[c-nsp] ASIC to switch port mapping

[Gert Doering]

Hi,

On Fri, Sep 10, 2010 at 01:18:19PM -0400, Vincent Aniello wrote:
> I am trying to solve a output drops on switch ports on which bandwidth
> utilization does not seem to exceed the port speed.  Seems like the
> drops are due to the buffers filling up and dropping frames.  I am under
> the impression that each ASIC has their own buffer and if the buffer
> fills on a particular ASIC all ports that share that ASIC will also drop
> frames.  If I know the switch interfaces associated with each ASIC I can
> redistribute the connections on the switch to better balance the load.

There's material in the c-nsp archives about the buffer size issue on the
2960, 3560 and related switches.  Short answer: the buffers are so tiny that
Cisco doesn't even document the size anywhere.  So as soon as you have
microburst traffic with "more ingress ports than egress", you'll see drops
(turn on QoS, cut the buffers into 4 even smaller queues, increase(!) drops).

Cisco does not think that this is a problem, and I have been told that the 
new generation 2960S and 3560E have the same size buffers.

gert
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USENET is *not* the non-clickable part of WWW!
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Gert Doering - Munich, Germany                             gert at greenie.muc.de
fax: +49-89-35655025                        gert at net.informatik.tu-muenchen.de
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