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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 22 sho
ws a typical application of the DHCP relay agent.
Figure 22 DHCP relay agent application
An MCE device serving as the DHCP relay agent can forward DHCP packets not only between a DHCP
server 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.
NOTE:
The term "interface" in this section collectively refers to Layer 3 interfaces, includin
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." T
he 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.
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