The 7210 SAS supports DHCPv6 snooping, as described in RFC 6221, Lightweight DHCPv6 Relay Agent. DHCPv6 snooping allows the user to enable the Lightweight DHCPv6 Relay Agent (LDRA) in a VPLS service.
An LDRA allows relay agent information to be inserted by an 7210 SAS access node that performs a link-layer bridging function. An LDRA resides on the same IPv6 link as the client and a DHCPv6 relay agent or DHCPv6 server, and is similar in function to the DHCPv4 snooping function. DHCPv6 snooping allows relay agent information, including the interface ID option, to be inserted by the access node so that it can be used by the DHCPv6 server for client identification. It also allows for insertion of the remote ID option, allowing the DHCPv6 server to know where the client is attached to the network and if the location is trusted.
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From the client to the DHCPv6 server/relay (for example, Discover or Request messages) to insert relay agent information. For these applications, DHCP snooping must be enabled on the SAP (using the config>service>vpls>sap>dhcp6>snoop command) toward the subscriber.
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From the DHCPv6 server or relay (for example, ACK messages) to remove the relay agent information toward the client. For these applications, DHCPv6 snooping must be enabled on both the SAP toward the network (using the config>service>vpls>sap>dhcp6>snoop command), the SDP binding toward the network (using the config>service>vpls>spoke-sdp>snoop or config>service>vpls>mesh-sdp>snoop command), and the SAP toward the subscriber (using the config>service>vpls>sap>dhcp6>snoop command).
Note: On the 7210 SAS, DHCPv6 snooping on SDP bindings is only supported for spoke SDPs and mesh SDPs in TLDP VPLS services.
In the following figure, the 7210 SAS is used as an access aggregation device to aggregate business CPE for enterprise services, Digital Subscriber Line Access Multiplexers (DSLAMs), and Optical Line Terminations (OLTs) for residential broadband services that use Layer 2 VPLS services.
Operators need a mechanism to identify the DHCPv6 messages received on their customer-facing ports so that the appropriate IPv6 address and parameters can be provided by the DHCPv6 server. In a Layer 2 network, this is achieved by using DHCPv6 snooping to insert option-18 and option-37 (relay agent information options) in the DHCPv6 messages received from customer-facing ports before being forwarded toward the DHCPv6 server or relay.