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

2017-01-13 13:45:10
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: fgont(_at_)si6networks(_dot_)com
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