DHCPv6 Relay Agent Prefix Delegation

DHCPv6 Prefix Delegation options provide a mechanism for automated delegation of IPv6 prefixes using DHCP. This mechanism is intended for delegating a long-lived prefix from a delegating router to a requesting router, across an administrative boundary, where the delegating router does not have/require knowledge about the topology of the networks to which the requesting router is attached, and the delegating router does not require other information aside from the identity of the requesting router to choose a prefix for delegation.

For example, these options would be used by a service provider to assign a prefix to a Customer Premise Equipment (CPE) device acting as a router between the subscriber's internal network and the service provider's core network.

This prefix delegation mechanism is appropriate for use by an ISP to delegate a prefix to a subscriber, where the delegated prefix would possibly be sub-netted and assigned to the links within the subscriber's network.

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Prefix Delgation Example
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The prefix delegation process begins when the requesting router requests configuration information through DHCP. When the delegating router receives the request, it selects and returns an available prefix or prefixes for delegation to the requesting router.

The requesting router now acts as a DHCP server for the subscriber network. It subnets the delegated prefix and assigns the longer prefixes to links in the subscriber's network. In a typical scenario based on the network shown in Figure 1, the requesting router subnets a single delegated /48 prefix into /64 prefixes and assigns one /64 prefix to each of the links in the subscriber network.

Prefix delegation with DHCP is independent of address assignment with DHCP. A requesting router can use DHCP for just prefix delegation or for prefix delegation along with address assignment and other configuration information.