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

"Azinger, Marla" <marla.azinger@frontiercorp.com> Wed, 30 July 2008 14:15 UTC

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From: "Azinger, Marla" <marla.azinger@frontiercorp.com>
To: "Wes Beebee (wbeebee)" <wbeebee@cisco.com>, "Hemant Singh (shemant)" <shemant@cisco.com>, "Jinmei_Tatuya@isc.org" <Jinmei_Tatuya@isc.org>
Date: Wed, 30 Jul 2008 10:14:08 -0400
Subject: RE: 6MAN WG Last Call:draft-ietf-6man-ipv6-subnet-model-00.txt
Thread-Topic: 6MAN WG Last Call:draft-ietf-6man-ipv6-subnet-model-00.txt
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Hello-

This may be nit picky but I have a request to change the title of this document.

Reason why is because in my world and around the RIR's when someone says "subnet model" it actually refers to a model of subnetting plans and diagrams.

Could this title possibly be changed to directly reflect what exactly its about?

For example:

IPv6 Prefix and its effect on Link-Local

or

IPV6 Prefix Cause and Effect on Links

Thank you for considering this change

Marla Azinger
Frontier Communications

________________________________
From: ipv6-bounces@ietf.org [mailto:ipv6-bounces@ietf.org] On Behalf Of Wes Beebee (wbeebee)
Sent: Friday, July 25, 2008 6:45 AM
To: Hemant Singh (shemant); Jinmei_Tatuya@isc.org
Cc: Thomas Narten; ipv6@ietf.org; Brian Haberman; Bob Hinden; Suresh Krishnan
Subject: RE: 6MAN WG Last Call:draft-ietf-6man-ipv6-subnet-model-00.txt


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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