Re: Layer 2 QoS

Thresholds are limits of buffer usage, that when exceeded cause packets
to get discarded.
Examples usually show higher values on higher ids, in the 3560
the threshold 3 fixed at 100%.
(Meaning you drop when there is absolutelly no place to hold the packet)
Having a 50% threshold would discard even though you have half of the
buffers available.

 From where do you get the impression that higher thresholds are more
drop prone ?

-Carlos

Diment, Andrew @ 27/02/2011 17:23 -0300 dixit:
> I have a quick questions on layer 2 QoS that I cannot find an answer to. In
> all of cisco's doc and QoS design guides they map higher COS traffic (or DSCP
> traffic) to higher thresholds within the queues like below.
>
> mls qos srr-queue output cos-map queue 2 threshold 1 2
> mls qos srr-queue output cos-map queue 2 threshold 2 3
> mls qos srr-queue output cos-map queue 2 threshold 3 6 7
>
> My understanding of thresholds is the higher the threshold breached the more
> likely packets get dropped. The way Cisco says do to this mapping seem
> opposite to me. I would think you would want the more critical traffic in the
> lower threshold...not the higher. I know COS 5 goes to the priority queue so
> I'm just looking at the non-priority queues.
>
> Thanks,
> Andy
>
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-- 
Carlos G Mendioroz  <tron_at_huapi.ba.ar>  LW7 EQI  Argentina
Blogs and organic groups at http://www.ccie.net