output drops on interface withiout congestion

[carlos.v2015]

hi,

i have a 7600 with WS-X6748-GE-TX. I have a port-cannel  (4x1G) to cmts, i´m seeing a lot of Total output drops. This drops i see in each interface of the channel. The total traffic on channel is 1,2 gbps, so the traffic for interface is  300 Mbps (peak hour).

When i see the queueing, all the drops are in queue 1 (cos 0).

What can i do to eliminate the drops ?

#sh int port-channel 121 | in rate
  Queueing strategy: fifo
  30 second input rate 42881000 bits/sec, 25824 packets/sec
  30 second output rate 607609000 bits/sec, 60330 packets/

#sh int Gi3/35 | in rate               
  Queueing strategy: fifo
  5 minute input rate 10067000 bits/sec, 6387 packets/sec
  5 minute output rate 167940000 bits/sec, 16241 packets/sec
Temuco_7609#

sh queueing interface Gi3/35

   WRR bandwidth ratios:  100[queue 1] 150[queue 2] 200[queue 3]
    queue-limit ratios:     50[queue 1]  20[queue 2]  15[queue 3]  15[Pri Queue]

  Packets dropped on Transmit:

    queue     dropped  [cos-map]
    ---------------------------------------------
    1                  7032114  [0 1 ]
    2                        0  [2 3 4 ]
    3                        0  [6 7 ]
    4                        0  [5 ]

regards,

Carlos

[Joseph W. Doherty]

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Posting

How to try to remediate the drops depends on the cause of the congestion.  Increasing Q1's bandwidth or queue-limit ratios might decrease its drops although at the chance of increasing drops in other queues.

You say you have a 4x port channel - how's the distribution load across the ports?  If uneven, perhaps there's a better hash algorithm for your traffic.

Lastly, sometime you need more bandwidth or a "better" line card.  (Not sure you'll find much better than a 6748 for gig usage.)

[carlos.v2015]

hi,

in the channel the distribution across all ports is uniform.

The interfaces are not congested and I always see drops.

regards,

Carlos

[Joseph W. Doherty]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages wha2tsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

If there were no congestion, there shouldn't be drops.

What often happens, microbursts cause millisecond congestion, which may cause drops, but multi-second monitoring doesn't see these.

[carlos.v2015]

in peak hour each interface have 2 errors/sec.

so in the channel show 10 errors/sec.

I attached a graph of errors in the channel.

[Joseph W. Doherty]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

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In no event shall Author be liable for any damages wha2tsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

The number of discards a second, alone, means nothing.  You need to compare to the volume of traffic at the same time.