Subject: [Tsvwg] Re: draft-ietf-tsvwg-quickstart-00: Consideration of QS NONCE.

From: Sally Floyd <[email-masked]>
Date: Mon, 29 Aug 2005 10:12:41 -0700

>> My inclination would be to say that the sender MAY decide to only
>> accept a QS response with a valid nonce (indicating the approval by
>> the routers of the original rate request), and that when a rate
>> request is downgraded in the network, the sender MAY send a new QS
>> request with the downgraded value to see if this is in fact approved
>> with a valid nonce returned in the response.
>
>I am not sure this sort of loose approach is advisable.  (In other
>words, with no change in the routers I am not sure this is a reasonable
>path for senders to take.)

Well, we already agree (I assume) that "the sender MAY decide to only
accept a QS response with a valid nonce".  So the question is whether
we want to say that the sender MAY send a new QS request with a 
downgraded value, or whether we want to discourage such a behavior.
Or just say nothing about it one way or another.  I could be 
perfectly happy with any of these choices.

My assumption is that in one of the initial deployment scenarios, that
of Intranets, there will be a fair amount of trust between senders
and receivers, and the nonce won't be needed one way or another.

Another of the possible initial deployment scenarios is that of
GPRS networks, and I would guess that the nonce wouldn't be needed
in this scenario either, because the initial request rates won't be
all that large in the first place (e.g., 320 Kbps).  

But perhaps another initial deployment scenario would be a 10Gbps
global network, where initial request rates might be quite large,
but there is a wide enough set of users that senders don't necessarily
trust receivers, and senders will rely on the nonce.  If a QS
request is approved but downgraded in the network, would senders
want to send a new QS request, for a lower rate, to see if the lower
rate is approved as is in the network?  Perhaps, if the resent QS
request seems worth the wait.  Perhaps in such an environment the
routers in the network would keep track of large Quick-Start requests,
and know how to deal with resent QS requests, so that they are likely
to be approved.

So one possibility would be to say that "the sender MAY send a new
QS request with the downgraded value", and to be clear about all
of the reasons why this might not be a good idea, and to say that
we hope for experience to learn what to recommend in the Proposed
Standard version of Quick-Start (assuming that Quick-Start at some
point makes it that far).

?

- Sally

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From: Mark Allman <[email-masked]>
Date: Mon, 29 Aug 2005 13:27:38 -0400

> accept a QS response with a valid nonce".

Um.  Well, of course, this doesn't sound so bad on its own.  And, I am
comfortable with it.  But, when taken with ...

> So the question is whether we want to say that the sender MAY send a
> new QS request with a downgraded value, or whether we want to
> discourage such a behavior.  Or just say nothing about it one way or
> another.  I could be perfectly happy with any of these choices.

Right.  

So, I'd be happy to hear other opinions on this.

As I said, I am completely unconvinced in this entire nonce idea.
Without Gorry's tweak it just seems like weak protection and with
Gorry's tweak it seems like it requires a lot of help and complicates
the whole thing.  I am not yet sure if we need such complication.  Maybe
we do.

I wonder if we could just rip the nonce out of the normative portion of
the document, leave the 4 bits as "reserved" and add an appendix which
is "possible use of a nonce" and all these questions could be noted for
folks to think about.  That seems to get the main QS stuff (the rate
request) out the door without nailing down the extra bits to the nonce
quite yet since it seems like a thorny question that could maybe use
some work to puzzle through.  But, at the same time, we can record the
thinking we have all done about the nonce thus far.  Is that a useful
path?

Thanks,
allman