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BECN and FECN Marking for Frame Relay over MPLS

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BECN and FECN Marking for Frame Relay over MPLS

Table Of Contents

BECN and FECN Marking for Frame Relay over MPLS

Contents

Prerequisites for BECN and FECN Marking for Frame Relay over MPLS

Restrictions for BECN and FECN Marking for Frame Relay over MPLS

Information About BECN and FECN Marking for Frame Relay over MPLS

How to Configure BECN and FECN Marking for Frame Relay over MPLS

Configuring BECN and FECN Marking at the Class Level

Configuring BECN and FECN Marking at the Interface Level

Verifying the Configuration

Configuration Examples for BECN and FECN Marking for Frame Relay over MPLS

Additional References

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Command Reference

frame-relay congestion-management

set fr-fecn-becn

threshold ecn


BECN and FECN Marking for Frame Relay over MPLS


First Published: August 26, 2003
Last Updated: February, 2006

This feature explains how to configure backward explicit congestion notification (BECN) and forward explicit congestion notification (FECN) bits on packets for Frame Relay over MPLS.

History for the BECN and FECN Marking for Frame Relay over MPLS Feature

Release
Modification

12.0(26)S

This feature was introduced on the Cisco 7200 and 7500 series routers.

12.2(28)SB

This feature was integrated into Cisco IOS Release 12.2(28)SB.


Finding Support Information for Platforms and Cisco IOS Software Images

Use Cisco Feature Navigator to find information about platform support and Cisco IOS software image support. Access Cisco Feature Navigator at http://www.cisco.com/go/fn. You must have an account on Cisco.com. If you do not have an account or have forgotten your username or password, click Cancel at the login dialog box and follow the instructions that appear.

Contents

Prerequisites for BECN and FECN Marking for Frame Relay over MPLS

Restrictions for BECN and FECN Marking for Frame Relay over MPLS

Information About BECN and FECN Marking for Frame Relay over MPLS

How to Configure BECN and FECN Marking for Frame Relay over MPLS

Configuration Examples for BECN and FECN Marking for Frame Relay over MPLS

Additional References

Command Reference

Prerequisites for BECN and FECN Marking for Frame Relay over MPLS

The following prerequisites apply to the Cisco 7500 series router:

Enable distributed IP CEF globally.

Use VIP modules for both ingress and egress interfaces.

Restrictions for BECN and FECN Marking for Frame Relay over MPLS

FECN and BECN marking does not work with L2VPN Interworking. FECN and BECN marking works only with Frame Relay over MPLS in like-to-like configurations.

FECN and BECN marking does not work with Frame Relay over MPLS with port-to-port connections.

If you configure the ECN thresholds at the interface level and also configure shaping, unpredictable behavior can occur. The software cannot differentiate between packets that are shaped and packets that experienced interface congestion.

If you configure ECN thresholds at both the interface level and the class level, only the class-level ECN threshold is used.

If you do not configure ECN thresholds at the class level, the software inherits the interface-level ECN threshold.

You cannot configure priority or bandwidth after configuring the class ECN threshold. If you attempt to configure priority or bandwidth when ECN thresholds have been configured, you receive the following error:

Please remove set fr-fecn-becn from this class first

Information About BECN and FECN Marking for Frame Relay over MPLS

This feature provides congestion management on a provider edge (PE) router's egress interface when Frame Relay traffic is being tunneled across an MPLS cloud. When the congestion queue thresholds configured at the interface or class level of the PE router are exceeded, PE router does the following:

Sets the FECN bit to 1 on the outgoing packets.

Sets the BECN bit to 1 for all traffic destined for the originating CE router, which decreases its traffic based on the number of BECN packets it received.

You can configure FECN and BECN marking at the class level with the set fr-fecn-becn command. You can set up FECN and BECN marking at the interface level with the threshold ecn command.

How to Configure BECN and FECN Marking for Frame Relay over MPLS

You can configure BECN and FECN marking at either the class level or the interface level. This section shows both methods and includes the following sections:

Configuring BECN and FECN Marking at the Class Level (Optional)

Configuring BECN and FECN Marking at the Interface Level (Optional)

Verifying the Configuration (Optional)

Configuring BECN and FECN Marking at the Class Level

Use the following steps to enable BECN and FECN marking at the class level, using the set fr-fecn-becn command.

SUMMARY STEPS

1. enable

2. configure terminal

3. class-map class-map-name

4. match fr-dlci dlci-number

5. exit

6. policy-map policy-map-name

7. class class-name

8. priority {kbps | percent percent} [bytes]

9. set fr-fecn-becn percent

10. exit

11. interface type number

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

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

Example:

Router (config)# class-map dcli-100

Specifies the name of the class map to be created and enters class-map configuration mode.

