> -----Original Message----- > From: ipv6 [mailto:ipv6-bounces@xxxxxxxx] On Behalf Of Job Snijders > NEW: > IPv6 unicast routing is based on prefixes of any valid length up to > 128 [BCP198]. When using [SLAAC], [ILNP], or [NPT66] the Interface ID > of unicast addresses is required to be 64 bits long. In other use > cases different prefix sizes may be required. For example [RFC6164] > standardises 127 bit prefixes on inter-router point-to-point links. > For most use cases, prefix lengths of 64 bits is RECOMMENDED, unless > there are operational reasons not to do so. Sounds about right to me. Another exception that requires /64 would be ULAs. I think that after RFC 2460-bis becomes the standard, this /64 debate will be revisited. Why? To make it super clear that for unicast, in general, /64 are going to be the exception, not the rule (as so much text now suggests). The 64 bit prefix applies to the 2000::/3 address space, and those few exceptions. For example, this is all up in the air still, but we can assume that just as households are being assigned one /64 prefix frequently, so will cars? Each car gets a /64. Does anyone think that cars will only include one IPv6 subnet? Not me. So we will need CIDR. Bert