[c-nsp] Constant output drops on etherchannel

[Nick Hilliard]

On 16/01/2011 23:27, Dan Letkeman wrote:
> Thanks for the detailed explanation.
>
> The problem is I also see this on our gig switches as well.  And only
> on ether channel's, not on a single interconnects.  The traffic can be
> a such a minimum and I still see drops.

This is all microbursts.   Your traffic is obviously very bursty.  Tune 
your has algorithm and see if it helps.

> I would like to tune the output buffers, but I'm not sure where to
> start.  I know that I need to learn some more about qos, because we do
> have a voice network that is growing very fast.
>
> Do you know of some good documentation or books that I can start with?

3750 QoS is explained in great detail here:

http://www.cisco.com/en/US/docs/switches/lan/catalyst3750/software/release/12.2_55_se/configuration/guide/swqos.html

But also, this document is well worth reading:

https://supportforums.cisco.com/docs/DOC-8093

(thanks to Saku Ytti for this link).

Just bear in mind that the 3750/3560 switch range has miserably small 
buffers, so you really have very little to play with.  You would be well 
advised to figure out where these microbursts come from.

Also, probably not a bad idea to configure "load interval 30" on all 
affected interfaces, and if you have a load graphing system which supports 
< 5 minute intervals, set it to 30 seconds and see what happens (this is 
not guaranteed to provide accurate results, btw).

Nick