QoS on 6500

[d.serra]

Hey Guys,

I've been trying to figure out the following configuration and it is starting to make my brian hurt.  Specifically is the 'threshold' value for the 'wrr-queue cos-map' command.  For example, below we see the command 'wrr-queue cos-map 2 6 0 2'.  What does a threashold of 6 mean?  Is it somehow tied to the minimum threasholds of WRED or is it a Tail-Drop-Threashold?  I'm feeling beat on this one so your help is Greatly appreaciated!

interface GigabitEthernet9/43
switchport
switchport access vlan 9
switchport mode access
shutdown
wrr-queue bandwidth 20 40 60
wrr-queue queue-limit 40 25 20
wrr-queue random-detect min-threshold 1 1 1 1 75 1 1 1 1
wrr-queue random-detect min-threshold 2 1 1 1 1 1 50 1 75
wrr-queue random-detect min-threshold 3 1 1 1 1 1 50 1 100
wrr-queue random-detect max-threshold 1 100 100 100 100 100 100 100 100
wrr-queue random-detect max-threshold 2 100 100 100 100 100 75 100 100
wrr-queue random-detect max-threshold 3 100 100 100 100 100 75 100 100
wrr-queue cos-map 1 4 1
wrr-queue cos-map 2 6 0 2
wrr-queue cos-map 2 8 3
wrr-queue cos-map 3 6 4
wrr-queue cos-map 3 8 6 7
no snmp trap link-status
mls qos vlan-based
no cdp enable
spanning-tree guard root

Regards,

Dave

[Jon Marshall]

Dave

Can you post output of -

sh queueing interface gi9/43 | begin queue thresh cos-map

Jon

[d.serra]

I'm sorry but I can't produce any show commands as I do not have access to the equipment.  Just trying to understand the configuration.

[Shashank Singh · Accepted solution]

Hi Dave,

In command, wrr-queue cos-map 2 6 0 2, 2 is the queue-id, 6 is the threshold-id and 0 & 2 are cos values mappped to threshold-is 6 in queue 2 on int gi9/43.

Number of thresholds differ depending on the line card being used. Seeing your configuration it seems that the line card in slot 9 supports 8 threshold values for its queues.

Generally each threshold represents a specific percentage of the queue depth. Let us assume that threshold-id 6 is mapped to 60% of the queue depth. Hence with this configuration, packets marked with cos 0 and 2 will be dropped only after the queue is more than 60% full.

Similarly, wrr-queue cos-map 2 8 3 command maps cos 3 with threshold 8 in queue 2. If we assume that threshold 8 is mapped to 80% of the queue depth, cos 3 packets will not be dropped unless the queue is 80% full and likewise.

These mappings can be seen is show queueing int gi9/43 output.

Let me know if you have any more doubts.

Cheers,

Shashank

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[d.serra]

Thank you Shashank!

Your explanation is very helpful.  Further, it pointed out something else interesting in that drop thresholds are set on CoS values rather then queues.  I used to think that you set WRED min and max values on a per queue basis but from what you have outlined it sounds like queue 2 will start droping CoS 0 and 2 packets at 50% queue depth and CoS 3 at 75% queue depth.  Very very interesting.  Thank you for the clarification.

Dave