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

"Wes Beebee (wbeebee)" <wbeebee@cisco.com> Fri, 25 July 2008 13:44 UTC

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Subject: RE: 6MAN WG Last Call:draft-ietf-6man-ipv6-subnet-model-00.txt
Date: Fri, 25 Jul 2008 09:45:03 -0400
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From: "Wes Beebee (wbeebee)" <wbeebee@cisco.com>
To: "Hemant Singh (shemant)" <shemant@cisco.com>, <Jinmei_Tatuya@isc.org>
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Sounds good to me...  We mainly want to say blind caching of on-link
determination is bad,
but verifying that it's still good (as DNA does) will fix the problem.

I'm happy with adopting Tatuya's new text.  After all, an administrator
may set the lifetime of 
a prefix to 0xFFFFFFFF (infinity) - which means that the renumbering
state would have to go
on forever in order to deprecate the prefix and be sure that every host
will get the information.

At least if hosts verify the information is still good, then the
administrator could end the renumbering
in a reasonable time frame and hopefully the affected hosts will be able
to recover.

Also, my example was one person going on vacation - but if Comcast ends
up doing this, they 
could end up having to deal with any of 10 million+ people turning on
and off their computers...

I appreciate that we were able to reach consensus on this and close on
this issue.

Thanks,
- Wes

> _____________________________________________ 
> From: 	Hemant Singh (shemant)  
> Sent:	Friday, July 18, 2008 11:20 AM
> To:	'Jinmei_Tatuya@isc.org';; Wes Beebee (wbeebee)
> Cc:	Suresh Krishnan; Thomas Narten; Brian Haberman; Bob Hinden;
> ipv6@ietf.org
> Subject:	RE: 6MAN WG Last
> Call:draft-ietf-6man-ipv6-subnet-model-00.txt
> 
> Tatuya,
> 
> Thanks for all your email. Please see in line between <hs> and </hs>.
> 
> -----Original Message-----
> From: Jinmei_Tatuya@isc.org [mailto:Jinmei_Tatuya@isc.org] 
> Sent: Thursday, July 17, 2008 9:44 PM
> To: Wes Beebee (wbeebee)
> Cc: Hemant Singh (shemant); Suresh Krishnan; Thomas Narten; Brian
> Haberman; Bob Hinden; ipv6@ietf.org
> Subject: Re: 6MAN WG Last
> Call:draft-ietf-6man-ipv6-subnet-model-00.txt
> 
> At Thu, 10 Jul 2008 16:21:35 -0400,
> "Wes Beebee (wbeebee)" <wbeebee@cisco.com>; wrote:
> 
> > The problem is that one problem is FAR more likely to happen than
> the other.
> > 
> > I shutdown my machine every night and power it on again in the
> morning 
> > when I come to work.  Therefore, every night of every workday I 
> > experience the type of outage described in our draft.
> > Furthermore, I occasionally go on vacations too - so the outage may
> Tatuya
> > last more than a day.
> > 
> > What this means for an administrator is that he has to predict, in 
> > advance, how long I may be on vacation so that the RA deprecating
> the 
> > old prefix can last long enough.  That puts an unreasonable 
> > expectation on the network administrator.  Furthermore, I don't want
> 
> > to have to get permission from my network administrator in order to
> go 
> > on vacation.
> 
> You're using inappropriate examples to justify the proposed text:
> 
> <hs>
> Agreed. However, Wes did make a point that these are problems FAR more
> likely to happen and also gave examples of timeframes that are much
> longer than the reload time for a host. Like weeks of vacation or 6-8
> hours every night. 
> </hs>
> 
>    Using cached on-link determination information without first
>    verifying that the information is still valid after IPv6 interface
>    re-initialization may lead to lack of IPv6 network connectivity.
> 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.
> 
> This reads to me that the outage is a pretty short time (i.e., while
> the host is rebooting), while assuming the administrator stops
> advertising the 0-lifetime RAs so quickly.  That's why I said "what's
> wrong in this scenario is that the router doesn't keep advertising
> 0-lifetime-prefixes sufficiently long".
> 
> Even if in the vacation case, the administrator shouldn't stop
> advertising 0-lifetime RAs as long as some hosts may keep an old
> address or prefix.  Note that they don't have to predict anything
> about the users' vacation plan to do so: the necessary period can be
> calculated from the previously advertised lifetime and the time when
> the renumbering procedure starts.
> 
> Having said that, I see your point if we are mainly considering a case
> of reconnecting after a long term absence such as a vacation.  Even
> though the administrator should keep advertising 0-lifetime RAs to
> avoid confusion, it should also be advisable for the host to purge the
> old information (or at least confirm whether it's still valid).
> 
> <hs>
> We just don't want to completely rely on an admin of the router
> network to do the right thing and not say, fat-finger any
> configuration. Soon as any admin mis-configuration is done, we can get
> into the problem of Section 3 and data forwarding stops. The host
> should be defensive as well. The goal of our draft it to cover any
> case that can cause the problem of Section 3. We see blind caching of
> on-link determination as a candidate that may cause the problem.
> </hs>
> 
> So, for example, if the proposed text were something like this:
> 
>    Using cached on-link determination information without first
>    verifying that the information is still valid after IPv6 interface
>    re-initialization may lead to lack of IPv6 network connectivity.
> For
>    example, consider the case where a host caches an on-link prefix
>    and leaves the subnet for weeks.  If the network renumbers during
>    the period but the host continues to keep the cached (already
>    invalid) information when it returns, it may lead to a problem
>    described in Section 3 below.
> 
> that would make sense to me.  I'd then be wondering whether this is
> really something to be noted explicitly since it may sound something
> pretty obvious.
> 
> <hs>
> The renumbering may sound obvious to you after we have discussed the
> case of overnight shutdown and vacation and gave a specific example of
> prior and post RA (with PIO and without PIO). Anyway, this is the
> example in the paragraph. The main point is that blind caching of
> on-link determination is not recommended host behavior. We would like
> to keep this text  - your proposed text looks fine to me. We may
> modify your proposed text by giving a specific prior and post RA
> example.
> 
> Further, since RFC4862 and RFC4861 differ in the 2-hour rule for
> address autoconfiguration vs. on-link determination, why is it not OK
> to only mention on-link determination blind caching in our draft and
> not mention any address with blind caching? I am not too strong on
> this one. If we are allowed to keep our text and you still insist we
> add address to blind caching paragraph, I can do that. But note, even
> when we add address to the blind caching paragraph, there is no
> normative text in our paragraph that overrules anything related to
> caching addresses in RFC4862. So why do any host implementors have to
> worry about anything?
> Wes is on vacation till Wednesday next week. My statements here only
> represent me. I need to talk to Erik and Wes too about this one. 
> </hs>
> 
> Hemant
> 
> ---
> JINMEI, Tatuya
> Internet Systems Consortium, Inc.
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