RE: 6MAN WG Last Call:draft-ietf-6man-ipv6-subnet-model-00.txt

"Hemant Singh (shemant)" <shemant@cisco.com> Thu, 10 July 2008 16:08 UTC

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Subject: RE: 6MAN WG Last Call:draft-ietf-6man-ipv6-subnet-model-00.txt
Date: Thu, 10 Jul 2008 12:09:01 -0400
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From: "Hemant Singh (shemant)" <shemant@cisco.com>
To: <Jinmei_Tatuya@isc.org>, "Suresh Krishnan" <suresh.krishnan@ericsson.com>
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Tatuya,

Since you don't want any new rules added by our draft, we changed bullet
3 related to caching on-link determination. The new bullet text does not
add any normative requirements but clearly says why it is a bad idea to
cache on-link determination.  Also, our draft is about on-link
determination - we are not adding anything related to IPv6 address
caching - we have said repeatedly, save it for another day.

The old text of bullet 3 was:

       On-link determination SHOULD NOT persist across IPv6 interface
       initializations.  Note that section 5.7 of [RFC4862] describes
       the use of stable storage for addresses acquired with stateless
       address autoconfiguration with a note that the Preferred and
       Valid Lifetimes must be retained if this approach is used.
       However no RFC suggests or recommends retaining the on-link
       prefixes.

New text is as follows:

                  If on-link determination persists across IPv6
interface initializations,
                  then lack of IPv6 connectivity can result.  For
example, a host receives
                  an RA from a router with on-link prefix A.  The host
reboots.  During the 
                  reboot, the router sends out prefix A with on-link bit
set and a zero 
                  lifetime to indicate a renumbering.  The host misses
the renumbering.  
                  The host comes online.  Then, the router sends an RA
with no PIO.
                  The host uses cached on-link prefix A and issues NS's
instead of sending
                  traffic to a default router.  The "Observed Incorrect
Implementation Behavior"
                  section below describes how this can result in lack of
IPv6 connectivity. 


Hemant

-----Original Message-----
From: Jinmei_Tatuya@isc.org [mailto:Jinmei_Tatuya@isc.org] 
Sent: Thursday, July 10, 2008 1:15 AM
To: Hemant Singh (shemant)
Cc: Wes Beebee (wbeebee); Thomas Narten; Brian Haberman; Bob Hinden;
ipv6@ietf.org
Subject: Re: 6MAN WG Last Call:draft-ietf-6man-ipv6-subnet-model-00.txt

At Wed, 9 Jul 2008 20:54:04 -0400,
"Hemant Singh (shemant)" <shemant@cisco.com>; wrote:

> Thanks for the reply. Let's see if we can meet common ground with you.
> 
> Our justification for prohibiting on-link caching is only in emails to

> 6man as follows:
> 
>  "What if there are cache-inconsistency problems, prefix renumbering,

> or stale information?  I think it's better just to get rid of  caching

> on-link information in stable storage and get such  information fresh 
> from RA's.  That way, administrators can better  rationalize the 
> behavior of their network from the configured RA's."

And I replied to this justification, saying this itself cannot justify
killing on-link caching while (perhaps implicitly) allowing address
caching.

> Also, when Suresh Krishnan pointed out that he supports bullet 3, he 
> made us explicitly mention in the bullet that it's a new rule. We have

> been clear in the draft where there is a new rule and where it's 
> clarification. Besides this new rule, the rest of the draft is 
> clarification.

Suresh has his right to express his opinion, of course, and so do I.
I would not like this document to set new rules (note, again, that I'm
not objecting to discussing new changes to RFC4861/4862.  I'm simply
objecting to doing that in this document).

---
JINMEI, Tatuya
Internet Systems Consortium, Inc.
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