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Qos issue, understanding

Hi,

this is regarding a config of a 3750 with qos. The customer had programmed the 3750 like a 3550, so the priority queue was wrong.

3550 queue 4 is PQ

3750 queue 1 is PQ.

cos 0 and 1 was mapped to queue 1.

The behavior of the output on the 3750 was that the output was only 6 mbit/sek when priority queue on the interface was disabled.

When I enabled priority queue on the interface it was normal.

My question is why the speed was only 6 mbit/s output ?

I have copied the config below,but can someone please explain the behavior of these commands on the interface:

srr-queue bandwidth share 10 20 40 80

srr-queue bandwidth shape 0 0 0 0

the share cmd would give 10/(10+20+40+80) = ca 6 % bw. But the cisco doc says this is guaranted, not limited...

There are also some other tings in this cofig that I find strange, mapping etc.

any ideas ?

BR

Runar

config:

mls qos map dscp-cos 16 to 1

mls qos map dscp-cos 24 to 2

mls qos map dscp-cos 32 to 3

mls qos map dscp-cos 40 to 4

mls qos map cos-dscp 0 10 18 26 34 46 48 56

mls qos srr-queue input bandwidth 25 75

mls qos srr-queue input threshold 1 40 40

mls qos srr-queue input buffers 50 50

mls qos srr-queue input priority-queue 2 bandwidth 25

mls qos srr-queue input cos-map queue 2 threshold 2 4 5 6 7

mls qos srr-queue input dscp-map queue 1 threshold 2 10 11 12 13 14 26 27 28

mls qos srr-queue input dscp-map queue 1 threshold 2 29 30

mls qos srr-queue input dscp-map queue 2 threshold 1 39 48 49 50 51 52 53 54

mls qos srr-queue input dscp-map queue 2 threshold 1 55 56 57 58 59 60 61 62

mls qos srr-queue input dscp-map queue 2 threshold 1 63

mls qos srr-queue input dscp-map queue 2 threshold 2 34 35 36 37 38

mls qos srr-queue output cos-map queue 1 threshold 1 0 1

mls qos srr-queue output cos-map queue 2 threshold 1 2 3

mls qos srr-queue output cos-map queue 3 threshold 2 4

mls qos srr-queue output cos-map queue 4 threshold 2 5 6 7

mls qos srr-queue output dscp-map queue 1 threshold 1 0 1 2 3 4 5 6 7

mls qos srr-queue output dscp-map queue 1 threshold 1 8 9 15 16 17

mls qos srr-queue output dscp-map queue 1 threshold 2 10 11 12 13 14

mls qos srr-queue output dscp-map queue 2 threshold 1 18 19 20 21 22 23 24 25

mls qos srr-queue output dscp-map queue 2 threshold 1 31 32 33

mls qos srr-queue output dscp-map queue 2 threshold 2 26 27 28 29 30

mls qos srr-queue output dscp-map queue 3 threshold 1 39 40 41 42 43 44 45

mls qos srr-queue output dscp-map queue 3 threshold 2 34 35 36 37 38

mls qos srr-queue output dscp-map queue 4 threshold 1 46 47

mls qos queue-set output 1 threshold 1 40 100 100 100

mls qos queue-set output 1 threshold 2 40 100 100 100

mls qos queue-set output 1 threshold 3 40 100 100 100

mls qos queue-set output 1 threshold 4 40 100 100 100

mls qos

1 REPLY
Silver

Re: Qos issue, understanding

Use the srr-queue bandwidth shape interface configuration command on the switch stack or on a standalone switch to assign the shaped weights and to enable bandwidth shaping on the four egress queues mapped to a port. Use the no form of this command to return to the default setting.

srr-queue bandwidth shape weight1 weight2 weight3 weight4

no srr-queue bandwidth shape

This command is not available on a 10-Gigabit Ethernet interface.

Specify the weights to specify the percentage of the port that is shaped. The inverse ratio (1/weight) specifies the shaping bandwidth for this queue. Separate each value with a space. The range is 0 to 65535.

Weight1 is set to 25. Weight2, weight3, and weight4 are set to 0, and these queues are in shared mode.

In shaped mode, the queues are guaranteed a percentage of the bandwidth, and they are rate-limited to that amount. Shaped traffic does not use more than the allocated bandwidth even if the link is idle. Use shaping to smooth bursty traffic or to provide a smoother output over time.

The shaped mode overrides the shared mode.

If you configure a shaped queue weight to 0 by using the srr-queue bandwidth shape interface configuration command, this queue participates in shared mode. The weight specified with the srr-queue bandwidth shape command is ignored, and the weights specified with the srr-queue bandwidth share interface configuration command for a queue come into effect.

When configuring queues for the same port for both shaping and sharing, make sure that you configure the lowest numbered queue for shaping.

The egress queue default settings are suitable for most situations. You should change them only when you have a thorough understanding of the egress queues and if these settings do not meet your QoS solution.

This example shows how to configure the queues for the same port for both shaping and sharing. Because the weight ratios for queues 2, 3, and 4 are set to 0, these queues operate in shared mode. The bandwidth weight for queue 1 is 1/8, which is 12.5 percent. Queue 1 is guaranteed this bandwidth and limited to it; it does not extend its slot to the other queues even if the other queues have no traffic and are idle. Queues 2, 3, and 4 are in shared mode, and the setting for queue 1 is ignored. The bandwidth ratio allocated for the queues in shared mode is 4/(4+4+4), which is 33 percent:

Switch(config)# interface gigabitethernet2/0/1

Switch(config-if)# srr-queue bandwidth shape 8 0 0 0

Switch(config-if)# srr-queue bandwidth share 4 4 4 4

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