Cisco Catalyst 4500 Series Configuration Manual page 917

Chapter 40 Configuring Quality of Service
The three policy maps are defined as follows:
policy-map AutoQos-VoIP-Input-Dscp-Policy
•
This policy map is applied as an input service policy on an Layer 3 interface (such as an uplink
connection to a neighboring switch) when auto-QoS is configured on the port.
policy-map AutoQos-VoIP-Input-Cos-Policy
•
This policy map is applied as an input service policy on an Layer 2 interface that could be either an
uplink connection or a port hooked to a Cisco IP Phone.
policy-map AutoQos-VoIP-Output-Policy
•
This policy map is applied as an output policy for any port on which auto-QoS is configured,
establishing policy governing egress traffic on the port based on whether it is voice data or control
traffic.
The purpose of the input policy maps is to identify voice data or control traffic and mark it as such as it
traverses the switch. The output policy map matches the packets on the marking occurring on ingress
and then applies egress parameters such as bandwidth, policing and/or priority queuing.
For switch-to-switch connections, the [no] auto qos voip trust command is used to apply an input and
output service policy on the interface:
service-policy input AutoQos-VoIP-Input-Cos-Policy
OR
service-policy input AutoQos-VoIP-Input-Dscp-Policy
AND
service-policy output AutoQos-VoIP-Output-Policy
The selection of the input policy depends on whether the port is Layer 2 or Layer 3. For Layer 2, the
policy trusts the Cos setting in the received packets. For Layer 3 ports, it relies on the DSCP value
contained in the packets.
For phone connected ports, the [no] auto qos voice cisco-phone command is used to apply the following
service policy to the port:
qos trust device cisco-phone
service-policy input AutoQos-VoIP-Input-Cos-Policy
AND
service-policy output AutoQos-VoIP-Output-Policy
It establishes a trusted boundary that recognizes Cisco IP Phones and trusts the Cos setting of the packets
from the phone. If a Cisco IP Phone is not detected, the Cos field is ignored and the packets are not
classified as voice traffic. Upon detecting a Cisco phone, the ingress packets are marked based on the
Cos value in the packets. This marking is used on egress for proper traffic classification and handling.
Auto qos srnd4—Is generated when any new auto qos command is configured on an interface and
migrates from legacy CLIs to generate new configurations. This CLI only generates a global
configuration if during migration, one or more interfaces has legacy auto-QoS enabled
Auto qos video—Generates QoS configuration for untrusted interfaces. It incorporates a service-policy
to classify the traffic coming from untrusted desktops/devices and marks them accordingly.
OL-25340-01
dbl
Software Configuration Guide—Release IOS XE 3.3.0SG and IOS 15.1(1)SG
Configuring Auto-QoS
40-53