Marking Network Traffic

Marking network traffic allows you to set or modify the attributes for traffic (that is, packets) belonging to a specific class or category. When used in conjunction with network traffic classification, marking network traffic is the foundation for enabling many quality of service (QoS) features on your network. This module contains conceptual information and the configuration tasks for marking network traffic.

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.

Prerequisites for Marking Network Traffic

In order to mark network traffic, Cisco Express Forwarding must be configured on both the interface receiving the traffic and the interface sending the traffic.

Restrictions for Marking Network Traffic

Information About Marking Network Traffic

Purpose of Marking Network Traffic

Traffic marking is a method used to identify certain traffic types for unique handling, effectively partitioning network traffic into different categories.

After the network traffic is organized into classes by traffic classification, traffic marking allows you to mark (that is, set or change) a value (attribute) for the traffic belonging to a specific class. For instance, you may want to change the class of service (CoS) value from 2 to 1 in one class, or you may want to change the differentiated services code point (DSCP) value from 3 to 2 in another class. In this module, these values are referred to as attributes.

Attributes that can be set and modified include the following:

  • CoS value of an outgoing packet

  • Discard-class value

  • DSCP value in the type of service (ToS) byte

  • MPLS EXP field value in the topmost label on an input or output interface

  • Multiprotocol Label Switching (MPLS) experimental (EXP) field on all imposed label entries

  • Precedence value in the packet header

  • QoS group identifier (ID)

  • ToS bits in the header of an IP packet

Benefits of Marking Network Traffic

Improved Network Performance

Traffic marking allows you to fine-tune the attributes for traffic on your network. This increased granularity helps single out traffic that requires special handling and, thus, helps to achieve optimal application performance.

Traffic marking allows you to determine how traffic will be treated, based on how the attributes for the network traffic are set. It allows you to segment network traffic into multiple priority levels or classes of service based on those attributes, as follows:

  • The DSCP field (TAG to IP) value does not change in both the uniform mode and in pipe mode. This is applicable to both the Unicast and Multicast traffic scenario.

  • Traffic marking is often used to set the IP precedence or IP DSCP values for traffic entering a network. Networking devices within your network can then use the newly marked IP precedence values to determine how traffic should be treated. For example, voice traffic can be marked with a particular IP precedence or DSCP, and a queueing mechanism can then be configured to put all packets of that mark into a priority queue.

  • Traffic marking can be used to identify traffic for any class-based QoS feature (any feature available in policy-map class configuration mode, although some restrictions exist).

  • Traffic marking can be used to assign traffic to a QoS group within a device. The device can use the QoS groups to determine how to prioritize traffic for transmission. The QoS group value is used for one of the two following reasons:

    • To leverage a large range of traffic classes. The QoS group value has 100 different individual markings, as opposed to DSCP and IP precedence, which have 64 and 8, respectively.

    • If changing the IP precedence or DSCP value is undesirable.

  • If a packet (for instance, in a traffic flow) that needs to be marked to differentiate user-defined QoS services is leaving a device and entering a switch, the device can set the CoS value of the traffic, because the switch can process the Layer 2 CoS header marking. Alternatively, the Layer 2 CoS value of the traffic leaving a switch can be mapped to the Layer 3 IP or MPLS value.

  • Weighted random early detection (WRED) uses precedence values or DSCP values to determine the probability that the traffic will be dropped. Therefore, the Precedence and DSCP can be used along with WRED.

How to Mark Traffic Attributes

You can specify and mark the traffic attribute by using a set command.

With this method, you configure individual set commands for the traffic attribute that you want to mark.

This method is further described in the section that follows.

Mark Traffic Attributes Using a set Command

You specify the traffic attribute that you want to change with a set command configured in a policy map. The table below lists the available set commands and the corresponding attribute. The table also includes the network layer and the network protocol typically associated with the traffic attribute.

Table 1. set Commands and Corresponding Traffic Attribute, Network Layer, and Protocol

set Commands1

Traffic Attribute

Network Layer

Protocol

set cos

Layer 2 CoS value of the outgoing traffic

Layer 2

set discard-class

discard-class value

Layer 2

set dscp

DSCP value in the ToS byte

Layer 3

IP

set mpls experimental imposition

MPLS EXP field on all imposed label entries

Layer 3

MPLS

set mpls experimental topmost

MPLS EXP field value in the topmost label on either an input or an output interface

Layer 3

MPLS

set precedence

Precedence value in the packet header

Layer 3

IP

set qos-group

QoS group ID

Layer 3

IP, MPLS

1 Cisco set commands can vary by release. For more information, see the command documentation for the Cisco release that you are using

Note

The set qos-group can be used for L2 traffic on the Cisco ASR 900 RSP3 Module. 


 policy-map policy1
  class class1
   set dscp 1
   end

Traffic Marking Procedure Flowchart

The figure below illustrates the order of the procedures for configuring traffic marking.

