Subject: Re: [Diffserv] EF RFC and loss

From: [email-masked]
Date: Thu, 28 Oct 1999 16:39:28 +0200

Brian,

You are certainly correct that any queuing system has a
finite probability that the queue size exceeds the buffer
size; the point of EF is that a correctly engineered premium
service will reduce this probability to a negligible level.

However, there is one fundamental point that applications
designers must not overlook: differentiated services change
the statistics, but they do not change the fact that every
IP packet has a finite probability of being dropped.

[manu] Thanks for the above but I still miss an important piece for a complete answer.
Namely, if the packet loss has a finite (be it negligible) probability, why should
it trigger the notion of "possible attacks or serious misconfiguration" as explicited
in the RFC security section.

   Brian

manu

[email-masked] wrote:
>
> >On Thu, 28 Oct 1999 [email-masked] wrote:
>
> >
> >
> > Folks,
> >
> > The EF PHB RFC 2598 states at the end of section 3 on Security considerations:
> >
> > "Similarly, since the aggregate EF traffic rate is constrained at
> > every interior node, the EF queue should never overflow so if it
> > does the drops SHOULD be noted as possible attacks or serious misconfiguration."
> >
> > Does this mean that the EF PHB specifically requires "absolute zero" packet loss due to buffer overflow?
> > I  was under the impression that a statistical packet queueing process always entailed a loss probability,
> > that can however  be engineered to a low but non-zero value.
> >
> > Thanks in advance for any clarifiaction,
> >
> > manu
> >
> To my understanding loss of packets in EF is an exceptional condition.
> Scheduling schemes (PQ, WRR or CBQ) used to implement EF do provide the
> behaviour as defined in EF rfc.
>
> [manu] But you admit that they genuinely occur be it rarely/occasionaly.
> So why should this be seen as a potential "attack or serious misconfiguration"?
>
> <snip>
>
> with Regards
>
> [manu] And mine,
>
> Anurag,
>
> manu
> ---------------------------------------------
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> >
> >
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> >
> >
>
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--
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Brian E Carpenter (IAB Chair)
Program Director, Internet Standards & Technology, IBM
On assignment for IBM at http://www.iCAIR.org
Non-IBM email: [email-masked]