C H A P T E R
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Catalyst 4500 Series, Catalyst 2948G, Catalyst 2948G-GE-TX, and Catalyst 2980G Switches Software Configuration Guide—Release 8.2GLX
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14
Configuring QoS
This chapter describes how to configure quality of service (QoS) on Catalyst enterprise LAN switches.
Note
For complete syntax and usage information for the commands that are used in this chapter, refer to the
Catalyst 4500 Series, Catalyst 2948G, Catalyst 2948G-GE-TX, and Catalyst 2980G Switches Command
Reference.
This chapter consists of these sections:
•
Understanding How QoS Works, page 14-1
•
Software Requirements, page 14-4
•
QoS Default Configuration, page 14-4
•
Configuring QoS on the Switch, page 14-4
Understanding How QoS Works
These sections describe how QoS works:
•
QoS Overview, page 14-1
•
Understanding QoS Terminology, page 14-2
•
Understanding Classification and Marking at the Ingress Port, page 14-3
•
Understanding Scheduling, page 14-3
QoS Overview
Typically, networks operate on a best-effort delivery basis, which means that all traffic has equal priority
and an equal chance of being delivered in a timely manner. When congestion occurs, all traffic has an
equal chance of being dropped.
QoS selects network traffic, prioritizes it according to its relative importance, and provides
priority-indexed treatment through congestion-avoidance techniques. Implementing QoS in your
network makes network performance more predictable and bandwidth utilization more effective.
QoS classifies traffic by assigning priority-indexed 802.1p class of service (CoS) values to frames at
ingress ports. If traffic is tagged with a CoS value at the ingress port, the switch forwards the value. If
traffic is native, then the switch can rewrite the CoS tag.