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Catalyst 2960 Switch Software Configuration Guide
OL-8603-04
Chapter 28 Configuring QoS
Configuring Auto-QoS
• Depending on the QoS label assigned to a frame and the mutation chosen, the DSCP and CoS values
of the frame are rewritten. If you do not configure the mutation map and if you configure the port
to trust the DSCP of the incoming frame, the DSCP value in the frame is not changed, but the CoS
is rewritten according to the DSCP-to-CoS map. If you configure the port to trust the CoS of the
incoming frame and it is an IP packet, the CoS value in the frame is not changed, but the DSCP
might be changed according to the CoS-to-DSCP map.
The input mutation causes the DSCP to be rewritten depending on the new value of DSCP chosen.
The set action in a policy map also causes the DSCP to be rewritten.
Configuring Auto-QoS
You can use the auto-QoS feature to simplify the deployment of existing QoS features. Auto-QoS makes
assumptions about the network design, and as a result, the switch can prioritize different traffic flows
and appropriately use the ingress and egress queues instead of using the default QoS behavior. (The
default is that QoS is disabled. The switch then offers best-effort service to each packet, regardless of
the packet contents or size, and sends it from a single queue.)
When you enable auto-QoS, it automatically classifies traffic based on the traffic type and ingress packet
label. The switch uses the resulting classification to choose the appropriate egress queue.
You use auto-QoS commands to identify ports connected to Cisco IP Phones and to devices running the
Cisco SoftPhone application. You also use the commands to identify ports that receive trusted traffic
through an uplink. Auto-QoS then performs these functions:
• Detects the presence or absence of Cisco IP Phones
• Configures QoS classification
• Configures egress queues
These sections contain this configuration information:
• Generated Auto-QoS Configuration, page 28-20
• Effects of Auto-QoS on the Configuration, page 28-24
• Auto-QoS Configuration Guidelines, page 28-25
• Enabling Auto-QoS for VoIP, page 28-25
• Auto-QoS Configuration Example, page 28-27
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