For those that don't follow the ARIN Public Policy Mailing List, the following is excerpted from a post by Thomas Narten in response to the announcement that the
<acronym title="Internet Engineering Steering Group">IESG
</acronym> has approved a new document to replace the existing RFC 3177 (IPv6 Address Assignment to End Sites).
> The IESG has approved the following document:
> - 'IPv6 Address Assignment to End Sites'
> (draft-ietf-v6ops-3177bis-end-sites-01.txt) as a BCP
Quoting from the Introduction:
This document obsoletes RFC 3177, updating its recommendations in the following ways:
1) It is no longer recommended that /128s be given out. While there may be some cases where assigning only a single address may be justified, a site by definition implies multiple subnets and multiple devices.
2) RFC 3177 specifically recommended using prefix lengths of /48, /64 and /128. Specifying a small number of fixed boundaries has raised concerns that implementations and operational practices might become "hard-coded" to recognize only those fixed boundaries (i.e., a return to "classful addressing"). The actual intention has always been that there be no hard-coded boundaries within addresses, and that CIDR continues to apply to all bits of the routing prefixes.
3) This document moves away from the previous recommendation that a single default assignment size (e.g., a /48) makes sense for all end sites in the general case. End sites come in different shapes and sizes, and a one-size-fits-all approach is not necessary or appropriate.
This document does, however, reaffirm an important assumption behind RFC 3177:
A key principle for address management is that end sites always be able to obtain a reasonable amount of address space for their actual and planned usage, and over time ranges specified in years rather than just months. In practice, that means at least one /64, and in most cases significantly more. One particular situation that must be avoided is having an end site feel compelled to use IPv6-to-IPv6 Network Address Translation or other burdensome address conservation techniques because it could not get sufficient address space.