Using Lightweight DHCPv6 Relay Agent (LDRA)

In Layer 2 networks that have many nodes on a single link, a DHCP server would normally be unaware of how a DHCP client is attached to the network. In a DHCPv6 deployment, you can use a Lightweight DHCPv6 Relay Agent (LDRA) to add relay agent information to a DHCPv6 message to identify the client-facing interface of the access node that received the message. The server can use this information to assign IP addresses, prefixes, and other configuration parameters for the client.

DHCPv6 relay agents are typically used to forward DHCPv6 messages between clients and servers or other relay agents when they are not on the same IPv6 link node. The relay agent can add information to the messages before relaying them. When the client and server reside on the same IPv6 link, LDRA enables a switching device to perform the function of intercepting DHCPv6 messages and inserting relay agent information that can be used for client identification. The LDRA acts as a relay agent, but without performing the routing function necessary to forward messages to a server or relay agent that resides on a different IPv6 link.

When the LDRA receives a DHCPv6 Solicit message from a client, it encapsulates that message within a DHCPv6 Relay-Forward message, which it then forwards to the server or another relay agent. Before it forwards the Relay-Forward message, the LDRA can also insert relay information by using one or more of the following options:

• option-16 (Vendor ID)—Option 16 provides the server with information about the vendor that manufactured the hardware on which the DHCPv6 client is running. Option 16 is the DHCPv6 equivalent of the vendor-id suboption of DHCP option 82.

• option-18 (Interface ID)—A unique identifier for the interface on which the client DHCPv6 packet is received. Suboptions can be configured to include a prefix with the interface ID or to change the type of information used to identify the interface. Option 18 is the DHCPv6 equivalent of the circuit-id suboption of DHCP option 82.

• option-37 (Remote ID)—A unique identifier for the remote host. Suboptions can be configured to include a prefix with the remote ID or to change the interface portion of the ID. Option 37 is the DHCPv6 equivalent of the remote-id suboption of DHCP option 82.