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Cisco IOS Software Releases 12.2 T

Distributed Link Fragmentation and Interleaving over Leased Lines

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Table Of Contents

Distributed Link Fragmentation and Interleaving over Leased Lines

Feature Overview

Benefits

Restrictions

Related Features and Technologies

Related Documents

Supported Platforms

Supported Standards, MIBs, and RFCs

Prerequisites

Cisco 7500 Series Routers Prerequisites

Cisco 7600 Series Router Prerequisites

Configuration Tasks

Configuring LFI Using MLP over Frame Relay

Configuring Distributed Low Latency Queueing and Other QoS Features in a Traffic Policy

Configuring LFI Using MLP on a Virtual Template Interface

Associating the Virtual Template Interface with a Frame Relay PVC

Configuring LFI Using MLP over ATM

Configuring Distributed Low Latency Queueing and Other QoS Features in a Traffic Policy

Configuring LFI Using MLP in a Virtual Template Interface

Associating the Virtual Template Interface with an ATM PVC

Configuring LFI Using MLP over a Leased Line

Configuring Distributed Low Latency Queueing and Other QoS Features in a Traffic Policy

Configuring the Channel Group

Creating a Multilink Group

Assigning an Interface to a Multilink Group

Verifying LFI for Frame Relay, ATM, or Leased Lines

Monitoring and Maintaining LFI for Frame Relay, ATM, or Leased Lines

Configuration Examples

LFI over Frame Relay Configuration Example

LFI over ATM Configuration Example

LFI over Leased Line Configuration Example

Monitoring LFI Example

Command Reference

ppp multilink interleave

Glossary


Distributed Link Fragmentation and Interleaving over Leased Lines

Table 1 Feature History 

Cisco IOS Release
Modification

12.2(4)T3

The Distributed Link Fragmentation and Interleaving feature was introduced. This version of the feature supported Distributed Link Fragmentation and Interleaving for ATM and Frame Relay.

12.2(8)T

The Distributed Link Fragmentation and Interleaving over Leased Lines feature was introduced. This feature introduced Distributed Link Fragmentation and Interleaving on leased lines.

12.0(24)S

The Distributed Link Fragmentation and Interleaving over Leased Lines feature was introduced on Cisco IOS Release 12.0 S. This feature introduced Distributed Link Fragmentation and Interleaving on leased lines. Distributed Link Fragmentation and Interleaving is not available for ATM and Frame Relay using Cisco IOS Release 12.0 S.

12.2(14)SX

The Distributed Link Fragmentation and Interleaving feature was introduced on the Catalyst 6500 series switch and Cisco 7600 series router FlexWAN module.

This document describes the Distributed Link Fragmentation and Interleaving over Leased Lines feature. It includes information such as the benefits of the new feature, related documents, and supported platforms.

This document contains the following sections:

•Feature Overview

•Supported Platforms

•Supported Standards, MIBs, and RFCs

•Prerequisites

•Configuration Tasks

•Monitoring and Maintaining LFI for Frame Relay, ATM, or Leased Lines

•Configuration Examples

•Command Reference

•Glossary

Feature Overview

The Distributed Link Fragmentation and Interleaving over Leased Lines feature extends distributed link fragmentation and interleaving functionality to leased lines. Previously, Distributed Link Fragmentation and Interleaving was only available for Frame Relay and ATM on Cisco IOS Release 12.2 T. Distributed Link Fragmentation and Interleaving is not available for Frame Relay and ATM using Cisco IOS Release 12.0 S.

Note Distributed Link Fragmentation and Interleaving for Frame Relay, ATM, and Leased Lines is often referred to as dLFI in this document. This document covers the procedures for configuring dLFI on Frame Relay and ATM in addition to covering the procedure for configuring dLFI on a leased line.

The dLFI feature supports the transport of real-time traffic, such as voice, and non-real-time traffic, such as data, on lower-speed Frame Relay and ATM virtual circuits (VCs) and on leased lines without causing excessive delay to the real-time traffic.

This feature is implemented using multilink PPP (MLP) over Frame Relay, ATM, and leased lines on. The feature enables delay-sensitive real-time packets and non-real-time packets to share the same link by fragmenting the large data packets into a sequence of smaller data packets (fragments). The fragments are then interleaved with the real-time packets. On the receiving side of the link, the fragments are reassembled and the packet reconstructed.

The dLFI feature is often useful in networks that send real-time traffic using Distributed Low Latency Queueing, such as voice, but have bandwidth problems that delay this real-time traffic due to the transport of large, less time-sensitive data packets. The dLFI feature can be used in these networks to disassemble the large data packets into multiple segments. The real-time traffic packets then can be sent between these segments of the data packets. In this scenario, the real-time traffic does not experience a lengthy delay waiting for the low-priority data packets to traverse the network. The data packets are reassembled at the receiving side of the link, so the data is delivered intact.

