Cisco Nexus 5000 Series Switch CLI Software Configuration Guide (OL-16597-01, July 2009)

CHAPTER 32
Configuring QoS
This chapter describes how to configure quality of service (QoS) on Cisco Nexus 5000 Series switches. It
contains the following sections:
• Information About QoS, page 421
• QoS Configuration Guidelines and Limitations, page 429
• Configuring System Classes, page 429
• Configuring QoS on Interfaces, page 445
• Configuring Priority Flow Control and Link-Level Flow Control, page 447
• Verifying QoS Configuration, page 448
• Example QoS Configurations, page 454
Information About QoS
The configurable Cisco NX-OS QoS features on the Cisco Nexus 5000 Series switch allow you to classify
the network traffic, police and prioritize the traffic flow, and provide congestion avoidance.
The default QoS configuration on the switch provides lossless service for Fibre Channel and Fibre Channel
Over Ethernet (FCoE) traffic and best-effort service for Ethernet traffic. QoS can be configured to provide
additional classes of service for Ethernet traffic. Cisco Nexus 5000 Series QoS features are configured using
Cisco Modular QoS CLI (MQC).
Standard Ethernet is a best-effort medium which means that it lacks any form of flow control. In the event
of congestion or collisions, Ethernet will drop packets. The higher level protocols detect the missing data
and retransmit the dropped packets.
Fibre Channel requires a reliable transport system that guarantees the delivery of every packet. To properly
support FCoE, Ethernet has been enhanced with a priority flow control (PFC) mechanism to prevent
congestion.
Note
Cisco Nexus 5000 Series Switch CLI Software Configuration Guide
OL-16597-01 421