This topic describes how the DHCP relay agent notification for prefix delegation feature enables the Cisco 8000 Series Router, working as a DHCPv6 relay agent, to find prefix delegation options and manage subscriber routes.
DHCP relay agent notification for prefix delegation allows the router working as a DHCPv6 relay agent to
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find prefix delegation options,
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review the contents of a DHCP RELAY-REPLY packet that is sent to the client,
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extract information about the delegated prefix, and
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insert an IPv4 or IPv6 subscriber route that matches the prefix delegation information onto the relay agent.
A relay agent forwards future packets that are destined to that prefix based on the information contained in the prefix delegation. The relay agent automatically does the subscriber route management.
The IPv4 or IPv6 routes are added when the relay agent relays a RELAY-REPLY packet. The IPv4 or IPv6 routes are deleted when the prefix delegation lease time expires or the relay agent receives a release message. An IPv4 or IPv6 subscriber route in the routing table of the relay agent is updated when the prefix delegation lease time is extended.
This feature leaves an IPv4 or IPv6 route on the routing table of the relay agent. This registered IPv4 or IPv6 address allows a Unicast Reverse Path Forwarding (uRPF) to work by allowing the router to do the reverse lookup. The reverse lookup enables you to confirm that the IPv4 or IPv6 address on the relay agent is not malformed or spoofed. The IPv6 route in the routing table of the relay agent can be redistributed to other routing protocols to advertise the subnets to other nodes. When the client sends a DHCP_DECLINE message, the routes are removed.