4000 Router Series Layer 3 - IP Services Configuration Guide

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 20 sho

ws a typical application of the DHCP relay agent.

Figure 20 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.

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 "Dynamic 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.