Marking Network Traffic

First Published: May 2, 2005
Last Updated: March 2, 2009

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

For the latest feature information and caveats, see 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 for Marking Network Traffic" section.

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

Contents

•Restrictions for Marking Network Traffic

•Information About Marking Network Traffic

•How to Mark Network Traffic

•Configuration Examples for Marking Network Traffic

•Additional References

•Feature Information for Marking Network Traffic

Restrictions for Marking Network Traffic

Traffic marking can be configured on an interface, a subinterface, or an ATM permanent virtual circuit (PVC). Marking network traffic is not supported on the following interfaces:

•ATM switched virtual circuit (SVC)

•Fast EtherChannel

•PRI

•Tunnel

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:

•Cell loss priority (CLP) bit

•CoS value of an outgoing packet

•Discard eligible (DE) bit setting in the address field of a Frame Relay frame

•Discard-class value

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

•MPLS EXP field value in the topmost label on either an input or an 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:

•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 router. The router can use the QoS groups to determine how to prioritize traffic for transmission. The QoS group value is usually 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 Precedence, which have 64 and 8, respectively.

–If changing the Precedence or DSCP value is undesirable.

•If a packet (for instance, in a traffic flow) needs to be marked to differentiate user-defined QoS services is leaving a router and entering a switch, the router 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.

Method for Marking Traffic Attributes

You 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.

Using a set Command

You specify the traffic attribute you want to change with a set command configured in a policy map. Table 1 lists the available set commands and the corresponding attribute. Table 1 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 Commands 1
Traffic Attribute
Network Layer
Protocol

set cos

Layer 2 CoS value of the outgoing traffic

Layer 2

ATM, Frame Relay

set discard-class

discard-class value

Layer 2

ATM, Frame Relay

set dscp

DSCP value in the ToS byte

Layer 3

IP

set fr-de

DE bit setting in the address field of a Frame Relay frame

Layer 2

Frame Relay

set ip tos (route-map)

ToS bits in the header of an IP packet

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


If you are using individual set commands, those set commands are specified in a policy map. The following is a sample of a policy map configured with one of the set commands listed in Table 1.

In this sample configuration, the set cos command has been configured in the policy map (policy1) to mark the set 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 Quality of Service (QoS) Command-Line Interface (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.

For more information about the MQC, see the "Applying QoS Features Using the MQC" module.

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 DSCP value of 3 is grouped into another class. The match criterion is 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.

Table 2 compares the features of traffic classification and traffic marking.

Table 2 Traffic Classification Compared with Traffic Marking

 
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 criterion.

Uses the traffic classes and matching criterion 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 the Cisco IOS release that you are using 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:

Router> enable

Enables privileged EXEC mode.

•Enter your password if prompted.

Step 2 

configure terminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3 

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

Example:

Router(config)# class-map class1

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

•Enter the class map name.

Step 4 

match protocol protocol-name

Example:

Router(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 IOS XE release. See the command documentation for the Cisco IOS XE release that you are using for a complete list of match commands.

Step 5 

end

Example:

Router(config-cmap)# end

(Optional) Returns to privileged EXEC mode.

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

Restrictions

•Before modifying the encapsulation type from IEEE 802.1 Q to ISL, or vice versa, on a subinterface, detach the policy map from the subinterface. After changing the encapsulation type, reattach the 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 router.

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

Note The set cos command is shown in the steps that follow. The set cos command is an example of a set command that can be used when marking traffic. Other set commands can be used. For a list of other set commands, see Table 1.

SUMMARY STEPS

1. enable

2. configure terminal

3. policy-map policy-map-name

4. class {class-name | class-default}

5. set cos cos-value

6. end

7. show policy-map

or

show policy-map policy-map class class-name

8. exit

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

•Enter your password if prompted.

Step 2 

configure terminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3 

policy-map policy-map-name

Example:

Router(config)# policy-map policy1

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

•Enter the policy map name.

Step 4 

class {class-name | class-default}

Example:

Router(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.

•Enter the name of the class or enter the class-default keyword.

Step 5 

set cos cos-value


(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 Table 1.

 
Example:

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

 

Step 6 

end

Example:

Router(config-pmap-c)# end

Returns to privileged EXEC mode.

Step 7 

show policy-map

(Optional) Displays all configured policy maps.

 

or

or

 

show policy-map policy-map class class-name


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

•Enter the policy map name and the class name.

 
Example:

Router# show policy-map

 
 

or

 
 
Example:

Router# show policy-map policy1 class class1

 

Step 8 

exit

Example:

Router# exit

(Optional) Exits privileged EXEC mode.

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

Note Depending on the needs of your network, policy maps can be attached to an interface, a subinterface, or an ATM permanent virtual circuit (PVC).

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

9. exit

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

•Enter your password if prompted.

Step 2 

configure terminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3 

interface type number [name-tag]

Example:

Router(config)# interface serial4/0/0

Configures an interface type and enters interface configuration mode.

•Enter the interface type and number.

Step 4 

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

Example:

Router(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.

•Enter the PVC name, the ATM network virtual path identifier, and the network virtual channel identifier.

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.

Step 5 

exit

Example:

Router(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. If you are not attaching the policy map to an ATM PVC, advance to Step 6.

Step 6 

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

Example:

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

Attaches a policy map to an input or output interface.

•Enter the policy map name.

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

Step 7 

end

Example:

Router(config-if)# end

Returns to privileged EXEC mode.

Step 8 

show policy-map interface type number

Example:

Router# 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.

•Enter the interface type and number.

Step 9 

exit

Example:

Router# exit

(Optional) Exits privileged EXEC mode.

