On 02/23/2017 07:43 PM, David Farmer wrote: > > > On Wed, Feb 22, 2017 at 10:16 PM, Lorenzo Colitti <lorenzo@xxxxxxxxxx > <mailto:lorenzo@xxxxxxxxxx>> wrote: > > Help he understand, then. There is widely-deployed code that assumes > that the interface ID is 64 and does not work on anything other than > 64 bit prefix lengths. Currently that code is correct on all unicast > space. If you change RFC 4291, won't that code be incorrect? > > > OK, what if we said something like this; > > IPv6 unicast routing is based on prefixes of any valid length up to > 128 [BCP198]. However, all implementations of IPv6 are REQUIRED to > support an IID length of 64 bits, other IID lengths are OPTIONAL. > Subnet prefixes of /64 are RECOMMENDED for general purpose use, > subnet prefixes of /127 are RECOMMENDED for point-to-point router > links [RFC6164], other subnet prefix lengths are NOT RECOMMENDED, > as their use could be incompatible with some implementations of IPv6. > The rationale for the 64 bit boundary in IPv6 addresses can be found > in [RFC7421]. I'd remove a few sentences here, as in: IPv6 unicast routing is based on prefixes of any valid length up to 128 [BCP198]. Subnet prefixes of /64 are RECOMMENDED for general purpose use, subnet prefixes of /127 are RECOMMENDED for point- to-point router links [RFC6164]. The rationale for the 64 bit boundary in IPv6 addresses can be found in [RFC7421]. Thanks, -- Fernando Gont SI6 Networks e-mail: fgont@xxxxxxxxxxxxxxx PGP Fingerprint: 6666 31C6 D484 63B2 8FB1 E3C4 AE25 0D55 1D4E 7492