The ability to configure Quality of Service (QoS) using the Modular Quality of Service (QoS) Command-Line Interface (CLI) (MQC) while also using distributed MLP (dMLP) is also introduced as part of the dLFI feature. The ability to configure QoS using the MQC while using dMLP was not supported prior to the introduction of the dLFI feature.

The following figure illustrates how dLFI fragments a larger data packet to allow time-sensitive traffic, in this case voice traffic, to be delivered in a more timely manner.

Figure 1 Distributed Link Fragmentation and Interleaving Example

Benefits

End-to-End Voice over IP Quality

This new feature enhances Voice over IP (VoIP) QoS by preventing delay, delay variation (jitter), and packet loss for voice traffic on low speed ATM-to-ATM and ATM-to-Frame Relay networks and on leased lines.

Interoperability with Other QoS Features

The dLFI feature works concurrently with and on the same switching path as other QoS features, ensuring high quality and scalable VoIP deployment.

The dLFI feature works in conjunction with most of the following QoS features:

•Distributed Low Latency Queueing (dLLQ, the priority command)

•Distributed Traffic Shaping (dTS, the shape command)

•Distributed Compressed Real-Time Transport Protocol (dCRTP, the ip [rtp | tcp] connections and other compression commands)

•Distributed Class-Based Weighted Fair Queueing (dCBWFQ, the bandwidth, fair-queue, and queue-limit commands)

•Distributed Weighted Random Early Detection (dWRED, the random-detect command)

•Class-Based Marking (the set command)

•Traffic Policing (the police command)

Increased Call Support for Voice on VIP-Enabled Cisco 7500 Series Routers

The dLFI feature enhances the scalability on interfaces and Permanent Virtual Circuits (PVCs), thereby allowing support for additional calls on VIP-enabled Cisco 7500 series routers.

Restrictions

The following restrictions apply to the Distributed Link Fragmentation and Interleaving feature:

Queuing Mechanisms Supported

•Many of the older queueing mechanisms are not supported by dLFI. These mechanisms include:

–Fair-queueing on a virtual template interface

–Random-detect on a virtual template interface

–Custom queueing

–Priority queueing

Note Fair queueing, random detection (dWRED), and priority queueing can be configured in a traffic policy using the Modular QoS CLI.

CRTP Configurations

•Compressed Real-Time Transport Protocol (CRTP) configurations should not be configured on the multilink interface when the following feature combination is configured:

–Link Fragmentation and Interleaving (LFI) is enabled on the multilink interface

–The multilink bundle has more than one member link

–QoS policy with a priority feature is enabled on the multilink interface

Note In a dMLP/dLFI configuration, priority packets do not carry MLP header and sequence number. Thus, MLP distributes the priority packets across all member links. As a result, packets that are compressed by CRTP may arrive out-of-order at the receiving router. This prohibits CRTP from decompressing the packet header and forces CRTP to drop the packets.

MLP Bundle Support

•Only one link per MLP bundle is supported when using dLFI over Frame Relay or dLFI over ATM. If more than one link is used in an MLP bundle when using dLFI over Frame Relay or dLFI over ATM, dLFI is automatically disabled. When using dLFI over leased lines, more than one link can be configured with dLFI in the MLP bundle.

QoS traffic policies will function properly in MLP bundles with more than one link, however.

VoIP Support

•Only Voice over IP (VoIP) is supported; Voice over Frame Relay and Voice over ATM are not supported by the dLFI feature.

QoS Policies Attached in an ATM Interface

•QoS policies can be attached to either subinterfaces or permanent virtual circuits (PVCs) with the ATM interface. As a general rule, the QoS policies must be attached the same way across the entire ATM interface. That is, all the QoS policies must be attached to either subinterfaces or PVCs, not a combination of subinterfaces and PVCs.

Note However, dLFI can be enabled on a PVC only. Therefore, if dLFI is enabled, dLFI requires that the QoS policy be attached at the PVC level for all the PVCs within the ATM interface. A QoS policy attached at the subinterface level is rejected.

QoS Policies Attached in a Frame Relay Network

•QoS policies can be attached to either a Frame Relay map-class or a subinterface within the Frame Relay network. As a general rule, the QoS policies must be attached the same way across the entire Frame Relay network. That is, all the QoS policies must be attached to either the Frame Relay map-class or the subinterface, not a combination of Frame Relay map-classes and subinterfaces.

Note If FRF.12 is enabled, dLFI requires that the QoS policy be attached to the Frame Relay map-class. A QoS policy attached to the subinterface is rejected.

