DHCPv6 Relay Agent Implementation

Figure 1 shows the working process of a DHCPv6 relay agent. A DHCPv6 client sends packets to a DHCPv6 server through a DHCPv6 relay agent to obtain IPv6 addresses, prefixes, and other network configuration parameters, such as IPv6 addresses of DNS servers.

Figure 1 DHCPv6 relay agent implementation

The working process of a DHCPv6 relay agent is as follows:

1. A DHCPv6 client sends DHCPv6 Request packets with the destination multicast address FF02::1:2 to all DHCPv6 servers and DHCPv6 relay agents.
2. A DHCPv6 relay agent processes packets in the following two ways:

   • If a DHCPv6 relay agent and a DHCPv6 client are located on the same link, that is, the DHCPv6 relay agent is the first-hop relay agent of the DHCPv6 client, the DHCPv6 relay agent is the IPv6 gateway of the DHCPv6 client. After receiving a packet from the DHCPv6 client, the DHCPv6 relay agent encapsulates the packet in the Relay Message option of a Relay-Forward packet. Then the DHCPv6 relay agent sends the Relay-forward packet to a DHCPv6 server or the next hop relay agent.

   • If the DHCPv6 relay agent and DHCPv6 client are on different links, the DHCPv6 relay agent receives Relay-Forward packets sent from other relay agents. The DHCPv6 relay agent constructs a new Relay-Forward packet and sends the packet to the DHCPv6 server or the next hop relay agent.
3. The DHCPv6 server parses the request of the DHCPv6 client in the Relay-Forward packet and selects IPv6 addresses and other network configuration parameters to construct a reply packet. Then the DHCPv6 server encapsulates the reply packet in the Relay Message option in a Relay-Reply packet and sends the Relay-reply packet to the DHCPv6 relay agent.
4. The DHCPv6 relay agent parses the reply packet of the DHCPv6 server in the Relay-Reply packet and forwards the reply packet to the DHCPv6 client. If the DHCPv6 client receives reply packets from multiple DHCPv6 servers, the DHCPv6 client selects the DHCPv6 server with the highest priority, and obtains the IPv6 address and other network configuration parameters from the DHCPv6 server.