On 13/01/2017 12:26, Randy Bush wrote: >>> but i am having a hard time reconciling 2.4.4's insistence on a >>> mandatory 64-bit uuid in all unicast global addresses with 2.4.0, rfc >>> 6141, widespread operational practice, ... clue bat please. >> >> This was discussed extensively in 6MAN and resulted in RFC7421 >> "Analysis of the 64-bit Boundary in IPv6 Addressing”. The text in >> rfc4291bis is: >> >> For all unicast addresses, except those that start with the binary >> value 000, Interface IDs are required to be 64 bits long. >> Background on the 64 bit boundary in IPv6 addresses can be found in >> [RFC7421]. > > thanks for the review that the wg came to this decision in conflict with > operational practice and its own statement in 2.4.0. i did read the > documents. > > since it is incorrect, ietf last call seems to be the time to fix it. > > to be clear, i have no problem with iids being 64-bit. my issue is with > unicast globals being classful in 2.4.4. RFC7421 (which is Informational) calls out RFC 6164 (not 6141!) as an exception. To be precise it says: The de facto length of almost all IPv6 interface identifiers is therefore 64 bits. The only documented exception is in [RFC6164], which standardizes 127-bit prefixes for point-to-point links between routers, among other things, to avoid a loop condition known as the ping-pong problem. I would suggest adding a similar exception statement in 4291bis. Brian