H3C Technologies H3C S5560 Series Switches - Manual (Page 69)

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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 shows a typical application of the DHCP relay agent.
Figure 21 DHCP relay agent application
An MCE device acting 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.
NOTE:
The term "interface" in this section collectively refers to Layer 3 interfaces, including VLAN interfaces and
Layer 3 Ethernet interfaces. You can set an Ethernet port as a Layer 3 interface by using the port link-mode
route command (see Layer 2—LAN Switching 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 ." The 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.