4000 Router Series Layer 3 - IP Services Configuration Guide

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Configuring the DHCPv6 relay agent

A DHCPv6 client usually uses a multicast address to contact the DHCPv6 server on the local link to obtain

an IPv6 address and other configuration parameters. As shown in Figure 86, if the D

HCPv6 server

resides on another subnet, the DHCPv6 clients need a DHCPv6 relay agent to contact the server. The

relay agent feature avoids deploying a DHCP server on each subnet.

Figure 86 Typical DHCPv6 relay agent application

As shown in Figure 87, a DHCPv6 client obtains an IPv6 address and other network configuration

parameters from a DHCPv6 server through a DHCPv6 relay agent in the following steps (rapid

assignment involving two messages):

• The DHCPv6 client sends a Solicit message containing the Rapid Commit option to the multicast

address FF02::1:2 of all the DHCPv6 servers and relay agents.

• After receiving the Solicit message, the DHCPv6 relay agent encapsulates the message into the

Relay Message option of a Relay-forward message, and sends the message to the DHCPv6 server.

• After obtaining the Solicit message from the Relay-forward message, the DHCPv6 server selects an

IPv6 address and other required parameters, adds them to a reply that is encapsulated within the

Relay Message option of a Relay-reply message, and sends the Relay-reply message to the DHCPv6

relay agent.

• The DHCPv6 relay agent obtains the reply from the Relay-reply message and sends the reply to the

DHCPv6 client.

• The DHCPv6 client uses the IPv6 address and other network parameters assigned by the DHCPv6

server to complete network configuration.

IPv6 network

DHCPv6 server

DHCPv6 relay agent

DHCPv6 client DHCPv6 client

DHCPv6 clientDHCPv6 client