Cisco 4500M User Manual

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Software Configuration Guide—Release 12.2(25)EW
OL-6696-01
Chapter 29 Configuring QoS
Configuring Auto-QoS
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 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
content or size, and sends it from a single queue.)
When you enable auto-QoS, it automatically classifies traffic based on 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 IP phones
• Configures QoS classification
• Configures egress queues
These sections describe how to configure auto-QoS on your switch:
• Generated Auto-QoS Configuration, page 29-16
• Effects of Auto-QoS on the Configuration, page 29-17
• Configuration Guidelines, page 29-17
• Enabling Auto-QoS for VoIP, page 29-18
Generated Auto-QoS Configuration
By default, auto-QoS is disabled on all interfaces.
When you enable the auto-QoS feature on the first interface, these automatic actions occur:
• QoS is globally enabled (qos global configuration command).
• DBL is enabled globally (qos dbl global configuration command)
• When you enter the auto qos voip trust interface configuration command, the ingress classification
on the specified interface is set to trust the CoS label received in the packet if the specified interface
is configured as Layer 2 (and is set to trust DSCP if the interface is configured as Layer 3). (See
Table 29-2.)
• When you enter the auto qos voip cisco-phone interface configuration command, the trusted
boundary feature is enabled. It uses the Cisco Discovery Protocol (CDP) to detect the presence or
absence of a Cisco IP phone. When a Cisco IP phone is detected, the ingress classification on the
interface is set to trust the cos label received in the packet, if the interface is configured as Layer 2.
(The classification is set to trust DSCP if the interface is configured as Layer 3.) When a Cisco IP
phone is absent, the ingress classification is set to not trust the cos label in the packet.
For information about the trusted boundary feature, see the “Configuring a Trusted Boundary to
Ensure Port Security” section on page 29-24.
When you enable auto-QoS by using the auto qos voip cisco-phone or the auto qos voip trust interface
configuration commands, the switch automatically generates a QoS configuration based on the traffic
type and ingress packet label and applies the commands listed in Table 29-2 to the interface.

Cisco 4500M Specifications

General

Brand	Cisco
Model	4500M
Category	Network Router
Language	English