Figure 1. Traffic Marking Procedure Flowchart

Method for Marking Traffic Attributes

You specify and mark the traffic attribute that you want to change by using a set command configured in a policy map.

With this method, you configure individual set commands for the traffic attribute that you want to mark.

Using a set Command

If you are using individual set commands, those set commands are specified in a policy map. The following is a sample policy map configured with one of the set commands listed in the table above. In this sample configuration, the set cos command has been configured in the policy map (policy1) to mark the CoS value. 


 policy-map policy1
  class class1
   set cos 1
   end

For information on configuring a policy map, see the “Creating a Policy Map for Applying a QoS Feature to Network Traffic” section.

The final task is to attach the policy map to the interface. For information on attaching the policy map to the interface, see the “Attaching the Policy Map to an Interface” section.

MQC and Network Traffic Marking

To configure network traffic marking, you use the Modular QoS CLI (MQC).

The MQC is a CLI structure that allows you to complete the following tasks:

  • Specify the matching criteria used to define a traffic class.

  • Create a traffic policy (policy map). The traffic policy defines the QoS policy actions to be taken for each traffic class.

  • Apply the policy actions specified in the policy map to an interface, subinterface, or ATM PVC by using the service-policy command.

Traffic Classification Compared with Traffic Marking

Traffic classification and traffic marking are closely related and can be used together. Traffic marking can be viewed as an additional action, specified in a policy map, to be taken on a traffic class.

Traffic classification allows you to organize into traffic classes on the basis of whether the traffic matches specific criteria. For example, all traffic with a CoS value of 2 is grouped into one class, and traffic with a DSCP value of 3 is grouped into another class. The match criteria are user-defined.

After the traffic is organized into traffic classes, traffic marking allows you to mark (that is, set or change) an attribute for the traffic belonging to that specific class. For instance, you may want to change the CoS value from 2 to 1, or you may want to change the DSCP value from 3 to 2.

The match criteria used by traffic classification are specified by configuring a match command in a class map. The marking action taken by traffic marking is specified by configuring a set command in a policy map. These class maps and policy maps are configured using the MQC.

The table below compares the features of traffic classification and traffic marking.

Table 2. Traffic Classification Compared with Traffic Marking

Feature

Traffic Classification

Traffic Marking

Goal

Groups network traffic into specific traffic classes on the basis of whether the traffic matches the user-defined criterion.

After the network traffic is grouped into traffic classes, modifies the attributes for the traffic in a particular traffic class.

Configuration Mechanism

Uses class maps and policy maps in the MQC.

Uses class maps and policy maps in the MQC.

CLI

In a class map, uses match commands (for example, match cos ) to define the traffic matching criteria.

Uses the traffic classes and matching criteria specified by traffic classification.

In addition, uses set commands (for example, set cos ) in a policy map to modify the attributes for the network traffic.

How to Mark Network Traffic

Creating a Class Map for Marking Network Traffic


Note

The match protocol command is included in the steps below. The match protocol command is just an example of one of the match commands that can be used. See the command documentation for a complete list of match commands.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. class-map class-map-name [match-all | match-any ]
  4. match protocol protocol-name
  5. end

DETAILED STEPS

  Command or Action Purpose
Step 1

enable

Example:


Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal

Enters global configuration mode.

Step 3

class-map class-map-name [match-all | match-any ]

Example:


Device(config)# class-map class1

Creates a class map to be used for matching traffic to a specified class and enters class-map configuration mode.

Step 4

match protocol protocol-name

Example:


Device(config-cmap)# match protocol ftp

(Optional) Configures the match criterion for a class map on the basis of the specified protocol.

Note 

The match protocol command is just an example of one of the match commands that can be used. The match commands vary by Cisco release. See the command documentation for a complete list of match commands.

Step 5

end

Example:


Device(config-cmap)# end

(Optional) Returns to privileged EXEC mode.

Creating a Table Map for Marking Network Traffic


Note

If you are not using a table map, skip this procedure and advance to the “Creating a Policy Map for Applying a QoS Feature to Network Traffic”.

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. table-map table-map-name map from from-value to to-value [default default-action-or-value ]
  4. end

DETAILED STEPS

  Command or Action Purpose
Step 1

enable

Example:


Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal

Enters global configuration mode.

