DHCPv6 Relay Agent Include Options
In some network environments, it is useful for the relay agent to add information to the DHCPv6 message before relaying it. The information that the relay agent carries can also be used by the DHCP server to make decisions about the addresses, delegated prefixes, and configuration parameters that the client should receive. The DHCPv6 relay-forward message contains relay agent parameters that identify the client-facing interface on which the reply messages can be forwarded. You can use either one or all of the parameters as client identifiers.
The following options can be included in the relay-forward messages:
The relay agent may send the interface-ID option (18) to identify the interface on which a client message was received. If the relay agent cannot use the address in the link-address field to identify the interface through which the response to the client will be relayed, the relay agent must include an interface-ID option in the relay-forward message. If the relay agent receives a relay-reply message with an interface-ID option, the relay agent relays the message to the client through the interface identified by the option. The server must also copy the interface-ID option from the relay-forward message into the relay-reply message the server sends to the relay agent in response to the relay-forward message.
The remote-ID option (37) may be added by the DHCP relay agent that terminates switched or permanent circuits and uses a mechanism to identify the remote host end of the circuit. The remote ID must be unique. A DHCPv6 relay agent can be configured to include a remote-ID option in the relay-forward DHCPv6 messages.
The client link layer (MAC) address option (79) can be used along with other identifiers to associate DHCPv4 and DHCPv6 messages from a dual-stack client, and is useful in environments where operators using an existing DHCPv4 system with the client link layer address as the customer identifier need to correlate DHCPv6 assignments using the same identifier.