01-03-2011 04:25 PM - edited 03-06-2019 02:48 PM
Hi Experts,
I need to configure these qos settings in a C2960S
interface range GigabitEthernet1/0/1 - 48
priority-queue out
service-policy input QoS_Standard
srr-queue bandwidth share 10 30 6 54
How I calculate the buffer allocation needed?
mls qos queue-set output 2 buffers X Y Z T
mls qos queue-set output 2 threshold 1 A B C D
mls qos queue-set output 2 threshold 2 E F G H
mls qos queue-set output 2 threshold 3 I J K M
mls qos queue-set output 2 threshold 4 N L O P
MODEL; WS-C2960S-48LPS-L
IOS: c2960s-universalk9-mz.122-53.SE2.bin
Thank you in advance
Solved! Go to Solution.
01-03-2011 06:05 PM
Hi Marcos,
Command 'srr-queue bandwidth share" doesnt allocate the buffer for each queue. It assigns the weight for each queue. The buffer size for each queue is configured by 'mls qos queue-set output queue-id' command. Please refer the configuration guide for detail explanation.
HTHs,
Lei Tian
01-05-2011 06:01 AM
Hi Marcos,
The bandwidth share command is used to assign the weight for each queue; it controls how many packets each queue can forward in every interval. That is related to the amount of traffic you expect from each class. The mls qos queue-set output 2 buffers command is to configure the queue size for each queue; it controls how many packets each queue can hold. The mls qos queue-set output 2 threshold command controls when one particular queue starts drop packets.
There is no formula to calculate buffer size, but there is some general guidelines you can follow.
1,Set the threshold percentages levels higher than 100, so no packets are dropped before reserved buffer is full.
2, Avoid increase the “reserved” buffer for a given tx queue, because that will decrease common buffer pool.
3,Consider increasing the thresholds and the maximum before modifying the buffers and reserved buffer.
4, Modify the buffer size will affect all interfaces using same queue-set; so, you can consider use different queue-set for ports have different traffic pattern.
Based on the guidelines, you can use the following as the starting point, and adjust the value from there.
mls qos queue-set output 2 buffers 10 25 10 55
mls qos queue-set output 2 threshold 1 150 300 100 400
mls qos queue-set output 2 threshold 2 150 300 50 400
mls qos queue-set output 2 threshold 3 150 300 50 400
mls qos queue-set output 2 threshold 4 200 300 100 400
HTH,
Lei Tian
01-03-2011 06:05 PM
Hi Marcos,
Command 'srr-queue bandwidth share" doesnt allocate the buffer for each queue. It assigns the weight for each queue. The buffer size for each queue is configured by 'mls qos queue-set output queue-id' command. Please refer the configuration guide for detail explanation.
HTHs,
Lei Tian
01-04-2011 12:34 AM
Hi Lei,
Thank you for your answer. I know that command 'srr-queue bandwidth share" doesnt allocate the buffer for each queue. I just want to know how to calculate the proper values of (X Y Z T A B C D E F G H I J K M N L O P ) to meet my needs (srr-queue bandwidth share 10 30 6 54)
mls qos queue-set output 2 buffers X Y Z T
mls qos queue-set output 2 threshold 1 A B C D
mls qos queue-set output 2 threshold 2 E F G H
mls qos queue-set output 2 threshold 3 I J K M
mls qos queue-set output 2 threshold 4 N L O P
Thank you.
01-05-2011 06:01 AM
Hi Marcos,
The bandwidth share command is used to assign the weight for each queue; it controls how many packets each queue can forward in every interval. That is related to the amount of traffic you expect from each class. The mls qos queue-set output 2 buffers command is to configure the queue size for each queue; it controls how many packets each queue can hold. The mls qos queue-set output 2 threshold command controls when one particular queue starts drop packets.
There is no formula to calculate buffer size, but there is some general guidelines you can follow.
1,Set the threshold percentages levels higher than 100, so no packets are dropped before reserved buffer is full.
2, Avoid increase the “reserved” buffer for a given tx queue, because that will decrease common buffer pool.
3,Consider increasing the thresholds and the maximum before modifying the buffers and reserved buffer.
4, Modify the buffer size will affect all interfaces using same queue-set; so, you can consider use different queue-set for ports have different traffic pattern.
Based on the guidelines, you can use the following as the starting point, and adjust the value from there.
mls qos queue-set output 2 buffers 10 25 10 55
mls qos queue-set output 2 threshold 1 150 300 100 400
mls qos queue-set output 2 threshold 2 150 300 50 400
mls qos queue-set output 2 threshold 3 150 300 50 400
mls qos queue-set output 2 threshold 4 200 300 100 400
HTH,
Lei Tian
11-06-2011 06:53 PM
Hello Lei Tian,
As we have the same issue with our network, I have been reading a lot of posts on the packet drops on the egress queues after the deployment of QoS on 2960/3560/3750 switches and I felt that your posts are so much valuable for me to understand this issue further. However, I still have a few questions to be answered as below.
1. In my opinion, it doesn't make sense that the switch drops packets on the egress queues while there still exists bandwidth available for the port. However, I have been experiencing packet drops on the egress queues even the traffic on the whole physical interface(100Mbps) reaches less than 15Mb/sec. It is something I really cannot explain in my knowledge. In my opinion, the switch port should not drop packets unless there is congestion on the physical interface. Would you help explain why the swich would drop packets even there is only about 15Mbit/sec traffic?
2. Is it the only way to address the issue of packet drops while under-subscribed that we have to fine tune the numbers for SRR weight, buffers,and the thresholds for each queue?
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