Cisco Nexus 1000V Quality of Service Configuration Guide, Release 4.2(1)SV1(5.2)
Overview
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Overview

Overview

This chapter contains the following sections:

Information About Quality of Service

You can use QoS to provide the most desirable flow of traffic through a network. QoS allows you to classify your network traffic, police and prioritize the traffic flow, and provide congestion avoidance. Traffic is processed based on how you classify it and the QoS policies that you put in place.

You can implement a QoS policy using the following steps:

  1. Define a traffic class by using the class-map command. For more information, see Configuring QoS Classification.
  2. Create a traffic class by using the policy-map command. A traffic policy defines how specific traffic is to be acted upon to improve the quality of service. For more information, see Configuring QoS Marking Policies.
  3. Attach the traffic policy to an interface or port profile by using the service-policy command. For more information, see Creating Ingress and Egress Policies.
  4. Police the traffic. For more information, see Configuring QoS Policing.

Traffic Classification and Marking

You can use traffic classification and marking to sort and modify traffic for the best quality of service (QoS). The following table describes these processes.

Qos Method

Description

Command

Mechanism

Traffic Classifications

Groups network traffic based on defined criteria.

match

class maps

Traffic Marking

Modifies traffic attributes by class.

set

policy maps

QoS Commands

QoS configuration commands are shown in the following table:

Command

Configuration

Description

class-map

Global configuration

Defines a class map that represents a class of traffic.

table-map

Global configuration

Defines a table map that represents a mapping from one set of field values to another set of field values. You can reference a table map from a policy map.

policy-map

Global configuration

Defines a policy map that represents a set of policies to be applied to a set of class maps. Policy maps can reference table maps.

match

Class map QoS configuration

Applies a specified policy map to input or output packets on interfaces configured as follows:

  • inherited from a port-profile
  • port-channel
  • Ethernet
  • vEthernet

set

Policy map QoS configuration

Defines the action to take regarding packet data rates.

service-policy

Interface or port profile configuration

Defines the criteria for a class map.

police

Policy map class QoS configuration

Defines the packet header values for a policy map.

Default QoS Behavior

QoS has no default behavior. Policing and prioritization of traffic are only implemented when you apply a policy map to an interface. The only exception is that, by default, the CoS value for control and packet VLAN traffic is set to 6. This value can be overridden with an explicit QoS policy that is configured on the interface that carries the control and packet VLAN traffic. However, when designing your QoS and ACL policies, note that access control lists (ACLs) that are referenced within a QoS policy are processed as follows as part of the QoS policy:

  • QoS ingress processing follows ACL processing.
  • QoS egress processing precedes ACL egress processing.

Supported RFCs

The following table lists RFCs that are supported by QoS:

Number

Title

RFC 2475

Architecture for Differentiated Services

RFC 2697

A Single Rate Three Color Marker

RFC 2698

A Dual Rate Three Color Marker

RFC 3289

Management Information Base for the Differentiated Services Architecture

RFC 3550

RTP: A Transport Protocol for Real-Time Applications

High Availability Requirements for QoS Features

QoS recovers its previous state after a software restart, and it is able to switch over from the active supervisor to the standby supervisor without a loss of state.

Commonly Used DSCP Values

You can mark both incoming and outgoing packets. The following commonly used DSCP values are described in RFC 2475.

DSCP Value

Decimal Value

Meaning

Drop Probability

Equivalent IP Precedence Values

101 110

46

High Priority Expedited Forwarding (EF)

N/A

101 - Critical

000 000

0

Best effort

N/A

000 - Routine

001 010

10

AF11

Low

001 - Priority

001 100

12

AF12

Medium

001 - Priority

001 110

14

AF13

High

001 - Priority

010 010

18

AF21

Low

001 - immediate

010 100

20

AF22

Medium

001 - immediate

010 110

22

AF23

High

001 - immediate

011 010

26

AF31

Low

011 - Flash

011 100

28

AF32

Medium

011 - Flash

011 119

30

AF33

High

011 - Flash

100 010

34

AF41

Low

100 - Flash Override

100 100

36

AF42

Medium

100 - Flash Override

100 110

38

AF43

High

100 - Flash Override

001 000

8

CS1

 

1

010 000

16

CS2

 

2

011 000

24

CS3

 

3

100 000

32

CS4

 

4

101 000

40

CS5

 

5

110 000

48

CS6

 

6

111 000

56

CS7

 

7

000 000

0

Default

   

101 110

46

EF

   

IP Precedence Values

The precedence values from least to most important are as follows:

Value

Description

000 (0)

Routine or Best Effort

001 (1)

Priority

010 (2)

Immediate

011 (3)

Flash (mainly used for voice signaling or for video)

100 (4)

Flash Override

101 (5)

Critical (mainly used for voice RTP)

110 (6)

Internet

111 (7)

Network

QoS Configuration Limits

The maximum configuration limits for the Cisco Nexus 1000V are as follows:

QoS Features

Maximum Limits

Match criteria per class-map

32

Class-maps per policy map

64

Class-maps per server

64 (with policy holders)

Policy-maps per server

16

Service policies per server

128