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Inserting the DHCPv6 Client MAC Address Option (Option 79) In DHCPv6 Packets


The incremental deployment of IPv6 to existing IPv4 networks can result in a dual-stack network environment in which devices act as both DHCPv4 and DHCPv6 clients. In dual-stack scenarios, operators need to be able to associate DHCPv4 and DHCPv6 messages with the same client interface, based on an identifier that is common to the interface.

You can configure a DHCPv6 relay agent to insert the DHCPv6 client MAC address in the packets that the relay sends to a DHCPv6 server. The client MAC address is used to associate DHCPv4 and DHCPv6 messages with the same client interface.

In addition to associating DHCPv4 and DHCPv6 messages from a dual-stack client, having the client MAC address in DHCPv6 packets provides additional information for event debugging and logging related to the client at the relay agent and the server.

When DHCPv6 option 79 is enabled, the DHCPv6 relay agent reads the source MAC address of DHCPv6 Solicit and DHCPv6 Request messages that it receives from a client. The relay agent encapsulates the Solicit and Request messages within a DHCPv6 Relay-Forward message, and inserts the client MAC address as option 79 in the Relay-Forward header before relaying the message to the server.

If the DHCPv6 packet already has a Relay-Forward header, the DHCPv6 relay agent adds the client MAC address if the packet meets the following conditions: the packet has only one Relay-Forward header, the Relay-Forward header was added by an LDRA, and the Relay-Forward header does not already include option 79 information.

You can also configure DHCPv6 option 79 for a lightweight DHCPv6 relay agent (LDRA). An LDRA resides on the same IPv6 link as the DHCPv6 client and relay agent or server and acts as a layer 2 relay agent, without performing the routing function necessary to forward messages to a server or relay agent that resides on a different IPv6 link.

  • To configure DHCPv6 option 79 for a DHCPv6 relay agent (layer 3):
  • To configure DHCPv6 option 79 for an LDRA (layer 2):