S e n d d o c u m e n t a t i o n c o m m e n t s t o m d s f e e d b a c k - d o c @ c i s c o . c o m
About Control Traffic
The Cisco MDS 9000 Family supports QoS for internally and externally generated control traffic. Within
a switch, control traffic is sourced to the supervisor module and is treated as a high priority frame. A
high priority status provides absolute priority over all other traffic and is assigned in the following cases:
Enabling or Disabling Control Traffic
By default, the QoS feature for certain critical control traffic is enabled. These critical control frames
are assigned the highest (absolute) priority.
We do not recommend disabling this feature as all critical control traffic is automatically assigned the
lowest priority once you issue this command.
To disable the high priority assignment for control traffic, follow these steps:
switch# config t
switch(config)# no qos control priority 0
switch(config)# qos control priority 0
Displaying Control Traffic Information
Use the show qos statistics command to view the current state of the QoS configuration for critical
control traffic. This command displays the current QoS settings along with the number of frames marked
high priority. The count is only for debugging purposes and cannot be configured (see
Example 56-2 Displays Current QoS Settings
switch# show qos statistics
Total number of FC frames transmitted from the Supervisor= 15767
Number of highest-priority FC frames transmitted
Current priority of FC control frames = 0
Cisco MDS 9000 Family CLI Configuration Guide
About Service Policy Enforcement, page 56-9
Applying Service Policies, page 56-9
About the DWRR Traffic Scheduler Queue, page 56-10
Changing the Weight in a DWRR Queue, page 56-10
Displaying Data Traffic Information, page 56-10
Internally generated time-critical control traffic (mostly Class F frames).
Externally generated time-critical control traffic entering a switch in the Cisco MDS 9000 Family
from a another vendor's switch. High priority frames originating from other vendor switches are
marked as high priority as they enter a switch in the Cisco MDS 9000 Family.
Configuring Fabric Congestion Control and QoS
Enters configuration mode.
Enables the control traffic QoS feature.
Disables the control traffic QoS feature.
(0 = lowest; 7 = highest)
OL-16184-01, Cisco MDS SAN-OS Release 3.x