Hi
Because this is the default ie. COS value 5 is mapped to the priority queue (assuming the module has one).
If you went onto an interface and did
int gi8/1
priority-queue cos-map 1 3
then it would then show in the running config as
int gi8/1
priority-queue cos-map 1 3 5
because you have changed from the default.
To verify see this example from one of our 6500 switches
SZ-JFH-F00-DTE1#sh queueing int gi8/1
Interface GigabitEthernet8/1 queueing strategy: Weighted Round-Robin
Port QoS is enabled
Trust state: trust DSCP
Extend trust state: not trusted [COS = 0]
Default COS is 0
Queueing Mode In Tx direction: mode-cos
Transmit queues [type = 1p2q2t]:
Queue Id Scheduling Num of thresholds
-----------------------------------------
1 WRR low 2
2 WRR high 2
3 Priority 1 ***** priority queue is mapped to queue 3 *****
WRR bandwidth ratios: 100[queue 1] 255[queue 2]
queue-limit ratios: 70[queue 1] 15[queue 2] 15[Pri Queue]*same as Q2
queue random-detect-min-thresholds
----------------------------------
1 40[1] 70[2]
2 40[1] 70[2]
queue random-detect-max-thresholds
----------------------------------
1 70[1] 100[2]
2 70[1] 100[2]
queue thresh cos-map
---------------------------------------
1 1 0 1
1 2 2 3
2 1 4 6
2 2 7
3 1 5 ***** and here is cos value 5 mapped to queue 3 by default *****
Queueing Mode In Rx direction: mode-cos
Receive queues [type = 1q2t]:
Queue Id Scheduling Num of thresholds
-----------------------------------------
1 Standard 2
queue tail-drop-thresholds
--------------------------
1 100[1] 100[2]
queue thresh cos-map
---------------------------------------
1 1 0 1 2 3 4 5 6 7
SZ-JFH-F00-DTE1#
HTH
Jon