Step 3

table-map table-map-name map from from-value to to-value [default default-action-or-value ]

Example:

Example:


Device(config)# table-map table-map1 map from 2 to 1

Creates a table map using the specified name and enters tablemap configuration mode.

  • Enter the name of the table map you want to create.

  • Enter each value mapping on a separate line. Enter as many separate lines as needed for the values you want to map.

  • The default keyword and default-action-or-value argument set the default value (or action) to be used if a value is not explicitly designated.

Step 4

end

Example:


Device(config-tablemap)#
 
end

(Optional) Exits tablemap configuration mode and returns to privileged EXEC mode.

Creating a Policy Map for Applying a QoS Feature to Network Traffic

Before you begin

The following restrictions apply to creating a QoS policy map:

  • A policy map containing the set qos-group command can only be attached as an input traffic policy. QoS group values are not usable for traffic leaving a device.

  • A policy map containing the set cos command can only be attached as an output traffic policy.

Procedure

Step 1

enable

Example:


Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal

Enters global configuration mode.

Step 3

policy-map policy-map-name

Example:


Device(config)# policy-map policy1

Specifies the name of the policy map and enters policy-map configuration mode.

Step 4

class {class-name | class-default }

Example:


Device(config-pmap)# class class1

Specifies the name of the class whose policy you want to create and enters policy-map class configuration mode. This class is associated with the class map created earlier.

Step 5

set cos cos-value

Example:

Device(config-pmap-c)# set cos 2

(Optional) Sets the CoS value in the type of service (ToS) byte.

Note 

The set cos command is an example of one of the set commands that can be used when marking traffic. Other set commands can be used. For a list of other set commands, see “Information About Marking Network Traffic”.

Step 6

end

Example:


Device(config-pmap-c)# end

Returns to privileged EXEC mode.

Step 7

show policy-map

Example:


Device# show policy-map

(Optional) Displays all configured policy maps.

Step 8

show policy-map policy-map class class-name

Example:


Device# show policy-map policy1 class class1

(Optional) Displays the configuration for the specified class of the specified policy map.

What to Do Next

Create and configure as many policy maps as you need for your network. To create and configure additional policy maps, repeat the steps in the “Creating a Policy Map for Applying a QoS Feature to Network Traffic” section. Then attach the policy maps to the appropriate interface, following the instructions in the “Attaching the Policy Map to an Interface” section.

Attaching the Policy Map to an Interface

SUMMARY STEPS

  1. enable
  2. configure terminal
  3. interface type number [name-tag ]
  4. pvc [name ] vpi / vci [ilmi | qsaal | smds | l2transport ]
  5. exit
  6. service-policy {input | output } policy-map-name
  7. end
  8. show policy-map interface type number

DETAILED STEPS

  Command or Action Purpose
Step 1

enable

Example:


Device> enable

Enables privileged EXEC mode.

  • Enter your password if prompted.

Step 2

configure terminal

Example:


Device# configure terminal

Enters global configuration mode.

Step 3

interface type number [name-tag ]

Example:


Device(config)# interface serial4/0/0

Configures an interface type and enters interface configuration mode.

Step 4

pvc [name ] vpi / vci [ilmi | qsaal | smds | l2transport ]

Example:


Device(config-if)# pvc cisco 0/16

(Optional) Creates or assigns a name to an ATM permanent virtual circuit (PVC), specifies the encapsulation type on an ATM PVC, and enters ATM virtual circuit configuration mode.

Note 

This step is required only if you are attaching the policy map to an ATM PVC. If you are not attaching the policy map to an ATM PVC, advance to Step 6 below.

Step 5

exit

Example:


Device(config-atm-vc)# exit

(Optional) Returns to interface configuration mode.

Note 

This step is required only if you are attaching the policy map to an ATM PVC and you completed Step 4 above. If you are not attaching the policy map to an ATM PVC, advance to Step 6 below.

Step 6

service-policy {input | output } policy-map-name

Example:


Device(config-if)# service-policy input policy1

Attaches a policy map to an input or output interface.

Note 

Policy maps can be configured on ingress or egress devices. They can also be attached in the input or output direction of an interface. The direction (input or output) and the device (ingress or egress) to which the policy map should be attached vary according your network configuration. When using the service-policy command to attach the policy map to an interface, be sure to choose the device and the interface direction that are appropriate for your network configuration.

Step 7

end

Example:


Device(config-if)# end

Returns to privileged EXEC mode.

