CHAPTER
29-1
Software Configuration Guide—Release 12.2(25)EW
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29
Configuring QoS
This chapter describes how to configure quality of service (QoS) by using automatic QoS (auto-QoS)
commands or by using standard QoS commands on a Catalyst 4500 series switch. It also provides
guidelines, procedures, and configuration examples.
This chapter consists of these sections:
• Overview of QoS, page 29-1
• Configuring Auto-QoS, page 29-16
• Configuring QoS, page 29-22
Note For complete syntax and usage information for the switch commands used in this chapter, refer to the
Catalyst 4500 Series Switch Cisco IOS Command Reference and related publications at
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/index.htm.
Overview of QoS
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 (both unicast and multicast), prioritizes it according to its relative
importance, and uses congestion avoidance to provide priority-indexed treatment; QoS can also limit the
bandwidth used by network traffic. QoS can make network performance more predictable and bandwidth
utilization more effective.
This section contains the following subsections:
• Prioritization, page 29-2
• QoS Terminology, page 29-3
• Basic QoS Model, page 29-5
• Classification, page 29-5
• Policing and Marking, page 29-9
• Mapping Tables, page 29-13
• Queueing and Scheduling, page 29-13
• Packet Modification, page 29-15
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