IPv6

The IPv6 address space is 128-bits (2128) in size, containing  340,282,366,920,938,463,463,374,607,431,768,211,456 IPv6 addresses.

IPv6 is similar to IPv4, but it is structured so that all LANs have 64 bits  of network prefix as opposed to the variable length of network prefix¹ that IPv4 networks have. All IPv6  networks have space for 18,446,744,073,709,551,616 IPv6 addresses.

Currently, most ISPs assign /48 network prefixes to subscribers sites (the  End Users networks). Because all IPv6 netwoks have /64 prefixes, a /48 network  prefix allows 65,536 LANs in an End User site

The current minimum IPv6 allocation made by the RIPE NCC is a /32 network  prefix. If the LIR only made /48 assignments from
this /32 network prefix,

they  would be able to make 65,536 /48 assignments. If they decided to only assign /56  network prefixes they would have 24 bits
available to them, and so could make  16,777,216 /56 assignments.

For example, if a /24 IPv6 allocation is made to an LIR, it would be able to  make 16,777,216 /48 assignments or 4,294,967,296 /56
assignments.

To give some perspective, it is worth noting that there are 4,294,967,296  IPv4 addresses in total, significantly less than the
number of IPv6  addresses.

IPv6 Relative Network Sizes

/128	1 IPv6 address	A network interface
/64	1 IPv6 subnet	18,446,744,073,709,551,616 IPv6 addresses
/56	256 LAN segments	Popular prefix size for one subscriber site
/48	65,536 LAN segments	Popular prefix size for one subscriber site
/32	65,536 /48 subscriber sites	Minimum IPv6 allocation
/24	16,777,216 subscriber sites	256 times larger than the minimum IPv6 allocation

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