Step 4 

match fr-dlci dlci-number

Example:

Router(config-cmap)# match fr-dlci 100

(Optional) Configures the class map created above to match traffic based on the Frame Relay DLCI number associated with the packet.

Step 5 

exit

Example:

Router(config-cmap)# exit

Exits class-map configuration mode.

Step 6 

policy-map policy-map-name

Example:

Router(config)# policy-map output-policy

Specifies the name of the traffic policy to configure. Names can be a maximum of 40 alphanumeric characters.

Step 7 

class class-name
Example:
(config-pmap)# class dlci-100

Specifies the name of a predefined traffic class, which was configured with the class-map command, used to classify traffic to the traffic policy.

Step 8 

priority {kbps | percent percent} [bytes]

Example:

Router(config-pmap-c)# priority 250

(Optional) Specifies the guaranteed allowed bandwidth, in kbps or percentage, for priority (time-sensitive) traffic. The optional bytes argument controls the size of the burst allowed to pass through the system without being considered in excess of the configured kbps rate.

Step 9 

set fr-fecn-becn percent

Example:

Router(config-pmap-c)# set fr-fecn-becn 30

Specifies the allowed maximum class queue size, in percentage. If the class queue depth matches or exceeds the percentage, the software initiates BECN and FECN marking.

Step 10 

exit

Example:

Router(config-pmap-c)# exit

Exits policy-map configuration mode.

Step 11 

interface type number

Example:

Router(config-if)# interface s4/0

Configures an interface (or subinterface) type and enters interface configuration mode.

Step 12 

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

Example:

Router(config-if)# service-policy output output-policy

Specifies the name of the policy map to be attached to the input or output direction of the interface.

Configuring BECN and FECN Marking at the Interface Level

Use the following steps to enable BECN and FECN marking at the class level, using the threshold ecn command.

SUMMARY STEPS

1. enable

2. configure terminal

3. class-map class-map-name

4. match fr-dlci dlci-number

5. exit

6. policy-map policy-map-name

7. class class-name

8. priority {kbps | percent percent} [bytes]

9. exit

10. interface type number

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

12. frame-relay congestion-management

13. threshold ecn percentage

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

Example:

Router (config)# class-map dcli-100

Specifies the name of the class map to be created and enters class-map configuration mode.

Step 4 

match fr-dlci dlci-number

Example:

Router(config-cmap)# match fr-dlci 100

(Optional) Configures the class map created above to match traffic based on the Frame Relay DLCI number associated with the packet.

Step 5 

exit

Example:

Router(config-cmap)# exit

Exits class-map configuration mode.

Step 6 

policy-map policy-map-name

Example:

Router(config)# policy-map output-policy

Specifies the name of the traffic policy to configure. Names can be a maximum of 40 alphanumeric characters.

Step 7 

class class-name

Example:

Router(config-pmap)# class dlci-100

Specifies the name of a predefined traffic class, which was configured with the class-map command, used to classify traffic to the traffic policy.

Step 8 

priority {kbps | percent percent} [bytes]

Example:

Router(config-pmap-c)# priority 250

(Optional) Specifies the guaranteed allowed bandwidth, in kbps or percentage, for priority (time-sensitive) traffic. The optional bytes argument controls the size of the burst allowed to pass through the system without being considered in excess of the configured kbps rate.

Step 9 

exit

Example:

Router(config-pmap-c)# exit

Exits policy-map configuration mode.

Step 10 

interface type number

Example:

Router(config-if)# interface s4/0

Configures an interface (or subinterface) type and enters interface configuration mode.

Step 11 

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

Example:

Router(config-if)# service-policy output output-policy

Specifies the name of the policy map to be attached to the input or output direction of the interface.

Step 12 

frame-relay congestion-management

Example:

Router(config-if)# frame-relay congestion-management

Enables Frame Relay congestion management on all switched PVCs on an interface and enters Frame Relay congestion management configuration mode.

Step 13 

threshold ecn percentage

Example:

Router(config-fr-congest)# threshold ecn 50

Configures the threshold at which ECN bits will be set on packets in switched PVCs on the output interface.

