Le 23/02/2017 à 23:43, David Farmer a écrit :
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 prefer other IID lengths to be RECOMMENDED for implementations, but I can live with OPTIONAL.
But it's already so beautful to say just plen+IID must give 128. Why telling more? Could that be 'over-specifying'?
Alex
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