Once upon a time, TJ <trejrco@tjevans.net> said:

Short answer - no spec for it. ARIN breaks it at /56, as a nod towards maybe a /48 for everyone is a bit much.

On ARIN's site: The following guidelines may be useful (but they are only guidelines): * /64 when it is known that one and only one subnet is needed * /56 for small sites, those expected to need only a few subnets over the next 5 years. * /48 for larger sites For end sites to whom reverse DNS will be delegated, the LIR/ISP should consider making an assignment on a nibble (4-bit) boundary to simplify reverse lookup delegation. So, the guidelines are on 8 bit boundaries, but then right below they also suggest making assignments on 4 bit boundaries (and it is all "only guidelines"). -- Chris Adams <cmadams@hiwaay.net> Systems and Network Administrator - HiWAAY Internet Services I don't speak for anybody but myself - that's enough trouble.