On 22 February 2017 at 06:21, Karsten Thomann <karsten_thomann@xxxxxxxxx> wrote: > Am Dienstag, 21. Februar 2017, 18:27:39 schrieb Job Snijders: >> On Tue, Feb 21, 2017 at 09:49:32AM +0900, Lorenzo Colitti wrote: >> > On Tue, Feb 21, 2017 at 8:57 AM, Job Snijders <job@xxxxxxx> wrote: <snip> >> >> ------- >> >> OLD: >> IPv6 unicast routing is based on prefixes of any valid length up to >> 128 [BCP198]. For example, [RFC6164] standardises 127 bit prefixes >> on inter-router point-to-point links. However, the Interface ID of >> all unicast addresses, except those that start with the binary value >> 000, is required to be 64 bits long. The rationale for the 64 bit >> boundary in IPv6 addresses can be found in [RFC7421] >> >> 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. > > Satisfies my desired outcome of the text, but I would like to modify it: > 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. An exception is for > example [RFC6164] which standardises 127 bit prefixes on point-to-point > links. The RECOMMENDED prefix length is 64 bit, It has to be stronger than a RECOMMENDED, because that implies it is an arbitrary choice that won't have any protocol operational and privacy or security impacts. That is not the case. Have you and Job read, "Analysis of the 64-bit Boundary in IPv6 Addressing https://tools.ietf.org/html/rfc7421 ? (It has been referenced at some point in a version of this text proposed I think.) Regards, Mark.