QoS explanation

Brent Rockburn · ‎05-06-2009

Can someone quickly step me through this?

mls qos map dscp-cos 46 47 to 6

mls qos map cos-dscp 0 8 16 24 32 40 46 56

mls qos srr-queue input buffers 35 65

mls qos srr-queue input priority-queue 2 bandwidth 35

mls qos srr-queue input cos-map queue 1 threshold 1 5

mls qos srr-queue input cos-map queue 2 threshold 1 6

mls qos srr-queue output cos-map queue 1 threshold 1 6

mls qos srr-queue output cos-map queue 4 threshold 1 5

mls qos queue-set output 1 threshold 2 100 100 50 400

mls qos queue-set output 1 buffers 40 20 20 20

mls qos

Thanks,

Brent

dgalati000 · ‎05-06-2009

Brent, I can't explain all of it quickly and easily. Until someone can, why don't you try using the TAC website, output interpreter tool. You will have to enter the entire cmd you used to generate this output + this output (into the tool),,and if the tool likes what you put in, you will get an explanation. Here's the url

http://www.cisco.com/en/US/customer/support/index.html

all the way down, middle of the page.

aacole · ‎05-22-2009

Hi Brent,

I've just been reading up 6500 QoS, trying to figure out some of these commands. I think your using a 3560 or 3750 here, and your missing a queue-set 1 and priority-queue out command off your interface?

I can explain some of this:

mls qos map dscp-cos 46 47 to 6 This maps DSCP values 46&47 to CoS 6.

mls qos map cos-dscp 0 8 16 24 32 40 46 56

The values listed are DSCP values assigned to each CoS value, the cos is not shown but the values are from 0 to 7. So DSCP 46 is assigned to cos 6, DSCP 8 is mapped to cos 8 and so on.

The mls input commands I've never used.

mls qos srr-queue output cos-map queue 1 threshold 1 6

This maps the cos value 6 to queue 1, threshold 1.

mls qos srr-queue output cos-map queue 4 threshold 1 5

This maps the cos value 5 to queue 4, threshold 1.

mls qos queue-set output

These commands set the availability of buffers, as a percentage of the queues allocated memory.

mls qos queue-set output 1 buffers 40 20 20 20

This allocates 40% of queue 1 buffer space to queue set 1, and 20% of buffer space from queue 2,3 and 4 to queue-set 1.

So your switch matches packets with DSCP 46 and 47, maps these to cos 6, these packets go into queue 1, which has an amount of memeory alloacted.

If the missing commands are there, queue 1 is defined as the priority queue, any packets in this queue get transmitted ahead of any other packets in other queues.