[c-nsp] 3750-x output drops

[Richard N. Ingram]

On Thu, Nov 17, 2011 at 06:05:06PM +0000, marc williams wrote:
> Yep it's a module. We see the drops sporadically. The outbound traffic level is a fairly steady 100mbit when we see drops. We are polling at 1 minute intervals and don't see a corresponding burst in traffic. Maybe microbursts?
> 
> 

Yes, I would say that's most likely.  Small buffers + microbursts
= drops.  There was a good thread on this earlier this year:

http://www.gossamer-threads.com/lists/cisco/nsp/150484

And here's a good paper referenced in that thread:

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

Best regards,
Rich


> Sent from my iPhone
> 
> On 17 Nov 2011, at 17:26, "Richard N. Ingram" <rich at ferlie.org> wrote:
> 
> > On Thu, Nov 17, 2011 at 12:19:48PM +0000, marc williams wrote:
> >> Can anyone shed light onto what is/goes to Queue 3 Weight 2. This is where we see the drops. No QoS on this switch.
> >> This switch is a:
> >> WS-C3750X-48       12.2(55)SE            C3750E-IPBASEK9-M    
> >> 
> >> 
> >> show platform port-asic stats drop gigabitEthernet 4/1/4 
> >> 
> >>   Interface Gi4/1/4 TxQueue Drop Statistics
> >>     Queue 0
> >>       Weight 0 Frames 0
> >>       Weight 1 Frames 0
> >>       Weight 2 Frames 0
> >>     Queue 1
> >>       Weight 0 Frames 0
> >>       Weight 1 Frames 0
> >>       Weight 2 Frames 0
> >>     Queue 2
> >>       Weight 0 Frames 0
> >>       Weight 1 Frames 0
> >>       Weight 2 Frames 0
> >>     Queue 3
> >>       Weight 0 Frames 0
> >>       Weight 1 Frames 0
> >>       Weight 2 Frames 438
> >> 
> > 
> > It looks like you're using a network module.  I don't have one handy to look at, but Queue 3 Weight 2 is probably where all your traffic is going.  If QOS is off, everything goes into that queue.  So if you're overrunning your gig. interface, those are your drops.  Other queues are used by the switch, even with QOS off, for things like BPDUs.  If you look at "show platform port-asic stats enqueue gx/x/x" you'll see some hits on other queues as well, but very minimal numbers compared to your actual user traffic.
> > 
> > Hope that helps,
> > Rich