Specifications

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Catalyst 2970 Switch Software Configuration Guide
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Chapter 27 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
interface 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 interface 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 identify ports that
receive trusted voice over IP (VoIP) 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 describe how to configure auto-QoS on your switch:
• Generated Auto-QoS Configuration, page 27-18
• Effects of Auto-QoS on the Configuration, page 27-22
• Auto-QoS Configuration Guidelines, page 27-22
• Enabling Auto-QoS for VoIP, page 27-23
• Auto-QoS Configuration Example, page 27-24
Generated Auto-QoS Configuration
By default, auto-QoS is disabled on all interfaces.
When auto-QoS is enabled, it uses the ingress packet label to categorize traffic, to assign packet labels,
and to configure the ingress and egress queues as shown in Table 27-2.
Table 27-2 Traffic Types, Ingress Packet Labels, Assigned Packet Labels, and Queues
VoIP Data
Traffic
VoIP Control
Traffic
Routing Protocol
Traffic
STP BPDU
Traffic All Other Traffic
Ingress DSCP 46 26 – – –
Ingress CoS 5 3 6 7 –
DiffServ EF AF31 – – –