On 30/08/13 15:49, Victor Lyapunov wrote:
Hello all
Got a question about queuing functionality in WS67xx cards. We have a
typical 7609 setup with TenG uplink and GigE downlink interfaces.
During the day we see an increase in packet drops on the GigE downlink
interfaces. The average bandwidth is kept around 750Mbps but I suppose
short bursts may result in dropped packets. Is there any way to improve
this behavior? (e.g increase output buffer?)
Since you've got QoS enabled, you need to pay attention to:
1. The division of the buffer space between queues
2. The RED drop threshold(s) within those queues
3. What queues your QoS config has traffic being put into
Why do you have QoS enabled? Is it just for CoPP? If so, all your
traffic will be going into queue 1, and the default config only gives it
a fraction of the total buffer space, and 70% drop threshold. You can
see this in your "sh queueing" output:
lab7609#sh mls qos queuing interface g1/22
Weighted Round-Robin
Port QoS is enabled
Trust state: trust DSCP
Extend trust state: not trusted [COS = 0]
Default COS is 0
Queueing Mode In Tx direction: mode-cos
Transmit queues [type = 1p3q8t]:
Queue Id Scheduling Num of thresholds
-----------------------------------------
01 WRR 08
02 WRR 08
03 WRR 08
04 Priority 01
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]
^^^ pay close attention to the above values
queue tail-drop-thresholds
--------------------------
1 70[1] 100[2] 100[3] 100[4] 100[5] 100[6] 100[7] 100[8]
2 70[1] 100[2] 100[3] 100[4] 100[5] 100[6] 100[7] 100[8]
3 100[1] 100[2] 100[3] 100[4] 100[5] 100[6] 100[7] 100[8]
...and these ^^^
Is the output queue (even when we enable mls qos) 40 packets long (have
read that Tx buffer length is around 1Mbyte)?
I don't know where you got "40" from, but the thresholds are in % and
the weights are unitless.
In mls mode can we configure its length using "hold-queue <len>" ?
No.
The traffic in our network is mostly best effort (not care much about
additional delay). Is there a way to decrease output packet drops
for WS67xx cards operating in mls qos?
Yes, assign more queue to the BE queue.
(If this has already been addressed in the past please provide reference to
previous thread)
This has been discussed lots of times, and I'm not about to spend time
googling - you can do that!
See also:
http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/ios/12.2SX/configuration/guide/qos.html
http://www.cisco.com/en/US/docs/solutions/Enterprise/WAN_and_MAN/QoS_SRND/QoSDesign.html#wp1000574
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