Related Features and Technologies

•Frame Relay/ATM interworking (FRF.8)

•Distributed Frame Relay fragmentation (FRF.12)

•Distributed Multilink Point-to-Point Protocol (dMLP)

•The dLFI feature works in conjunction with most Quality of Service (QoS) features, including the QoS features listed below:

–Distributed Low Latency Queueing (dLLQ, the priority command)

–Distributed Traffic Shaping (dTS, the shape command)

–Distributed Compressed Real-Time Transport Protocol (dCRTP, the ip [rtp | tcp] connections and other compression commands)

–Distributed Class-Based Weighted Fair Queueing (dCBWFQ, the bandwidth, fair-queue, and queue-limit commands)

–Class-Based Marking (the set command)

–Traffic Policing (the police command)

Related Documents

•Distributed Low Latency Queueing, Cisco IOS Release 12.1(5)T feature module

•Cisco IOS Quality of Service Solutions Configuration Guide, Release 12.2

–"Modular Quality of Service Command-Line Interface" section of the Cisco IOS Quality of Service Solutions Configuration Guide, Release 12.2

•Cisco IOS Quality of Service Solutions Command Reference, Release 12.2

•Cisco IOS Wide-Area Networking Configuration Guide, Release 12.2

•Cisco IOS Wide-Area Networking Command Reference, Release 12.2

•Distributed Multilink Point-to-Point Protocol for Cisco 7500 Series Routers, Cisco IOS Release 12.0(3)T feature module

•Distributed Traffic Shaping, Cisco IOS Release 12.1(5)T feature module

•Distributed Compressed Real-Time Transport Protocol, Cisco IOS Release 12.1(5)T feature module

•Distributed Class-Based Weighted Fair Queueing, Cisco IOS Release 12.1(5)T feature module

Supported Platforms

•Cisco 7600 series routers and Catalyst 6500 series switches with a FlexWAN

•Cisco 7500 series routers with a VIP2-50 or higher

Note A VIP2-50 with a minimum of 64 MB DRAM and 4 MB SRAM or a VIP4-80 with a minimum of 128 MB SDRAM as program memory and 64 MB SDRAM as packet memory are required to run dLFI on the Cisco 7500 series routers. The VIP4-80 will provide better performance in most networking environments.

The "Prerequisites" section of this document details other requirements, including port adapter requirements.

Determining Platform Support Through Cisco Feature Navigator

Cisco IOS software is packaged in feature sets that are supported on specific platforms. To get updated information regarding platform support for this feature, access Cisco Feature Navigator. Cisco Feature Navigator dynamically updates the list of supported platforms as new platform support is added for the feature.

Cisco Feature Navigator is a web-based tool that enables you to determine which Cisco IOS software images support a specific set of features and which features are supported in a specific Cisco IOS image. You can search by feature or release. Under the release section, you can compare releases side by side to display both the features unique to each software release and the features in common.

To access Cisco Feature Navigator, you must have an account on Cisco.com. If you have forgotten or lost your account information, send a blank e-mail to cco-locksmith@cisco.com. An automatic check will verify that your e-mail address is registered with Cisco.com. If the check is successful, account details with a new random password will be e-mailed to you. Qualified users can establish an account on Cisco.com by following the directions found at this URL:

http://www.cisco.com/register

Cisco Feature Navigator is updated regularly when major Cisco IOS software releases and technology releases occur. For the most current information, go to the Cisco Feature Navigator home page at the following URL:

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

Supported Standards, MIBs, and RFCs

Standards

No new or modified standards are supported by this feature.

MIBs

No new or modified MIBs are supported by this feature.

To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, go to the Cisco MIB website on Cisco.com at the following URL:

http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml

RFCs

RFC 1990, The PPP Multilink Protocol (MP)

Prerequisites

The following prerequisites apply for support of dLFI on the Cisco 7500 series routers and on the Cisco 7600 series routers and Catalyst 6500 series switches with a FlexWAN:

•Cisco 7500 Series Routers Prerequisites

•Cisco 7600 Series Router Prerequisites

Cisco 7500 Series Routers Prerequisites

•The minimum required VIP for dLFI is a VIP2-50. A VIP2-50 with a minimum of 64 MB DRAM and 4 MB SRAM or a VIP4-80 with a minimum of 128 MB SDRAM as program memory and 64 MB SDRAM as packet memory is required to run dLFI. The VIP4-80 will provide better performance in most networking environments.

The amount of required DRAM and SRAM is proportional to the number of PVCs and interfaces; therefore, additional DRAM and SRAM might be necessary if additional PVCs or interfaces are added and VIP CPU is available. If VIP CPU has reached its maximum threshold, additional DRAM and SRAM will not be useful for adding additional PVCs or interfaces.

•RSP2 with a minimum of 64 MB of DRAM

•Distributed Low Latency Queueing (dLLQ). The interleaving of packets occurs only when a QoS traffic policy that contains a dLLQ configuration is attached to a PVC or an interface. If dLLQ is not configured on the PVC or interface, packets will be fragmented but not interleaved.

