35-35
Catalyst 3750 SwitchSoftware Configuration Guide
OL-8550-09
Chapter35 Configuring QoS
Configuring Standard QoS
Configuring Standard QoS
Before configuring standard QoS, you must have a thorough understanding of these items:
The types of applications used and the traffic patterns on your network.
Traffic characteristics and needs of your network. Is the traffic bursty? Do you need to reserve
bandwidth for voice and video streams?
Bandwidth requirements and speed of the network.
Location of congestion points in the network.
These sections contain this configuration information:
Default Standard QoS Configuration, page35-35
Standard QoS Configuration Guidelines, page35-37
Enabling QoS Globally, page35-40 (required)
Enabling VLAN-Based QoS on Physical Ports, page 35-40 (optional)
Configuring Classification Using Port Trust States, page35-41 (required
Configuring a QoS Policy, page35-47 (required)
Configuring DSCP Maps, page35-67 (optional, unless you need to use the
DSCP-to-DSCP-mutation map or the policed-DSCP map)
Configuring Ingress Queue Characteristics, page35-73 (optional)
Configuring Egress Queue Characteristics, page35-77 (optional)

Default Standard QoS Configuration

QoS is disabled. There is no concept of trusted or untrusted ports because the packets are not modified
(the CoS, DSCP, and IP precedence values in the packet are not changed). Traffic is switched in
pass-through mode (packets are switched without any rewrites and classified as best effort without any
policing).
When QoS is enabled with the mls qos global configuration command and all other QoS settings are at
their defaults, traffic is classified as best effort (the DSCP and CoS value is set to 0) without any policing.
No policy maps are configured. The default port trust state on all ports is untrusted. The default ingress
and egress queue settings are described in the “Default Ingress Queue Configuration” section on
page 35-35 and the “Default Egress Queue Configuration” section on page35-36.

Default Ingress Queue Configuration

Table35-6 shows the default ingress queue configuration when QoS is enabled.
Table35-6 Default Ingress Queue Configuration
Feature Queue 1 Queue 2
Buffer allocation 90 percent 10 percent
Bandwidth allocation 144
Priority queue bandwidth 2010