IP networks are divided logically into

subnetwork A subnetwork or subnet is a logical subdivision of an IP network. Updated by RFC 6918. The practice of dividing a network into two or more networks is called subnetting. Computers that belong to the same subnet are addressed with an identical ...

s. Computers in the same subnetwork have the same address prefix. For example, in a typical home network with legacy

Internet Protocol version 4 Internet Protocol version 4 (IPv4) is the fourth version of the Internet Protocol (IP). It is one of the core protocols of standards-based internetworking methods in the Internet and other packet-switched networks. IPv4 was the first version de ...

, the network prefix would be something like 192.168.1.0/24, as expressed in

CIDR notation Classless Inter-Domain Routing (CIDR ) is a method for allocating IP addresses and for IP routing. The Internet Engineering Task Force introduced CIDR in 1993 to replace the previous classful network addressing architecture on the Internet. Its g ...

. With IPv4, commonly home networks use private addresses (defined in ) that are non-routable on the public Internet and use address translation to convert to routable addresses when connecting to hosts outside the local network. Business networks typically had manually provisioned subnetwork prefixes. In

IPv6 Internet Protocol version 6 (IPv6) is the most recent version of the Internet Protocol (IP), the communication protocol, communications protocol that provides an identification and location system for computers on networks and routes traffic ...

global addresses are used end-to-end, so even home networks may need to distribute public, routable IP addresses to hosts. Since it would not be practical to manually provision networks at scale, in

networking,

DHCPv6 The Dynamic Host Configuration Protocol version 6 (DHCPv6) is a network protocol for configuring Internet Protocol version 6 (IPv6) hosts with IP addresses, IP prefixes, default route, local segment MTU, and other configuration data required to ...

prefix delegation is used to assign a

network address prefix A route distinguisher is an address qualifier used only within a single internet service provider's Multiprotocol Label Switching (MPLS) network. It is used to distinguish the distinct virtual private network (VPN) routes of separate customers who ...

and automate configuration and provisioning of the public routable addresses for the network. The way this works for example in case of a home network is that the home router uses DHCPv6 protocol to request a network prefix from the ISP's DHCPv6 server. Once assigned, the ISP routes this network to the customer's home router and the home router starts advertising the new addresses to hosts on the network, either via

SLAAC Internet Protocol version 6 (IPv6) is the most recent version of the Internet Protocol (IP), the communications protocol that provides an identification and location system for computers on networks and routes traffic across the Internet. IPv ...

or using DHCPv6. DHCPv6 Prefix Delegation is supported by most ISPs who provide native IPv6 for consumers on fixed networks. Prefix delegation is generally not supported on

cellular network A cellular network or mobile network is a communication network where the link to and from end nodes is wireless. The network is distributed over land areas called "cells", each served by at least one fixed-location transceiver (typically thre ...

s, for example LTE or 5G. Most cellular networks route a fixed /64 prefix to the subscriber. Personal hotspots may still provide IPv6 access to hosts on the network by using a different technique called Proxy Neighbor Discovery or using the technique described in . One of the reasons why cellular networks may not yet support prefix delegation is that the operators want to use prefixes they can aggregate to a single route. To solve this, defines an optional mechanism and the related DHCPv6 option to allow exclusion of one specific prefix from a delegated prefix set.

See also