The priority policy map class command is used to configure dLLQ in a QoS traffic policy, and the service-policy interface command is used to attach the QoS traffic policy to an interface or a PVC.

•Distributed Cisco Express Forwarding (dCEF) must be globally enabled. You can enable dCEF using the ip cef distributed command in global configuration mode.

•A virtual template or a multilink interface must be shutdown and then re-enabled (using the shutdown command followed by the no shutdown command) to change any PPP configuration. The exception to this restriction is the QoS traffic policy, which does not require the shutdown/no shutdown sequence in order to be enabled.

•All currently available serial port adapters for the Cisco 7500 series routers support dLFI using MLP over Frame Relay. These port adapters include:

–PA-4T+

–PA-8T

–PA-MC-T3

–PA-CE3

–PA-MC-2E1/120

–PA-MC-2T1

–PA-MC-2T3+

–PA-MC-4T1

–PA-MC-8DSX1

–PA-MC-8E1/120

–PA-MC-8T1

–PA-MC-E3

•All currently available channelized serial port adapters for Cisco 7500 series routers support dLFI over leased lines. These port adapters include:

–PA-MC-2E1/120

–PA-MC-2T1

–PA-MC-2T3+

–PA-MC-4T1

–PA-MC-8DSX1

–PA-MC-8E1/120

–PA-MC-8T1

–PA-MC-E3

–PA-MC-STM1

•MLP over ATM must use a PA-A3 ATM port adapter. Therefore, only PA-A3 ATM port adapters support dLFI using MLP over ATM.

–PA-A3-E3

–PA-A3-OC3

–PA-A3-T3

Note The PA-A3 IMA port adapter is not supported by dLFI.

Cisco 7600 Series Router Prerequisites

The following prerequisites apply to dLFI support on the Cisco 7600 series routers and Catalyst 6500 series switches with a FlexWAN:

•Distributed Low Latency Queueing (dLLQ). The interleaving of packets occurs only when a QoS traffic policy that contains a dLLQ configuration is attached to a PVC or an interface. If dLLQ is not configured on the PVC or interface, packets will be fragmented but not interleaved.

The priority policy map class command is used to configure dLLQ in a QoS traffic policy, and the service-policy interface command is used to attach the QoS traffic policy to an interface or a PVC.

•A virtual template or a multilink interface must be shutdown and then re-enabled (using the shutdown command followed by the no shutdown command) to change any PPP configuration. The exception to this restriction is the QoS traffic policy, which does not require the shutdown/no shutdown sequence in order to be enabled.

•All currently available serial port adapters for the FlexWAN support LFI using MLP over Frame Relay:

–PA-4T+

–PA-8T

–PA-MC-T3

–PA-MC-2T3+

–PA-MC-4T1

–PA-MC-8E1/120

–PA-MC-8T1

–PA-MC-E3

•All currently available channelized serial port adapters for the FlexWAN support LFI over leased lines:

–PA-MC-2T3+

–PA-MC-4T1

–PA-MC-8E1/120

–PA-MC-8T1

–PA-MC-E3

–PA-MC-STM1

•MLP over ATM must use a PA-A3 ATM port adapter. The following PA-A3 ATM port adapters support LFI using MLP over ATM:

–PA-A3-E3

–PA-A3-OC3

–PA-A3-T3

Note The PA-A3 IMA port adapter is not supported by dLFI.

Configuration Tasks

See the following sections for configuration tasks for the dLFI feature. Each task in the list is identified as optional or required.

•Configuring LFI Using MLP over Frame Relay (required for configuring dLFI on Frame Relay. Not available on Cisco IOS Release 12.0 S)

•Configuring LFI Using MLP over ATM (required for configuring dLFI on ATM. Not available on Cisco IOS Release 12.0 S)

•Configuring LFI Using MLP over a Leased Line (required for configuring dLFI on a leased lines)

•Verifying LFI for Frame Relay, ATM, or Leased Lines (optional)

Configuring LFI Using MLP over Frame Relay

To configure LFI using MLP over Frame Relay, perform the tasks in the following sections:

•Configuring Distributed Low Latency Queueing and Other QoS Features in a Traffic Policy

•Configuring LFI Using MLP on a Virtual Template Interface

•Associating the Virtual Template Interface with a Frame Relay PVC

Configuring Distributed Low Latency Queueing and Other QoS Features in a Traffic Policy

The dLLQ feature must be enabled in order for the dLFI feature to interleave packet fragments. The dLLQ feature is configured in a QoS traffic policy, which is attached to the multilink group. Other QoS features can also be configured in the traffic policy.

A traffic policy using dLLQ and other QoS features can be configured by entering the following commands:

 
Command
Purpose

Step 1  

Router(config)# class-map [match-any | match-all] 
class-map-name

Specifies the user-defined name of the traffic class and enters class map configuration mode. A traffic class is used to classify traffic.

