Prefix delegation

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In IPv6 networking, prefix delegation is used to assign a network address prefix to a user site, configuring the user's router with the prefix to be used for each LAN. This is one of the methods for delegating IPv6 address prefixes to an IPv6 subscriber's network (or "site"). It is described by RFC 3769.

With the advent of IPv6 protocol, there is a need for a delegation mechanism which will automate the process of configuring networking equipment with appropriate prefixes at the customer's site.

Though IPv6 enables simple and automatic host configuration it does not provide specification to automatically delegate a prefix to routers. DHCPv6 is used for the automatic configuration of IPv6 nodes. In the DHCPv6 protocol DHCPv6 servers send the network configuration parameters to IPv6 nodes.

The prefix delegation mechanism is intended for simple delegation of prefixes from a delegating router to requesting routers. It is appropriate for situations in which the delegating router does not have 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 customer premise equipment (CPE) acting as a router between the subscriber's internal network and the service provider's core network.

The mechanism for automated delegation of IPv6 prefixes using the Dynamic Host Configuration Protocol for IPv6 (DHCPv6) is defined in RFC 3633.

RFC 6603 defines an optional mechanism and the related DHCPv6 option to allow exclusion of one specific prefix from a delegated prefix set when using DHCPv6-based prefix delegation. The prefix exclusion mechanism is targeted at deployments where DHCPv6-based prefix delegation is used, but a single aggregated route/prefix has to represent one customer, instead of using one prefix for the link between the delegating router and the requesting router and another prefix for the customer network.

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