Verifying the Configuration

To verify Frame Relay congestion management on switched PVCs, use the following commands:

To displays statistics about PVCs for Frame Relay interfaces, issue the show frame-relay pvc command:

Router# show frame-relay pvc [interface interface] [dlci]

To display information about the configuration and queue at the interface, issue the show interfaces command:

Router# show interfaces type number

For the Cisco 7200 series routers, you can issue the show hqf interface command to show the queue size for interface and class. For the Cisco 7500 series routers, log on to VIP slot and issue show vip hqf command. For the marking to start, the queue size has to be greater than the aggregate limit multiplied by the threshold ECN percentage.

Router # show hqf interface s2/1

Interface Number 7 (type 53) Serial2/1
blt (0x61DDB97C, index 0, fast_if_number 8) layer PHYSICAL
scheduling policy: WFQ
classification policy: CLASS_BASED
drop policy: TAIL
blt flags: 0x0    scheduler: 0x61E9377C

txcount 1532432 drops 0 qdrops 0 nobuffers 0 flowdrops 0
qsize 0 qsize_bytes 0 aggregate limit 918 availbuffers 918 weight 1 perc 0.00
visible_bw 10000000 allocated_bw 10000000 vc_encap 0 ecn_threshold 91
quantum 1500 credit 0 backpressure_policy 1 scheduler_flags 3F
calQ[A]->last_sortq 75, calQ[B]->last_sortq 0, leaf_blt 0x61E9372C

next layer HQFLAYER_CLASS_HIER0 (max entries 256)

blt (0x61DDB918, index 0, fast_if_number 8) layer CLASS_HIER0
scheduling policy: FIFO
classification policy: NONE
drop policy: TAIL
blt flags: 0x0    scheduler: 0x61E9372C
txcount 1532432 drops 0 qdrops 0 nobuffers 0 flowdrops 0
qsize 0 qsize_bytes 0 aggregate limit 918 availbuffers 918 weight 1 perc 0.00
visible_bw 10000000 allocated_bw 10000000 vc_encap 0 ecn_threshold 91
quantum 1500 credit 0 backpressure_policy 1 scheduler_flags 3F
calQ[A]->last_sortq 75, calQ[B]->last_sortq 0, leaf_blt 0x61E9372C

Configuration Examples for BECN and FECN Marking for Frame Relay over MPLS

Table 1 shows two examples of FECN and BECN marking; one at the class level, the other at the interface level.

Table 1 FECN and BECN Marking at the Class Level and Interface Level Configuration Examples

Class Level
Interface Level

class-map match-all dlci-100

match fr-dlci 100

!

policy-map output-policy

    class dlci-100

      bandwidth 250

      queue-limit 10

      set fr-fecn-becn 30

!

interface Serial2/1

    service-policy output output-policy

class-map match-all dlci-100

    match fr-dlci 100

!

policy-map output-policy

    class dlci-100

      bandwidth 250

!

interface Serial2/1

    bandwidth 50000

    service-policy output output-policy

    frame-relay congestion-management

    threshold ecn 50


Additional References

The following sections provide references related to the BECN and FECN Marking for Frame Relay over MPLS feature.

Related Documents

Related Topic
Document Title

Frame Relay over MPLS

Any Transport over MPLS


Standards

Standard
Title

None


MIBs

MIB
MIBs Link

None

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

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


RFCs

RFC
Title

None


Technical Assistance

Description
Link

The Cisco Technical Support & Documentation website contains thousands of pages of searchable technical content, including links to products, technologies, solutions, technical tips, and tools. Registered Cisco.com users can log in from this page to access even more content.

http://www.cisco.com/techsupport


Command Reference

This section documents modified commands only.

frame-relay congestion-management

set fr-fecn-becn

threshold ecn

frame-relay congestion-management

To enable Frame Relay congestion management functions on all switched permanent virtual circuits (PVCs) on an interface, and to enter Frame Relay congestion management configuration mode, use the frame-relay congestion-management command in interface configuration mode. To disable Frame Relay congestion management, use the no form of this command.

frame-relay congestion-management

no frame-relay congestion-management

Syntax Description

This command has no arguments or keywords.

Defaults

Frame Relay congestion management is not enabled on switched PVCs.

Command Modes

Interface configuration

Command History

Release
Modification

12.1(2)T

This command was introduced.

12.0(26)S

This command was integrated into Cisco IOS Release 12.0(26)S.

12.2(27)SXA

This command was integrated into Cisco IOS Release 12.2(27)SXA.

12.2(28)SB

This command was integrated into Cisco IOS Release 12.2(28)SB.


Usage Guidelines

You must enable Frame Relay switching, using the frame-relay switching global command, before you can configure Frame Relay congestion management.