Step 2  

Router(config-cmap)# match match-criterion

Specifies the criteria to classify traffic against. If traffic matches the specified match criteria, traffic is said to belong to the traffic class.

Multiple match criterion can be specified in a single traffic class.

Step 3  

Router(config-cmap)# exit

Exits class map configuration mode.

Step 4  

Router(config)# policy-map policy-name

Specifies the name of the QoS traffic policy to configure and enters policy map configuration mode.

Step 5  

Router(config-pmap)# class class-map-name

Specifies the name of a predefined class included in the service policy. This traffic class classifies traffic; the QoS features configured in the traffic policy determine how to forward traffic that matches the traffic class configuration.

In these instructions, the class-map-name option should match the class-map-name entered in Step 1 of this procedure.

Step 6  

Router(config-pmap-c)# priority [percent] [kpbs | 
percent] [bytes]

Reserves a priority queue with a specified amount or percent of available bandwidth for high-priority traffic.

The priority command is used to enable dLLQ.

Step 7  

Router(config-pmap-c)#

Enables a QoS feature in the traffic policy.

Configuring LFI Using MLP on a Virtual Template Interface

To configure LFI using MLP on a virtual template interface, use the following interface configuration commands:

 
Command
Purpose

Step 1 

Router(config)# interface virtual-template number

Creates a virtual template and enters interface configuration mode.

Step 2 

Router(config-if)# bandwidth kilobits

Sets the bandwidth value for an interface. The bandwidth value for the interface should match the traffic speed of the PVC; for instance, if the VBR peak cell rate is 128 kpbs, the kilobits option in the bandwidth command should be entered as 128. Similarly, if the PVC is being shaped to 64 kpbs, the kilobits option should be entered as 64.

Step 3 

Router(config-if)# ip address ip-address mask

Sets a primary IP address for an interface.

Step 4 

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

(Required for traffic leaving the virtual template interface) Attaches a previously configured QoS traffic policy, which contains QoS classification and configuration parameters, that evaluates and applies QoS features for traffic leaving the interface with the virtual template.

The priority command must be configured in this traffic policy for dLFI to operate properly. In this example, the policy-name option should match the policy-name option given in Step 4 of the Configuring Distributed Low Latency Queueing and Other QoS Features in a Traffic Policy procedure.

Note For dLFI, the QoS traffic policy that is attached using the service-policy command is attached to the virtual template. The QoS traffic policy does not have to be attached to the Frame Relay map class.

Step 5 

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

(Required for traffic entering the virtual template interface) Attaches a previously configured QoS traffic policy, which contains QoS classification and configuration parameters, that evaluates and applies QoS features, including dLLQ, for traffic entering the interface with the virtual template.

The priority command must be configured in this traffic policy for dLFI to operate properly. In this example, the policy-name option should match the policy-name option given in Step 4 of the Configuring Distributed Low Latency Queueing and Other QoS Features in a Traffic Policy procedure.

Note For dLFI, the QoS traffic policy that is attached using the service-policy command is attached on the virtual template. The QoS traffic policy does not have to be attached to the Frame Relay map class.

Step 6 

Router(config-if)# ppp multilink

Enables MLP on the interface.

Step 7 

Router(config-if)# ppp multilink fragment-delay milliseconds

Configures the maximum delay allowed for transmission of a packet fragment on an MLP bundle.

Step 8 

Router(config-if)# ppp multilink interleave

Enables interleaving of packets among the fragments of larger packets on an MLP bundle.

Fragment size at the MLP bundle can be configured using the following formula:

fragment size = bandwidth x fragment-delay / 8

Associating the Virtual Template Interface with a Frame Relay PVC

To associate the virtual template interface with a Frame Relay PVC, use the following commands beginning in global configuration mode:

 
Command
Purpose

Step 1 

Router(config)# interface type number

Configures an interface type and enters interface configuration mode.

Step 2 

Router(config-if)# frame-relay interface-dlci dlci [ppp virtual-template-name]

Associates a virtual template interface with a Frame Relay DLCI.1

1 DLCI = data-link connection identifier

Configuring LFI Using MLP over ATM

LFI using MLP can be configured over ATM using a virtual template interface. To configure LFI using MLP over ATM using a virtual template interface, perform the tasks in the following sections:

•Configuring Distributed Low Latency Queueing and Other QoS Features in a Traffic Policy

•Configuring LFI Using MLP in a Virtual Template Interface

•Associating the Virtual Template Interface with an ATM PVC

Configuring Distributed Low Latency Queueing and Other QoS Features in a Traffic Policy

The dLLQ feature must be enabled in order for the dLFI feature to interleave packet fragments. The dLLQ feature is configured in a QoS traffic policy, which is attached to the multilink group. Other QoS features can also be configured in the traffic policy.

