Catalys mls qos

[jduty]

I am working with learning how a network is currently configured with QoS where I work at. Unfortunately, I have not had any courses in QoS. That being said, I think i have started to understanding how your interpret the Cisco matrices in mapping CoS-DSCP and thresholds/buffers to the queues. We are using 2960X Catalyst series switches. 

• I think we are using the auto configuration of mls qos, but how can I tell? 
• I am slightly confused by how the queues are interpreted though. In one area its referenced as queue 1-4 but then when viewing statistics on a port, it is referenced as queue 0-3. Are these queues lining up and are just referenced by different numbers for some reason? 
• How many queues are there? (It looks like there are 4, but I've read there are
• What is the total system buffer size available when defining how much buffer size each queue can utilize?
• What is the unit of measurement of the buffer sizes? Is it percentage of total buffer size on the system? 
• What is the unit of measurement when defining the thresholds? Is that in percentage? Is it packet count? 

As you see, I am most definitely new to the rodeo of QoS, and I am finding it extremely difficult in finding good documentation on how to interpret configs. 

Thanks for your time,

Josh

[Leonardo Pena Davila]

Hi, 

A good video to understand QoS https://www.youtube.com/watch?v=6UJZBeK_JCs 

Regards

[Joseph W. Doherty]

"I think we are using the auto configuration of mls qos, but how can I tell?"

AutoQoS is a configuration option, i.e. it adds and reconfigures QoS commands.  Look for config statements with "auto" in them.

"In one area its referenced as queue 1-4 but then when viewing statistics on a port, it is referenced as queue 0-3."

Correct, it's very confusing!  There are four queues, sometimes numbered as 0..3 sometimes 1..4.

"How many queues are there? (It looks like there are 4, . . ."

Correct, i.e. there are 4 (per interface).

"What is the total system buffer size available when defining how much buffer size each queue can utilize?"

I recall (?) there's 2 MB for the whole switch.

". . . how much buffer size each queue can utilize?"

Depends on QoS configuration, but I recall (?) computing maximum amount of buffer space one queue can use is something like 83%,

"What is the unit of measurement of the buffer sizes?"

Percentages of percentages.  Very difficult to explain.  There was a 3750 QoS document published within the community that explained how it works - hopefully @leonardo Pena Davila video reference explains it too (I haven't watched that video).

"What is the unit of measurement when defining the thresholds? Is that in percentage? Is it packet count?"

I recall (?) also percentage.

[jduty]

This is extremely helpful. If auto qos is configured, is there a way to view the mappings that are automatically configured? 

From my understanding, the confgs that you see when you do a sh run are custom mappings, correct? 

mls qos map cos-dscp 0 8 16 24 32 46 48 56
mls qos srr-queue output cos-map queue 1 threshold 3 4 5
mls qos srr-queue output cos-map queue 2 threshold 1 2
mls qos srr-queue output cos-map queue 2 threshold 2 3
mls qos srr-queue output cos-map queue 2 threshold 3 6 7
mls qos srr-queue output cos-map queue 3 threshold 3 0
mls qos srr-queue output cos-map queue 4 threshold 3 1
mls qos srr-queue output dscp-map queue 1 threshold 3 32 33 40 41 42 43 44 45
mls qos srr-queue output dscp-map queue 1 threshold 3 46 47
mls qos srr-queue output dscp-map queue 2 threshold 1 16 17 18 19 20 21 22 23
mls qos srr-queue output dscp-map queue 2 threshold 1 26 27 28 29 30 31 34 35
mls qos srr-queue output dscp-map queue 2 threshold 1 36 37 38 39
mls qos srr-queue output dscp-map queue 2 threshold 2 24
mls qos srr-queue output dscp-map queue 2 threshold 3 48 49 50 51 52 53 54 55
mls qos srr-queue output dscp-map queue 2 threshold 3 56 57 58 59 60 61 62 63
mls qos srr-queue output dscp-map queue 3 threshold 3 0 1 2 3 4 5 6 7
mls qos srr-queue output dscp-map queue 4 threshold 1 8 9 11 13 15
mls qos srr-queue output dscp-map queue 4 threshold 2 10 12 14
mls qos queue-set output 1 threshold 1 100 100 50 200
mls qos queue-set output 1 threshold 2 125 125 100 400
mls qos queue-set output 1 threshold 3 100 100 100 400
mls qos queue-set output 1 threshold 4 60 150 50 200
mls qos queue-set output 1 buffers 15 25 40 20

Thanks,

Josh

[Joseph W. Doherty]

"If auto qos is configured, is there a way to view the mappings that are automatically configured?"

Yes and no.  AutoQoS will configure many QoS statements, but by design, it's an "one time" configuration, and those statements can be reconfigured (manually).  Again, some statements might include some indication of being generated, by AutoQoS, by their names, but even those can be (manually) modified.

"From my understanding, the confgs that you see when you do a sh run are custom mappings, correct?"

Generally yes, as defaults, also generally, don't appear.  However, noting what I just described, above, especially on statements that do not include custom naming, you cannot easily tell whether such statements were AutoQoS generated, AutoQoS generated and manually modified, or manually generated from the start.

[jduty]

One more question for you...

Is there is a way to view real time threshold/buffer levels? (Whether through cli or a network monitoring solution)

Thanks,

Josh

[Joseph W. Doherty]

"Is there is a way to view real time threshold/buffer levels?"

As in, how many frames/packets are currently queued?

Hmm, I don't fully recall.  There should be some ASIC commands that will show, up to the moment, drop counts on queues and for their different thresholds.  I recall those stats might also show frames counts that passed through a queue.  But, don't recall any command to show the current number of queue frames/packets.

Generally, but not always, if you can see the stat you want via some command line, it's often available in some OID, via SMTP.