Qos on 3750 switchs

[Driss BENATTOU]

Hi,

Taking the lines below :

mls qos srr-queue output cos-map queue 2 threshold 1  4
mls qos srr-queue output cos-map queue 2 threshold 3  6 7

it's a template that i find at lot of examples of config.

what is the criteria that define if the cos value will be affected to threshold 1 or threshold 3

Thanks at advance

Regards

[Daniele Giordano]

The below document explains all:

mls qos srr-queue output cos-map

Use the mls qos srr-queue output cos-map global  configuration command on the switch stack or on a standalone switch to  map class of service (CoS) values to an egress queue or to map CoS  values to a queue and to a threshold ID. Use the no form of this command to return to the default setting.

mls qos srr-queue output cos-map queue queue-id {cos1...cos8 | threshold threshold-id cos1...cos8}

no mls qos srr-queue output cos-map

Syntax Description

queue queue-id	Specify a queue number. For queue-id, the range is 1 to 4.
cos1...cos8	Map CoS values to an egress queue. For cos1...cos8, enter up to eight values, and separate each value with a space. The range is 0 to 7.
threshold threshold-id cos1...cos8	Map CoS values to a queue threshold ID. For threshold-id, the range is 1 to 3. For cos1...cos8, enter up to eight values, and separate each value with a space. The range is 0 to 7.

Examples

This example shows how to map a port to queue-set 1. It maps CoS values 0  to 3 to egress queue 1 and to threshold ID 1. It configures the drop  thresholds for queue 1 to 50 and 70 percent of the allocated memory,  guarantees (reserves) 100 percent of the allocated memory, and  configures 200 percent as the maximum memory that this queue can have  before packets are dropped.

Switch(config)# mls qos srr-queue output cos-map queue 1 threshold 1 0 1 2 3

Switch(config)# mls qos queue-set output 1 threshold 1 50 70 100 200

Switch(config)# interface gigabitethernet2/0/1

Switch(config-if)# queue-set 1

[Driss BENATTOU]

Hi,

thank you for raply but it doesn't match my request.

we suppose we have the following question :

Put      COS 5 in the priority queue

queue 2 4,6,7

queue 3 2,3

queue 4 0

you find the following in the answer :

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

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

....

taking only the example of queue 2, why we put 4 in threshold 3 and not all 4,6 anf 7 into the same threshold ???

I hope that you can understand well my question

Regards

Driss

[Daniele Giordano]

This is your choice.

Probably in this example, frames with cos 6 and 7 are "more important" of frames with cos 4 and so are assigned threshold that guarantees major availability of buffers an memory.

mls qos queue-set output threshold

Use the mls qos queue-set output threshold global  configuration command on the switch stack or on a standalone switch to  configure the weighted tail-drop (WTD) thresholds, to guarantee the  availability of buffers, and to configure the maximum memory allocation  to a queue-set (four egress queues per port). Use the no form of this command to return to the default setting.

mls qos queue-set output qset-id threshold queue-id drop-threshold1 drop-threshold2  reserved-threshold maximum-threshold

no mls qos queue-set output qset-id threshold [queue-id]

Syntax Description

qset-id	ID of the queue-set. Each port belongs to a queue-set, which defines all  the characteristics of the four egress queues per port. The range is 1  to 2.
queue-id	Specific queue in the queue-set on which the command is performed. The range is 1 to 4.
drop-threshold1 drop-threshold2	Two WTD thresholds expressed as a percentage of the queue's allocated memory. The range is 1 to 400 percent.
reserved-threshold	Amount of memory to be guaranteed (reserved) for the queue and expressed  as a percentage of the allocated memory. The range is 1 to 100 percent.
maximum-threshold	Enable a queue in the full condition to obtain more buffers than are  reserved for it. This is the maximum memory the queue can have before  the packets are dropped. The range is 1 to 400 percent.

Defaults

When quality of service (QoS) is enabled, WTD is enabled.

Table 2-9 shows the default WTD threshold settings.

Table 2-9     Default Egress Queue WTD Threshold Settings

Feature	Queue 1	Queue 2	Queue 3	Queue 4
WTD Drop Threshold 1	100 percent	50 percent	100 percent	100 percent
WTD Drop Threshold 2	100 percent	50 percent	100 percent	100 percent
Reserved Threshold	50 percent	100 percent	50 percent	50 percent
Maximum Threshold	400 percent	400 percent	400 percent	400 percent

[Driss BENATTOU]

Hi,

Sometimes we said that when queue 2 reaches 60 % we start dropping cos 4 packets and you see :

mls qos queue-set output 2 threshold 2 40 60 100 100

why  the values for first threshold, reserved and maximum threshold are changed.

I can see why ?

Please explain more.

Regards

Driss

[Daniele Giordano]

I don't clearly understand your question.

Threshold values are presetted globaly on 3750.

If you want show them use:

sh mls qos input-queue

Queue     :       1       2

----------------------------------------------

buffers   :      90      10

bandwidth :       4       4

priority  :       0      20

threshold1:     100     100

threshold2:     100     100

sh mls qos queue-set

Queueset: 1

Queue     :       1       2       3       4

----------------------------------------------

buffers   :      25      25      25      25

threshold1:     100     200     100     100

threshold2:     100     200     100     100

reserved  :      50      50      50      50

maximum   :     400     400     400     400

Queueset: 2

Queue     :       1       2       3       4

----------------------------------------------

buffers   :      25      25      25      25

threshold1:     100     200     100     100

threshold2:     100     200     100     100

reserved  :      50      50      50      50

maximum   :     400     400     400     400

To see the queuing strategy of a specific interface use

sh queueing interface f1/0/1
Interface FastEthernet1/0/1 queueing strategy: fair
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: weighted fair
  Output queue: 0/1000/64/0 (size/max total/threshold/drops)
     Conversations  0/1/256 (active/max active/max total)
     Reserved Conversations 0/0 (allocated/max allocated)
     Available Bandwidth 75000 kilobits/sec

This is my QoS configuration:

mls qos srr-queue input priority-queue 2 bandwidth 20
mls qos srr-queue input cos-map queue 1 threshold 3 0 1 2 3 4
mls qos srr-queue input cos-map queue 2 threshold 3 5 6 7
mls qos srr-queue output cos-map queue 1 threshold 3 5 6 7
mls qos srr-queue output cos-map queue 2 threshold 3 4
mls qos srr-queue output cos-map queue 3 threshold 3 2 3
mls qos srr-queue output cos-map queue 4 threshold 3 0 1
mls qos

Regards.