A traffic policy using dLLQ and other QoS features can be configured by entering the following commands:

 
Command
Purpose

Step 1  

Router(config)# class-map [match-any | match-all] 
class-map-name

Specifies the user-defined name of the traffic class and enters class map configuration mode. A traffic class is used to classify traffic.

Step 2  

Router(config-cmap)# match match-criterion

Specifies the criteria to classify traffic against. If traffic matches the specified match criteria, traffic is said to belong to the traffic class.

Multiple match criterion can be specified in a single traffic class.

Step 3  

Router(config-cmap)# exit

Exits class map configuration mode.

Step 4  

Router(config)# policy-map policy-name

Specifies the name of the QoS traffic policy to configure and enters policy map configuration mode.

Step 5  

Router(config-pmap)# class class-map-name

Specifies the name of a predefined class included in the service policy. This traffic class classifies traffic; the QoS features configured in the traffic policy determine how to forward traffic that matches the traffic class configuration.

In these instructions, the class-map-name option should match the class-map-name entered in Step 1 of this procedure.

Step 6  

Router(config-pmap-c)# priority [percent] [kpbs | 
percent] [bytes]

Reserves a priority queue with a specified amount or percentage of available bandwidth for high-priority traffic.

The priority command is used to enable dLLQ.

Step 7  

Router(config-pmap-c)#

Enables a QoS feature in the traffic policy.

Configuring LFI Using MLP in a Virtual Template Interface

To configure dLFI using MLP on a virtual template interface, use the following interface configuration commands:

 
Command
Purpose

Step 1 

Router(config)# interface virtual-template number

Creates a virtual template and enters interface configuration mode.

Step 2 

Router(config-if)# bandwidth kilobits

Sets the bandwidth value for an interface.

Step 3 

Router(config-if)# ip address ip-address mask

Sets a primary IP address for an interface.

Step 4 

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

(Required for traffic leaving the virtual template interface) Attaches a previously configured QoS traffic policy, which contains QoS classification and configuration parameters, that evaluates and applies QoS features, including dLLQ, for traffic leaving the interface with the virtual template.

The priority command must be configured in this traffic policy for dLFI to operate properly. In this example, the policy-name option should match the policy-name option given in Step 4 of the Configuring Distributed Low Latency Queueing and Other QoS Features in a Traffic Policy procedure.

Note For dLFI, the QoS traffic policy that is attached using the service-policy command is attached to the virtual template. The QoS traffic policy does not have to be attached to the ATM PVC.

Step 5 

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

(Required for traffic entering the virtual template interface) Attaches a previously configured QoS traffic policy, which contains QoS classification and configuration parameters, that evaluates and applies QoS features, including dLLQ, for traffic entering the interface with the virtual template.

The priority command must be configured in this traffic policy for dLFI to operate properly. In this example, the policy-name option should match the policy-name option given in Step 4 of the Configuring Distributed Low Latency Queueing and Other QoS Features in a Traffic Policy procedure.

Note For dLFI, the QoS traffic policy that is attached using the service-policy command is attached to the virtual template. The QoS traffic policy does not have to be attached to the ATM PVC.

Step 6 

Router(config-if)# ppp multilink

Enables MLP on the interface.

Step 7 

Router(config-if)# ppp multilink fragment-delay milliseconds

Configures the maximum delay allowed for transmission of a packet fragment on an MLP bundle.

Step 8 

Router(config-if)# ppp multilink interleave

Enables interleaving of packets among the fragments of larger packets on an MLP bundle.

Fragment size at the MLP bundle can be configured using the following formula:

fragment size = bandwidth x fragment-delay / 8

The ideal fragment size for MLP over ATM should allow the fragments to fit into an exact multiple of ATM cells. The fragment size for MLP over ATM can be calculated using the following formula:

fragment size = 48 x number of cells - 10

Associating the Virtual Template Interface with an ATM PVC

To associate the virtual template interface with an ATM PVC, use the following commands beginning in global configuration mode:

 
Command
Purpose

Step 1 

Router(config)# interface atm slot/0

or

Router(config)# interface atm slot/port

Specifies the ATM interface type and enters interface configuration mode.1

Step 2 

Router(config-if)# pvc [name] vpi/vci

Creates an ATM PVC.

Step 3 

Router(config-if-atm-vc)# abr output-pcr output-mcr

Selects ABR2 QoS and configures the output peak cell rate and output minimum guaranteed cell rate for an ATM PVC.

Step 4 

Router(config-if-atm-vc)# protocol ppp virtual-template number

Specifies that PPP is established over the ATM PVC using the configuration from the specified virtual template.

1 To determine the correct form of the interface atm command, consult your ATM network module, port adapter, or router documentation.

