay agent fills the giaddr field of the message with its IP address and unicasts the
message to the designated DHCP server.
2. Based on the giaddr field, the DHCP server returns an IP address and other configuration
parameters in a response.
3. The relay agent conveys the response to the client.