Interface counter errors

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Aug 27th, 2009
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When I run the command "show interface counter errors" I can see an interface with OutDiscards errors. However, when I do the command "show interface" I can't see any problems reported.

Can someone please explain the difference?



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jbrenesj Thu, 08/27/2009 - 12:44
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Outdiscards are a result of too much trying to go out a port at once. Most of the time it

is bursty traffic that overloads the tx buffers for a msec.

I guess you should see output drops on the show interface as well:

sh int g3/x

Input queue: 0/2000/0/0 (size/max/drops/flushes); Total output drops: 25130 <<<<<<<<<<<<<<<<

Can you clear counters and

keep an eye them. What time of day do they go up? What is going out the ports when the

problem is happening? Is there some kind of batch job or something else running with the

counters are increasing?

Hi Dan,

I see the exact same behavior on almost all my 3750 (none G, G, X, ... types) type switches.  I worked with TAC on it and got the answer that this is a purely "display bug only" and can "be ignored".  I did not like this answer.  So I kept digging.  Cisco actually has a guideline / recommended setup for 3750X switches on their website which I find very interesting.  I learned about it during Cisco Live this year and would never have found it otherwise.

I compared this guide to my configuration and noticed the following difference. The default queue settings 3750X generated via Auto QOS look like this:

     mls qos queue-set output 1 threshold 3 100 100 100 400

Here is the same queue setting from the recommendations document (see link above):

     mls qos queue-set output 1 threshold 3 100 100 100 3200

I have implemented this Cisco recommded setting and have seen almost no OutDiscards since.

Hope this helps.



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