Frame Relay congestion management is supported only when the interface is configured with class-based weighted fair queuing (WFQ).

Examples

In the following example, the frame-relay congestion-management command enables Frame Relay congestion management on serial interface 1. The command also enters Frame Relay congestion management configuration mode so that congestion threshold parameters can be configured.

interface serial1
 encapsulation frame-relay
 frame-relay intf-type dce
 frame-relay congestion-management
  threshold ecn be 0
  threshold ecn bc 20

Related Commands

Command
Description

threshold ecn

Configures the threshold at which ECN bits are set on packets in switched PVCs on the output interface.


set fr-fecn-becn

To enable forward explicit congestion notification (FECN) and backward explicit congestion notification (BECN) with Frame Relay over MPLS, use the set fr-fecn-becn command in policy map class configuration mode. To disable the configuration notification, use the no form of this command.

set fr-fecn-becn percent

no set fr-fecn-becn percent

Syntax Description

percent

Specifies how much (percentage) of the total queue size should be used before marking the FECN and BECN bits. The valid range of percentages is 0 to 99. Setting the threshold to 0 indicates that all traffic is marked with FECN and BECN bits.


Defaults

Frame Relay does not perform FECN and BECN marking.

Command Modes

Policy map class configuration

Command History

Release
Modification

12.0(26)S

This command was introduced.

12.2(27)SXA

This command was integrated into Cisco IOS Release 12.2(27)SXA.

12.2(28)SB

This command was integrated into Cisco IOS Release 12.2(28)SB.


Usage Guidelines

This command works only with Frame Relay over MPLS.

If you configure FECN and BECN bit marking, you cannot configure bandwidth or priority.

Examples

The following example enables marking the FECN and BECN bits when 20 percent of the queue is used:

Router(config)# policy-map policy1 
Router(config-pmap)# class class1
Router(config-pmap-c)# shape 80000
Router(config-pmap-c)# set fr-fecn-becn 20

Related Commands

Command
Description

threshold ecn

Sets the FECN and BECN marking at the interface level.


threshold ecn

To configure the threshold at which explicit congestion notification (ECN) bits will be set on packets in switched permanent virtual circuits (PVCs) on the output interface, use the threshold ecn command in Frame Relay congestion management configuration mode. To remove the threshold configuration, use the no form of this command.

For Frame Relay Switching

threshold ecn {bc | be} percentage

no threshold ecn {bc | be} percentage

For Frame Relay over MPLS

threshold ecn percentage

no threshold ecn percentage

Syntax Description

bc

Specifies threshold for committed traffic. This keyword is not available for Frame Relay over MPLS.

be

Specifies threshold for excess traffic. This keyword is not available for Frame Relay over MPLS.

percentage

Threshold at which ECN bits will be set on packets, specified as a percentage of maximum queue size. Default is 100 percent.


Defaults

An ECN threshold is not configured.

Command Modes

Frame Relay congestion management configuration

Command History

Release
Modification

12.1(2)T

This command was introduced.

12.0(26)S

This command was modified for Frame Relay over MPLS.

12.2(27)SXA

This command was integrated into Cisco IOS Release 12.2(27)SXA.

12.2(28)SB

This command was integrated into Cisco IOS Release 12.2(28)SB.


Usage Guidelines

You must enable Frame Relay congestion management on the interface before congestion management parameters will be effective. To enable Frame Relay congestion management and to enter Frame Relay congestion management configuration mode, use the frame-relay congestion-management interface command.

Frame Relay Switching Guidelines

You must enable Frame Relay switching, using the frame-relay switching global command, before the threshold ecn command will be effective on switched PVCs.

You can configure separate queue thresholds for committed and excess traffic.

Configure the BECN threshold so that it is greater than or equal to zero and less than or equal to the BECN threshold. Configure the BECN threshold so that it is less than or equal to 100.

Examples

Frame Relay Switching Example

The following example shows how to configure a Be threshold of 0 and a Bc threshold of 20 percent on serial interface 1.

interface serial1
encapsulation frame-relay
frame-relay congestion-management
threshold ecn be 0
threshold ecn bc 20

Frame Relay over MPLS Example

The following example shows a configuration of interface serial2/1 for a threshold of 50 percent.

interface Serial2/1
bandwidth 50000
service-policy output output-policy
frame-relay congestion-management
threshold ecn 50

Related Commands

Command
Description

frame-relay congestion-management

Enables Frame Relay congestion management functions on all switched PVCs on an interface, and enters congestion management configuration mode.

frame-relay switching

Enables PVC switching on a Frame Relay DCE or NNI.