2 ABR = available bit rate

Configuring LFI Using MLP over a Leased Line

LFI over a leased line can be configured using MLP. To configure LFI over a leased line, perform the tasks in the following sections:

•Configuring Distributed Low Latency Queueing and Other QoS Features in a Traffic Policy

•Assigning an Interface to a Multilink Group

•Configuring the Channel Group

•Creating a Multilink Group

•Assigning an Interface to a Multilink Group

Configuring Distributed Low Latency Queueing and Other QoS Features in a Traffic Policy

The dLLQ feature must be enabled in order for the dLFI feature to interleave packet fragments. The dLLQ feature is configured in a QoS traffic policy which is attached to the multilink group. Other QoS features can also be configured in the traffic policy.

A traffic policy using dLLQ and other QoS features can be configured by entering the following commands:

 
Command
Purpose

Step 1  

Router(config)# class-map [match-any | match-all] 
class-map-name

Specifies the user-defined name of the traffic class and enters class map configuration mode. A traffic class is used to classify traffic.

Step 2  

Router(config-cmap)# match match-criterion

Specifies the criteria to classify traffic against. If traffic matches the specified match criteria, traffic is said to belong to the traffic class.

Multiple match criterion can be specified in a single traffic class.

Step 3  

Router(config-cmap)# exit

Exits class map configuration mode.

Step 4  

Router(config)# policy-map policy-name

Specifies the name of the QoS traffic policy to configure and enters policy map configuration mode.

Step 5  

Router(config-pmap)# class class-map-name

Specifies the name of a predefined class included in the service policy. This traffic class classifies traffic; the QoS features configured in the traffic policy determine how to forward traffic that matches the traffic class configuration.

In these instructions, the class-map-name option should match the class-map-name entered in Step 1 of this procedure.

Step 6  

Router(config-pmap-c)# priority [percent] [kpbs | 
percent] [bytes]

Reserves a priority queue with a specified amount or percentage of available bandwidth for high-priority traffic.

The priority command is used to enable dLLQ.

Step 7  

Router(config-pmap-c)#

Enables a QoS feature in the traffic policy.

Note The bandwidth command can be used in a QoS traffic policy to specify an amount of bandwidth to be reserved for the traffic policy. If the bandwidth command is used in a traffic policy that will be attached to a multilink interface, the following guidelines should be followed:
1. Use bandwidth percent in favor of bandwidth kpbs if possible. If the bandwidth kpbs option is specified as member links join and leave the bundle, the bandwidth setting will not adjust to the new aggregate bandwidth and the QoS traffic policy will either consume more bandwidth than desired or not have enough available bandwidth. Because the bandwidth percent option adjusts accordingly when new members links are added or removed, the amount of available bandwidth is properly adjusted when new member links are added or removed.
2. If bandwidth kpbs must be used, specify a bandwidth statement for the multilink group to reflect the expected available bandwidth for the multilink group. This bandwidth should be identical to the amount of bandwidth specified in the channel configuration when the channel-group command is entered (See Step 2 in the "Configuring the Channel Group" section of this document). For instance, if two channels are defined using the DS0 rate (64 kpbs), the kilobits variable should be entered as 128.

Configuring the Channel Group

A channel group is used to configure the controllers. To configure the controller, enter the following commands:

 
Command
Purpose

Step 1  

Router(config)# controller [t1 | e1] slot/port

Configures a T1 or E1 controller.

Step 2  

Router(config-controller)# channel-group 
channel-number timeslots range [speed {48 | 56 | 64}]

Defines the time slots that belong to each T1 or E1 circuit.

Creating a Multilink Group

To create a multilink group, use the following commands beginning in interface configuration mode:

 
Command
Purpose

Step 1 

Router(config)# interface multilink group-number

Creates and names a multilink bundle. The name of the multilink bundle is the group-number.

Step 2 

Router(config-if)# ip address ip-address mask

Assigns an IP address for the multilink group.

Step 3 

Router(config-if)# bandwidth kilobits

(Optional, unless a QoS traffic policy using the bandwidth kpbs command will be attached to the multilink group) Sets the bandwidth value for an interface.

The bandwidth should match the parameters defined in channel configuration. For instance, if two channels are defined using the DS0 rate (64 kpbs), the kilobits variable should be entered as 128.

Step 4 

Router(config-if)# ppp multilink

Enables MLP for the multilink group.

Step 5 

Router(config-if)# ppp multilink fragment-delay milliseconds

Configures the maximum delay allowed for transmission of a packet fragment on an MLP bundle.

Step 6 

Router(config-if)# ppp multilink interleave

Enables interleaving of packets among the fragments of larger packets on an MLP bundle.

Step 7 

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

(Required for traffic leaving the multilink group) Attaches a previously configured QoS traffic policy, which contains QoS classification and configuration parameters, that evaluates and applies QoS features, including dLLQ, for traffic leaving the interface bundle.

