Cisco 4500M

29-17
Software Configuration Guide—Release 12.2(25)EW
OL-6696-01
Chapter 29 Configuring QoS
Configuring Auto-QoS
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.
• To take advantage of the auto-QoS defaults, do not configure any standard-QoS commands before
entering the auto-QoS commands. If necessary, you can fine-tune the QoS configuration, but we
recommend that you do so only after the auto-QoS configuration is completed.
• You can enable auto-QoS on static, dynamic-access, voice VLAN access, and trunk ports.
• By default, the CDP is enabled on all interfaces. For auto-QoS to function properly, do not disable
the CDP.
• To enable auto qos voip trust on Layer 3 interfaces, change the port to Layer 3, then apply auto-QoS
to make it trust DSCP.
Table 29-2 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