Configuring QoS When Using IPsec VPNs

Note This task is required only if you are using IPsec Virtual Private Networks (VPNs). Otherwise, this task is not necessary. For information about IPsec VPNs, see the "Configuring Security for VPNs with IPsec" module.

Restrictions

This task uses the qos pre-classify command to enable QoS preclassification for the packet. QoS preclassification is not supported for all fragmented packets. If a packet is fragmented, each fragment might received different preclassifications.

SUMMARY STEPS

1. enable

2. configure terminal

3. crypto map map-name seq-num

4. exit

5. interface type number [name-tag]

6. qos pre-classify

7. end

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

•Enter your password if prompted.

Step 2 

configure terminal

Example:

Router# configure terminal

Enters global configuration mode.

Step 3 

crypto map map-name seq-num

Example:

Router(config)# crypto map mymap 10

Enters crypto map configuration mode and creates or modifies a crypto map entry.

•Enter the crypto map name and sequence number.

Step 4 

exit

Example:

Router(config-crypto-map)# exit

Returns to global configuration mode.

Step 5 

interface type number [name-tag]

Example:

Router(config)# interface serial4/0/0

Configures an interface type and enters interface configuration mode.

•Enter the interface type and number.

Step 6 

qos pre-classify

Example:

Router(config-if)# qos pre-classify

Enables QoS preclassification.

Step 7 

end

Example:

Router(config-if)# end

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

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. The traffic with a protocol type of ftp will be put in this class.

Router> enable

Router# configure terminal

Router(config)# class-map class1

Router(config-cmap)# match protocol ftp

Router(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 marking. In this example, a policy map called policy1 has been created, and the set dscp command has been configured for class1. 

Router> enable

Router# configure terminal

Router(config)# policy-map policy1

Router(config-pmap)# class class1

Router(config-pmap-c)# set dscp 2

Router(config-pmap-c)# end

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 of the Serial4/0 interface. 

Router> enable

Router# configure terminal

Router(config)# interface serial4/0/0

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

Router(config-if)# end

Example: Configuring QoS When Using IPsec VPNs

The following is an example of configuring QoS when using IPsec VPNs. In this example, the crypto map command specifies the IPsec crypto map (mymap 10) to which the qos pre-classify command will be applied. 

Router> enable

Router# configure terminal

Router(config)# crypto map mymap 10 

Router(config-crypto-map)# qos pre-classify

Router(config-crypto-map)# exit

Additional References

Related Documents

Related Topic
Document Title

Cisco IOS 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

IPsec and VPNs

"Configuring Security for VPNs with IPsec" module


Standards

Standard
Title

No new or modified standards are supported, and support for existing standards has not been modified.

—


MIBs

MIB
MIBs Link

No new or modified MIBs are supported, and support for existing MIBs has not been modified.

To locate and download MIBs for selected platforms, Cisco IOS XE Software releases, and feature sets, use Cisco MIB Locator found at the following URL:

http://www.cisco.com/go/mibs


RFCs

RFC
Title

No new or modified RFCs are supported, and support for existing RFCs has not been modified.

—


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

Table 3 lists the features in this module.

Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco IOS XE Software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

Note Table 3 lists only the Cisco IOS XE Software release that introduced support for a given feature in a given Cisco IOS XE Software release train. Unless noted otherwise, subsequent releases of that Cisco IOS XE Software release train also support that feature.

Table 3 Feature Information for Marking Network Traffic 

Feature Name
Software Releases
Feature Configuration Information

Class Based Ethernet CoS Matching & Marking (802.1p & ISL CoS)

Cisco IOS XE Release 2.1

This feature was implemented on Cisco ASR 1000 Series Routers.

The following sections provide information about this feature:

•Information About Marking Network Traffic

•How to Mark Network Traffic

Class-Based Marking

Cisco IOS XE Release 2.1

This feature was implemented on Cisco ASR 1000 Series Routers.

The following sections provide information about this feature:

•Information About Marking Network Traffic

•How to Mark Network Traffic

Frame Relay DE Bit Marking

Cisco IOS XE Release  2.1

This feature was implemented on Cisco ASR 1000 Series Routers.

The following sections provide information about this feature:

•Information About Marking Network Traffic

•How to Mark Network Traffic

IP DSCP marking for Frame-Relay PVC

Cisco IOS XE Release 2.1

This feature was implemented on Cisco ASR 1000 Series Routers.

The following sections provide information about this feature:

•Information About Marking Network Traffic

•How to Mark Network Traffic

QoS Group: Match and Set for Classification and Marking

Cisco IOS XE Release 2.1

This feature was implemented on Cisco ASR 1000 Series Routers.

The following sections provide information about this feature:

•Information About Marking Network Traffic

•How to Mark Network Traffic

QoS Packet Marking

Cisco IOS XE Release  2.1

This feature was implemented on Cisco ASR 1000 Series Routers.

The following sections provide information about this feature:

•Information About Marking Network Traffic

•How to Mark Network Traffic

QoS: Traffic Pre-classification

Cisco IOS XE Release 2.1

This feature was introduced on Cisco ASR 1000 Series Routers.

The following sections provide information about this feature:

•Configuring QoS When Using IPsec VPNs

Class-Based Marking

Cisco IOS XE Release 2.2

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

The following sections provide information about this feature:

•Information About Marking Network Traffic

•How to Mark Network Traffic

QoS Packet Marking

Cisco IOS XE Release 2.2

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

The following sections provide information about this feature:

•Information About Marking Network Traffic

•How to Mark Network Traffic


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