Re: Review of draft-ietf-6man-rfc4291bis-06

[David Farmer <farmer@xxxxxxx>]

On Fri, Jan 13, 2017 at 9:28 PM, Brian E Carpenter <brian.e.carpenter@xxxxxxxxx> wrote:

....

Which is exactly why we have so far only delegated 1/8 of the
IPv6 address space for global unicast allocation, leaving a *lot*
of space for fixing our mistakes. Moving away from /64 as the
recommended subnet size might, or might not, prove to be necessary in
the long term future. That's why the point about routing being
classless is fundamental. I do think we need to be a bit more
precise on this point in 4291bis.

    Brian

Exactly, /64 is the RECOMMENDED subnet size, or a SHOULD from RFC2119, and I'm fine with that, but that's not what the following says.

   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].

It says REQUIRED, that is a MUST from RFC2119, and I believe it to be an Imperative as discussed in section 6 of RFC2119.  

I'm fine with /64, /127 and /128 as the RECOMMENDED subnet sizes, I support that and believe it to be the consensus of the IETF. Maybe even explicitly noting /65 through /126 are NOT RECOMMENDED subnet sizes, and not support by SLACC.  But it is not correct to say the /64 is REQUIRED.

I also believe RFC7608 supports this conclusion.

Thanks.

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