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It can also be expressed as ::1
The design of the IPv6 address space differs significantly from IPv4. The primary reason for subnetting in IPv4 is to improve efficiency in the utilization of the relatively small address space available, particularly to enterprises. No such limitations exist in IPv6, as the address space available even to end-users is large.
An IPv6 subnet always has 64 bits in its host portion. It therefore has a /64 routing prefix (the 64 most-significant bits). Although it is technically possible to use smaller subnets, they are impractical for local area networks because stateless address autoconfiguration of network interfaces (RFC 4862) requires a /64 address. IPv6 does not implement special address formats for broadcast traffic or network numbers, and thus all addresses in a subnet are valid host addresses.
The recommended allocation for an IPv6 customer site is an address space of 80 address bits (prefix /48), but it may be as small as 72 bits (/56 allocation) for a residential customer network. This provides 65,536 subnets for a site, or at least a minimum of 256 subnets for a residential network. Subnetting in IPv6 is used to route traffic between the global allocation spaces and within customer network between subnets and the larger Internet. Subnetting in IPv6 is also based on the concepts of Classless Inter-Domain Routing and the standard CIDR notation is used with IPv6 addresses.