DHCPv6 hardware address

The incremental deployment of IPv6 to existing IPv4 networks results in dual-stacking network environments. Some devices will act as both DHCPv4 and DHCPv6 clients. For these dual-stack situation, here is a need to associate DHCPv4 and DHCPv6 messages with the same client interface. A DHCPv4 server uses the client link-layer address as the customer identifier and a key for lookup in the client database. The DHCPv6 Relay-Forward message carries the client link-layer address to the DHCPv6 server allowing the association of both DHCPv4 and DHCPv6 messages with the same client interface.

As defined in RFC-6939, DHCPv6 relay agents receiving solicit and request messages that originate from DHCPv6 clients include the link-layer source address of the received DHCPv6 message. This is accomplished in the Client Link-Layer Address option within DHCPv6 Relay-Forward messages. The Client Link-Layer Address enables the server to recognize and service specific clients. DHCPv6 relay agent behavior (as set by the configuration) decides whether the Client Link-Layer Address option is included for each client.

DHCPv6 relays agents include Option–79 for all message types when enabled. The message types are: solicit, request, confirm, decline, renew, rebind, release and information-request. DHCPv6 provides additional information for event debugging and logging related to the client at the server.


All cascading relay-agents simply encapsulate the message received and relay-forward to the server. The service function does not receive any message-types directly from the client even when the feature is enabled.