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Huge Buffer Misses on Cisco 3550-12G switch

Posted on 2013-12-31
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Last Modified: 2014-01-06
I am seeing buffer misses on my Cisco 3550-12G.  These are not just small, medium, or big buffer misses, they are Huge Buffer misses.  There has been reported slowness on the network and this is the only area on the network at all where I see red flags.  What can I do about the huge buffer misses?  I have over 200 huge buffer misses this hour.
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Question by:denver218
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by:Jordan Medlen
ID: 39748281
Is this "slowness" problem just starting recently? Can you paste "show buffers" and "show int" outputs?

Have you looked at the document... http://www.cisco.com/en/US/products/hw/modules/ps2643/products_tech_note09186a0080093fc5.shtml ? That document may help guide you as to what is occurring.

From the doc...

Misses identifies the number of times that a buffer has been requested and the RP detected in which pool additional buffers were required. In other words, the number of buffers in the free list has dropped below min level. The misses counter represents the number of times the RP has been forced to create additional buffers.
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by:denver218
ID: 39748299
Attached is the output of the "show buffers" and "show int"
show-interface.txt
Show-Buffers.txt
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Jordan Medlen earned 500 total points
ID: 39748368
So looking at your attachments, nothing looks terribly out of the ordinary for a multilayer switch, especially an old one.

Misses are drops, and I see no "failures" in your output, and that's where drops would occur. One thing I do notice is that there are no free huge buffers, which I would expect to see. Could be an indication of a buffer leak there possibly.

Looking at the "sh int" output, nothing glaring there either.

So getting back to the slowness issue, can you provide more feedback on what constitutes "slowness"? Are users complaining of slowness with certain applications? During certain times of day?
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by:denver218
ID: 39751973
What command will allow be to configure the huge buffers?  or should I not even worry about since I have 0 buffer failures?

Certain users have been complaining about intermittent slowness on the internet  and some apps.  I can never replicate the problem.  I'm just going over everything possible to ensure there is nothing wrong.  Internet speeds are fine.  I have 1ms pings all day long to my edge router, I don't have any interface errors.  The only thing I saw were the buffer misses on this switch.
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by:Jordan Medlen
ID: 39752014
An example of how to configure the buffers would be as follows...

From Cisco documentation...

Here are some general values that you can use:

permanent: take the number of total buffers in a pool and add about 20%.

min-free: set min-free to about 20-30% of the permanent number of allocated buffers in the pool.

max-free: set max-free to something greater than the sum of permanents and minimums.

In the buffer tuning example above, we could enter these commands in the global configuration mode:

conf t
buffers huge permanent 180 
buffers huge min-free 50 
buffers huge max-free 230

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Author Closing Comment

by:denver218
ID: 39760088
Thanks.  I just ended up replacing the 3550-12G with a 3750G-12 over the weekend.  It was time to upgrade that switch anyway.  I am no longer seeing any kind of buffer misses.  Thanks.
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