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

[Fernando Gont <[e-mail]>]

On 01/12/2017 10:55 PM, Brian E Carpenter wrote:
> On 13/01/2017 13:50, Randy Bush wrote:
>>> 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.
>>
>> and then next year we will go through another draft and have another
>> exception.  just get rid of classful addressing.  we went through this
>> in the '90s.
> 
> The problem is (and why we wrote 7421) is that stuff breaks with subnet
> prefixes longer than 64, *except* for the point-to-point case covered
> by 6164. Yes, I see the problem in enshrining this but I think we face
> signifcant issues if we do otherwise.
> 
> What we could conceivably say is that /64 is mandatory except for
> links where SLAAC will never be used. (SLAAC itself is designed
> to work with any reasonable length of IID, but again in practice it
> only works with /64, because we need mix-and-match capability. So
> although IID length is a parameter in the SLAAC design, it's a
> parameter whose value needs to be fixed globally.)

Well, yes and no. With the traditional slaac (embed the mac address) it
only works with 64-bit IIDs. With something like RFC7217 (grab as many
bits as needed to for an IID), it could work.

Thanks,
-- 
Fernando Gont
SI6 Networks
e-mail: [e-mail]
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