The priority command must be configured in this traffic policy for dLFI to operate properly. In this example, the policy-name option should match the policy-name option given in Step 4 of the Configuring Distributed Low Latency Queueing and Other QoS Features in a Traffic Policy procedure.

Note For dLFI, the QoS traffic policy that is attached using the service-policy command is entered in the multilink group. The QoS traffic policy does not have to be attached to the serial interface that is part of the group.

Step 8 

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

(Required for traffic entering the multilink group) Attaches a previously configured QoS traffic policy, which contains QoS classification and configuration parameters, that evaluates and applies QoS features, including dLLQ, for traffic entering the interface bundle.

The priority command must be configured in this traffic policy for dLFI to operate properly. In this example, the policy-name option should match the policy-name option given in Step 4 of the Configuring Distributed Low Latency Queueing and Other QoS Features in a Traffic Policy procedure.

Note For dLFI, the QoS traffic policy that is attached using the service-policy command is entered in the multilink group. The QoS traffic policy does not have to be attached to the serial interface that is part of the group.

Assigning an Interface to a Multilink Group

To configure an interface and attach the interface to a multilink group, use the following commands beginning in interface configuration mode:

 
Command
Purpose

Step 1 

Router(config)# interface serial interface-number

Specifies the serial interface to configure. Only serial interfaces can be bundled using multilink groups.

Step 2 

Router(config-if)# no ip address

Removes any specified IP address.

Step 3 

Router(config-if)# keepalive [seconds]

Sets the keepalive interval for the interface. The keepalive interval, which is the frequency at which the Cisco IOS software sends messages to itself or to the other end, is used to ensure a network interface is up. The seconds variable determines how often these messages are sent; for instance, if keepalive 5 is entered, a keepalive message is sent every 5 seconds.

Step 4 

Router(config-if)# ppp chap hostname hostname

Specifies the hostname for the interface when Challenge Handshake Authentication Protocol (CHAP) is used for authentication. The CHAP hostname must be configured in order to avoid potential errors when more than one multilink group exists between the same two routers.

A different hostname should be specified for each multilink group on a router.

Step 5 

Router(config-if)# ppp multilink

Enables multilink PPP for the interface.

Step 6 

Router(config-if)# multilink-group group-number

Assigns the interface to a multilink group. To assign the interface to a previously configured multilink group, the group-number variable in this step must match the group-number variable specified in the multilink group (in the "Creating a Multilink Group" section of this document, the group-number for the multilink group is specified in Step 1).

Verifying LFI for Frame Relay, ATM, or Leased Lines

To display information about LFI for Frame Relay, ATM, or leased lines using MLP, use the following privileged EXEC commands:

Command
Purpose

Router# show frame-relay pvc dlci

Displays statistics about PVCs for Frame Relay interfaces.

Router# show interfaces

Displays interleaving statistics. Interleaving data is displayed only if interleaving occurs.

Router# show ppp multilink

Displays bundle information for the MLP bundles and their PPP links in the router.

Router# show policy-map interface

Displays configurations and statistics of all input and output traffic policies attached to an interface.


Monitoring and Maintaining LFI for Frame Relay, ATM, or Leased Lines

To monitor LFI for Frame Relay, ATM, or leased lines using MLP, use the following privileged EXEC commands:

Command
Purpose

Router# show ppp multilink

Displays bundle information for the MLP bundles and their PPP links in the router. Displays dLFI statistics, including the number of fragmented, unfragmented, and reassembled packets, reassembly and fragmentation drops, and fragments that arrived out of sequence.

Router# debug ppp multilink fragments

Displays information about individual multilink fragments and important multilink events.

Router# debug voice RTP

Displays information about the interleaving of voice and data packets.


Note The debug ppp multilink fragments and debug voice RTP commands have memory overhead and should not be used when memory is scarce or when traffic is very high.

Configuration Examples

This section provides the following configuration examples:

•LFI over Frame Relay Configuration Example

•LFI over ATM Configuration Example

•LFI over Leased Line Configuration Example

•Monitoring LFI Example

LFI over Frame Relay Configuration Example

The following example shows the configuration of LFI using MLP over Frame Relay using a virtual template interface: 

class-map voip

  match ip precedence 5


class-map business

  match ip precedence 3



policy-map llq-policy

  class voip

    priority 32

  class business

    bandwidth 32



policy-map shape-llq-policy

  class class-default

    shape average 80000 320 320

    service-policy llq-policy



policy-map input-policy

  class voip

    police 32000 1500 1500 conform-action transmit exceed-action drop



controller T1 5/1/0

  framing esf

  linecode b8zs

  channel-group 0 timeslots 1-2



interface Serial5/1/0:0

  no ip address

  encapsulation frame-relay



interface Serial5/1/0:0.1 point-to-point

  frame-relay interface-dlci 20 ppp Virtual-Template2


interface Virtual-Template2