Packets with COS tags espaping our COS maps

[lance.elmshaeuser]

Background. 4 switch 3750 stack. Switch #4 is the master.

We have the following QoS cos-maps setup on our switch.

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

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

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

by this definition anything with a COS of 1,2,3,4,6,7 should go into Queue 2 and anything with a COS of 1 should go into queue 3.

The switch uplink is set to trust DSCP. Here are our DSCP to COS maps and COS to DSCP.

Dscp-cos map:

d1 : d2 0 1 2 3 4 5 6 7 8 9

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

0 : 00 00 00 00 00 00 00 00 01 01

1 : 01 01 01 01 01 01 02 02 02 02

2 : 02 02 02 02 03 03 03 03 03 03

3 : 03 03 04 04 04 04 04 04 04 04

4 : 05 05 05 05 05 05 05 05 06 06

5 : 06 06 06 06 06 06 07 07 07 07

6 : 07 07 07 07

Cos-dscp map:

cos: 0 1 2 3 4 5 6 7

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

dscp: 0 8 16 24 32 40 48 56

Somehow we are experiencing drops on Queue 1 however.

switch#remote command 1 show platform port-asic stats drop fastethernet 1/0/24

Switch : 1 :

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

Interface Fa1/0/24 TxQueue Drop Statistics

Queue 0

Weight 0 Frames 0

Weight 1 Frames 0

Weight 2 Frames 0

Queue 1

Weight 0 Frames 547384

Weight 1 Frames 100

Weight 2 Frames 0

Queue 2

Weight 0 Frames 0

Weight 1 Frames 0

Weight 2 Frames 0

Queue 3

Weight 0 Frames 0

Weight 1 Frames 0

Weight 2 Frames 633

This is only incrementing when the user is actively using a video system called XOS. How/Why are packets getting mapped into queue 1 given our cos maps?

[cisco_lad2004]

Lance,

by this definition anything with a COS of 1,2,3,4,6,7 should go into Queue 2 and anything with a COS of 1 should go into queue 3

Your config is actually doing the following:

COS 2,3,4,6 & 7 to Q2

COS 1 to Q2

COS 0 to Q3

If too many packets are queued on Q2, there will be drops.

How is Video traffic marked, COS5 / DSCP 40-47 ?

Sam

[lance.elmshaeuser]

True, true on the cos-map breakdown. Anything with a COS of 2,3,4,6,and 7, should also be dropped at threshold 1 in queueu 2 and anything with COS of 1 should be dropped at threshold 3 in queue 2.

We don't have a cos-map for COS 5. Maybe this is the problem. How can you tell what the default queue is if no cos-map is specified.

[cisco_lad2004]

"sh mls qos maps cos-output-q" will confirm that Q1 is ur priority Q and mapped to COS5.

Typically this Q is policed so it does not starve the other Qs. so one way to validate if this indeed your problem, try remarking Video traffic at edge to another available Q that is not over used.

HTH

Sam