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You can use quality of service (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:
Define a traffic class by using the class-map command. For more information, see Configuring QoS Classification.
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.
Attach the traffic policy to an interface or port profile by using the service-policy command. For more information, see .
Police the traffic. For more information, see Configuring QoS Policing.
QoS classifies network traffic, uses or assigns QoS labels to indicate priority, makes the packets comply with the configured resource usage limits (polices the traffic and marks the traffic), and provides congestion avoidance where resource contention exists. 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 matching the class. |
set |
policy maps |
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 |
Defines the criteria for a class map. |
set |
Policy map QoS configuration |
Defines the action to be taken on the packet. |
service-policy |
Interface or port profile configuration |
Applies a specified policy map to input or output packets on interfaces configured as follows: |
police |
Policy map class QoS configuration |
Defines the rate at which data traffic is monitored. |
QoS has no default behavior. Policing and prioritization of traffic are implemented only when you apply a policy map to an interface. When you are configuring QoS with an ACL, note that packets are processed as follows:
The following table lists RFCs that are supported by QoS.
Number |
Title |
---|---|
Architecture for Differentiated Services |
|
A Single Rate Three Color Marker |
|
A Dual Rate Three Color Marker |
|
Management Information Base for the Differentiated Services Architecture |
|
RTP: A Transport Protocol for Real-Time Applications |
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.
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 |
010—Immediate |
010 100 |
20 |
AF22 |
Medium |
010—Immediate |
010 110 |
22 |
AF23 |
High |
010—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 |
The IP precedence values from least to most important are listed in the following table.
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 |
The configuration limits are documented in the Cisco Nexus 1000V Resource Availability Reference.