Configuring Auto-Qos - Cisco Catalyst 3750 Software Configuration Manual

Chapter 26 Configuring QoS
LLQ
LLQ provides strict-priority queueing for a traffic class. It enables delay-sensitive data, such as voice,
to be sent before packets in other queues are sent. The priority queue is serviced first until it is empty.
Only one traffic stream can be destined for the priority queue per class-level policy. The priority queue
restricts all traffic streams in the same hierarchy, and you should use care when configuring this feature.
You enable the priority queue for a traffic class by using the priority policy-map class configuration
command at the class level. For configuration information, see the
QoS Policy" section on page
Shaping
Shaping provides a process for delaying out-of-profile packets in queues so that they conform to a
specified profile. Shaping is distinct from policing. Policing drops packets that exceed a configured
threshold, but shaping buffers packets so that traffic remains within a threshold. Shaping offers greater
smoothness in handling traffic than policing. You enable average-rate traffic shaping on a traffic class
by using the shape policy-map class configuration command at the class level or at the VLAN level. At
the physical level of the hierarchy, you can shape only the class-default class by using the shape
policy-map class configuration command in an egress policy attached to an ES port. For configuration
information, see the

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:
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These sections describe how to configure auto-QoS on your switch:
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"Configuring an Egress Hierarchical QoS Policy" section on page
Detects the presence or absence of IP phones
Configures QoS classification
Configures egress queues
Generated Auto-QoS Configuration, page 26-30
Effects of Auto-QoS on the Configuration, page 26-33
Auto-QoS Configuration Guidelines, page 26-33
Enabling Auto-QoS for VoIP, page 26-34
Auto-QoS Configuration Example, page 26-35
"Configuring an Egress Hierarchical
Catalyst 3750 Metro Switch Software Configuration Guide
Configuring Auto-QoS
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