QoS initial config help

trptplayer1 · ‎07-19-2007

Hi. Please forgive my lack of knowledge regarding QoS, but I must ask for help. I am supposed to get QoS configured on 11 switches at an elementary school in our district. An engineer has been hired to set it up at the other buildings as they were part of a construction contract with new equipment. This equip. was new in December and as a result not part of this contract. The switches we have at this school are: 1 - Cat3750 - Core switch; 4 - Cat3560 - Access switches; 4 - Cat3550 switches - Access switches; 2 - Cat2950 - Access switches. The phones will obviously be plugging into PoE ports into their various switches. Here is an example of what I have on a 3560 switch so far.

!

mls qos map cos-dscp 0 8 16 24 32 46 48 56

mls qos map ip-prec-dscp 0 8 16 24 32 46 48 56

mls qos

!

no file verify auto

!

spanning-tree mode rapid-pvst

no spanning-tree optimize bpdu transmission

spanning-tree extend system-id

!

vlan internal allocation policy ascending

!

interface FastEthernet0/1

description VLAN 110: IP phone

switchport access vlan 110

switchport mode access

priority-queue out

mls qos trust dscp

spanning-tree portfast

!

interface FastEthernet0/2

description VLAN 110: IP phone

switchport access vlan 110

switchport mode access

priority-queue out

mls qos trust dscp

spanning-tree portfast

If anyone is willing to help, God Bless You! I don't believe any of this actually shapes the traffic. All of the above config simply prepares the switches to allow/trust the traffic from the devices. Is this correct?

Any help is appreciated!

Thanks,

Dan

royalblues · ‎07-19-2007

yes the config simply allows the switch to trust the settings sent by the device.

I would have also tuned the queue settings on the switch.

eg on 3560

mls qos

!

mls qos map cos-dscp 0 8 18 26 34 46 48 56

!

mls qos srr-queue output cos-map queue 1 threshold 3 5

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

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

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

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

mls qos srr-queue output cos-map queue 4 threshold 3 0

mls qos srr-queue output cos-map queue 4 threshold 1 1

!

mls qos srr-queue output dscp-map queue 1 threshold 3 46 40

mls qos srr-queue output dscp-map queue 2 threshold 3 48 56

mls qos srr-queue output dscp-map queue 2 threshold 2 24 26 28 30

mls qos srr-queue output dscp-map queue 2 threshold 1 32 34 36 38

mls qos srr-queue output dscp-map queue 3 threshold 3 16 18 20 22

mls qos srr-queue output dscp-map queue 4 threshold 3 0

mls qos srr-queue output dscp-map queue 4 threshold 1 8 10

!

mls qos queue-set output 1 threshold 2 75 85 50 400

mls qos queue-set output 1 threshold 4 15 100 50 400

interface g1/0/1

mls qos trust dscp

queue-set 1

srr-queue bandwidth share 1 39 24 37

srr-queue bandwidth shape 5 0 0 0

priority-queue out

HTH

Narayan

trptplayer1 · ‎07-19-2007

Thanks...I will look this over. Can you explain the "mls qos srr-queue output cos-map queue x threshold x x" command. I don't quite understand these.

Thanks again.

Dan

johnnylingo · ‎07-24-2007

On the 3560, and 3750 there are 4 different output queues. By default, traffic gets assigned the following (CoS -> Queue)

5 -> Q1

0,1 -> Q2

2,3 -> Q3

4,6,7 -> Q4

By default, the 4 Queues will share buffers equally. But with the "priority-queue out" command, Q1 becomes the priority queue and gets preferential treatment compared to the others.

This should prioritize your Voice traffic, assuming it is correctly marked with CoS 5 and/or a DSCP value between 40 and 47. Check the documentation for your VoIP PBX and phones to be sure.

What the "threshold" commands let you do is put different types of traffic in the same queue, but still allow one traffic to be more important than the other. For example:

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

mls qos srr-queue output cos-map queue 4 threshold 3 0

I am putting both CoS 0 and 1 in Queue #4, but 1 gets threshold 2 and 0 gets threshold 3. Threshold 1 and 2 are adjustable, Threshold 3 is not and never gets dropped unless there is no other option.

trptplayer1 · ‎07-24-2007

Thanks,

I will look these over! There is a lot to learn with QoS.