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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 at isc.org'; Wes Beebee (wbeebee)
Cc:
Suresh Krishnan; Thomas Narten; Brian Haberman; Bob
Hinden; ipv6 at 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 at isc.org [mailto:Jinmei_Tatuya at 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 at 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 at 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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