Re: draft-bourbaki-6man-classless-ipv6-00

[Brian E Carpenter <[e-mail]>]

On 11/06/2017 12:00, Manfredi, Albert E wrote:
> -----Original Message-----
> From: ipv6 [mailto:[e-mail]] On Behalf Of Brian E Carpenter
> 
>>> If we remove the 64 bit boundary from 4291, then an update of 2464
>>> will likely result in the removal of any bit boundary there as well.
>>
>> No, for the out-of-the-box reason. I can't see any practical
>> alternative to a fixed length per link type.
> 
> I think there are practical alternatives, so I too would suggest not to state flatly that SLAAC requires fixed length IIDs. Anything that requires RAs to work can make adjustments to its IID, in real time.

It cannot adjust its IID length when assigning itself a link-local address *before*
receiving any RA/PIO messages. But whatever length N of IID it uses to generate its
LL address must match the the prefix length 128-N in a later RA/PIO with A=1.
Otherwise, SLAAC fails.

(see Section 5.5.3 bullet d of RFC4862, as Jinmei-san kindly explained to me.)

So in fact the only thing that works is if the equipment assumes the same IID length
as the router announces (as 128-N). Therefore, N must be predefined.
 
> ULAs and link local would need to create IIDs with no knowledge of the outside world. But not SLAAC.

ULAs have nothing to do with it; SLAAC doesn't care whether a prefix is ULA or
globally reachable. And LL is *not* independent of SLAAC.

Regards
    Brian