Ing Filosofia

C H A P T E R

13

Configuring QoS
This chapter describes how to configure quality of service (QoS) on your switch. With this feature, you
can provide preferential treatment to certain types of traffic. Without QoS, the switch offers best-effort
service to each packet, regardless of the packet contents or size. It transmits the packets without any
assurance of reliability, delay bounds,or throughput.
To use the features described in this chapter, you must have the enhanced software image installed on
your switch.
If you have the standard software image installed on your switch, you cannot configure some of the
features. Table 13-1 lists the sections that describe the features that you can configure.
Table 13-1 Sections Describing Standard-Software Features

TopicSection

Queueing and scheduling at
the egress ports

“Queueing and Scheduling” section on page 13-8.

Configuring QoS

“Configuring QoS” section on page 13-9.
“Default QoS Configuration” section on page 13-9.
“Configuring the CoS Value for an Interface” section on
page 13-13.
“Configuring CoS and WRR” section on page 13-23.

Note

For complete syntax and usage information for thecommands used in this chapter, refer to the
Catalyst 2950 Desktop Switch Command Reference for this release.
QoS can be configured either by using the Cluster Management Suite (CMS) or through the
command-line interface (CLI). Refer to the CMS online help for step-by-step configuration procedures
through CMS. For information about accessing and using CMS, see the “Getting Started with CMS”
sectionon page 2-1.

Catalyst 2950 Desktop Switch Software Configuration Guide
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Chapter 13

Configuring QoS

Understanding QoS

You can also use these wizards to configure QoS:

Note

These wizards are available only if your switch is running the enhanced software image.
•

Priority data wizard—Lets you assign priority levels to data applications based on their TCPor UDP
ports. It provides a standard list of applications, and you select the ones that you want to prioritize,
the priority levels, and the interfaces where the prioritization occurs. Refer to the priority data
wizard online help for step-by-step procedures on using this wizard.

•

Video wizard—Gives traffic that originates from specified video servers a higher priority than thepriority of data traffic. The wizard assumes that the video servers are connected to a single device
in the cluster. Refer to the video wizard online help for step-by-step procedures on using this wizard.

This chapter consists of these sections:
•

Understanding QoS, page 13-2

•

Configuring QoS, page 13-9

•

Displaying QoS Information, page 13-25

•

QoS Configuration Examples, page13-25

Understanding QoS
This section describes how QoS is implemented on the Catalyst 2950 switch. If you have the standard
software image installed on your switch, some concepts and features in this section might not apply.
For a list of available features, see Table 13-1 on page 13-1.
Typically, networks operate on a best-effort delivery basis, which means that all traffic has equalpriority
and an equal chance of being delivered in a timely manner. When congestion occurs, all traffic has an
equal chance of being dropped.
When you configure the QoS feature, you can select specific network traffic, prioritize it according to
its relative importance, and use congestion-management and congestion-avoidance techniques to
provide preferential treatment. Implementing QoS in yournetwork makes network performance more
predictable and bandwidth utilization more effective.
The QoS implementation is based on the DiffServ architecture, an emerging standard from the Internet
Engineering Task Force (IETF). This architecture specifies that each packet is classified upon entry into
the network. The classification is carried in the IP packet header, using 6 bits from the...