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27-18
Software Configuration Guide—Release 12.2(25)SG
OL-7659-03
Chapter 27 Configuring Quality of Service
Configuring Auto-QoS
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 27-26.
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 27-2 to the interface.
Effects of Auto-QoS on the Configuration
When auto-QoS is enabled, the auto qos voip interface configuration command and the generated
configuration are added to the running configuration.
Configuration Guidelines
Before configuring auto-QoS, you should be aware of this information:
• In this release, auto-QoS configures the switch only for VoIP with Cisco IP phones.
Table 27-2 Generated Auto-QoS Configuration
Description Automatically Generated Command
The switch automatically enables standard QoS and DBL
configures the cos-to-DSCP map (maps CoS values in
incoming packets to a DSCP value).
Switch(config)# qos
Switch(config)# qos map cos 3 to 26
Switch(config)# qos dbl
Switch(config)# qos map cos 5 to 46
The switch automatically configures the DSCP-to-Tx-queue
mapping.
Switch(config)# qos map dscp 24 25 26 27 b28 29 30
31 to tx-queue 4
Switch(config)# qos map dscp 32 33 34 35 36 37 38 39
to tx-queue 4
The switch automatically sets the ingress classification on the
interface to trust the CoS/DSCP value received in the packet.
Switch(config-if)# qos trust cos
or
Switch(config-if)# qos trust dscp
The switch automatically creates a QoS service policy, enables
DBL on the policy, and attaches it to the interface.
Switch(config)# policy-map autoqos-voip-policy
Switch(config-pmap)# class class-default
Switch(config-pmap-c)# dbl
If you entered the auto qos voip cisco-phone command, the
switch automatically enables the trusted boundary feature,
which uses the CDP to detect the presence or absence of a
Cisco IP phone.
Switch(config-if)# qos trust device cisco-phone
The switch assigns a higher priority for queue 3. Limit for
shaping on queue 3 is selected so that it is 33 percent of the link
speed. Configure shaping as 33 percent on those ports where
sharing is supported.
This procedure ensures that the higher-priority queue does not
starve other queues.
Switch(config-if)# tx-queue 3
Switch(config-if-tx-queue)# priority high
Switch(config-if-tx-queue)# shape percent 33
Switch(config-if-tx-queue)# bandwidth percent 33