Step 8

show policy-map interface type number

Example:


Device# show policy-map interface serial4/0/0

(Optional) Displays the traffic statistics of all classes that are configured for all service policies either on the specified interface or subinterface or on a specific PVC on the interface.

Configuration Examples for Marking Network Traffic

Example: Creating a Class Map for Marking Network Traffic

The following is an example of creating a class map to be used for marking network traffic. In this example, a class called class1 has been created. Ttraffic with a protocol type of FTP will be put in this class. 


Device> enable
Device# configure terminal
Device(config)# class-map class1
Device(config-cmap)# match protocol ftp
Device(config-cmap)# end

Example Creating a Policy Map for Applying a QoS Feature to Network Traffic

The following is an example of creating a policy map to be used for traffic classification. In this example, a policy map called policy1 has been created, and the bandwidth command has been configured for class1. The bandwidth command configures the QoS feature CBWFQ. 


Router> enable
Router# configure terminal
Router(config)# policy-map policy1
Router(config-pmap)# class class1
Router(config-pmap-c)# bandwidth percent 50 
Router(config-pmap-c)# end
Router# 
show policy-map policy1 class class1
Router# exit

Note

This example uses the bandwidth command. The bandwidth command configures the QoS feature class-based weighted fair queuing (CBWFQ). CBWFQ is just an example of a QoS feature that can be configured. Use the appropriate command for the QoS feature that you want to use.

Example: Attaching the Policy Map to an Interface

The following is an example of attaching the policy map to the interface. In this example, the policy map called policy1 has been attached in the input direction to the Ethernet interface 0. 


Device> enable
Device# configure terminal
Device(config)# interface ethernet 0
Device(config-if)# service-policy input policy1 
Device(config-if)# end

Additional References for Marking Network Traffic

Related Documents

Related Topic

Document Title

Cisco commands

Cisco IOS Master Commands List, All Releases

QoS commands: complete command syntax, command modes, command history, defaults, usage guidelines, and examples

Cisco IOS Quality of Service Solutions Command Reference

MQC

“Applying QoS Features Using the MQC” module

Classifying network traffic

“Classifying Network Traffic” module

Technical Assistance

Description

Link

The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password.

http://www.cisco.com/cisco/web/support/index.html

Feature Information for Marking Network Traffic

The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Table 3. Feature Information for Marking Network Traffic

Feature Name

Software Releases

Feature Configuration Information

Class-Based Marking

Cisco IOS XE Release 2.1

Cisco IOS XE Release 2.2

Cisco IOS XE Release 3.2SE

The Class-Based Packet Marking feature provides a user-friendly command-line interface (CLI) for efficient packet marking by which users can differentiate packets.

This feature was implemented on Cisco ASR 1000 Series Routers.

This feature was integrated into Cisco IOS XE Release 2.2.

Enhanced Packet Marking

Cisco IOS XE Release 3.9S

Cisco IOS XE Release 3.14S

The Enhanced Packet Marking feature allows you to map and convert the marking of a packet from one value to another by using a kind of conversion chart called a table map. The table map establishes an equivalency from one value to another. For example, the table map can map and convert the class of service (CoS) value of a packet to the precedence value of the packet. This value mapping can be propagated for use on the network, as needed.

In Cisco IOS XE Release 3.9S, support was added for the Cisco CSR 1000V Series Routers

In Cisco IOS XE Release 3.14S, support was added for the Cisco 4000 Series Integrated Services Routers.

QoS Packet Marking

Cisco IOS XE Release 2.1

Cisco IOS XE Release 2.2

Cisco IOS XE Release 3.5S

Cisco IOS XE Release 3.9S

Cisco IOS XE Release 3.14S

The QoS Packet Marking feature allows you to mark packets by setting the IP precedence bit or the IP differentiated services code point (DSCP) in the Type of Service (ToS) byte, and to associate a local QoS group value with a packet.

This feature was implemented on Cisco ASR 1000 Series Routers.

This feature was integrated into Cisco IOS XE Software Release 2.2.

In Cisco IOS XE Release 3.5S, support was added for the Cisco ASR 903 Router.

In Cisco IOS XE Release 3.9S, support was added for the Cisco CSR 1000V Series Routers.

In Cisco IOS XE Release 3.14S, support was added for the Cisco 4000 Series Integrated Services Routers.

IP DSCP marking for Frame-Relay PVC

Cisco IOS XE Release 2.1

This feature was implemented on Cisco ASR 1000 Series Routers.

PXF Based Frame Relay DE Bit Marking

12.2(31)SB2

15.0(1)S

PXF Based Frame Relay DE Bit Marking was integrated into the Cisco IOS Release 15.0(1)S release.