IAB/IESG Recommendations on IPv6 Address Allocations to Sites (RFC 3177) provides recommendations that for end sites a /48 block should be provided in normal case. A /64 block when it is absolutely sure that only one subnet is needed and /128 for the case that only one device is connected. The requirements for IPv6 in 1993 included the plan that the next IP version should address approximately 2⁴⁰ networks and 2⁵⁰ hosts. Therefore the currently IPv6 address can be loosely splitted in a 64 bit network number (including subneting) and 64 bit host number (including flat EUI-64 host part and randomly self autoconfigured host number) → 2⁴⁰ & 2⁵⁰ goal accomplished.

/48 provides end sites the ability to subnet 2¹⁶ subnet numbers for internal routing infrastructure each with theoretical max. 2⁶⁴ unique hosts. Most enterprises should be happy with this. Very large enterprises should be provided with a /47 or with multiple/48. RFC 3177 constitute a more or less hard default setting and Regional Internet Registries (RIRs) should bear on that. The idea of the IAB/IESG recommendation was that a hard structure will reduce among other things maintainership (e.g. address restructuring, see paragraph 3 for more information).

IPv6 Address Assignment to End Sites started now to obsolete RFC 3177. Thomas Narten et. al. stated that the RIRs originally started with /48 but began to switch to other policies in 2005. Namely APNIC, APNIC and RIPE encourage the assignment of smaller (e.g. /56) blocks to end sites. One concern is that the hard suggestion can lead to a classfull routing where CIDR continues to apply to all bits of the routing prefixes. Another aspect is that RIRs may have other policies which fit better in their model.