55Configuring the DHCP relay agentOverviewThe DHCP relay agent enables clients to get IP addresses from a DHCP server on another subnet. Thisfeature avoids deploying a DHCP server for each subnet to centralize management and reduceinvestment. Figure 20 shows a typical application of the DHCP relay agent.Figure 20 DHCP relay agent applicationAn MCE device serving as the DHCP relay agent can forward DHCP packets not only between a DHCPserver and clients on a public network, but also between a DHCP server and clients on a private network.For more information about MCE, see MPLS Configuration Guide.OperationThe DHCP server and client interact with each other in the same way regardless of whether the relayagent exists. For the interaction details, see "Dynamic IP address allocation process." The following onlydescribes 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 themessage to the designated DHCP server.2. Based on the giaddr field, the DHCP server returns an IP address and other configurationparameters in a response.3. The relay agent conveys the response to the client.
