Using Multilink PPP over Serial Interface Links

First Published: May 2, 2005
Last Updated: March 22, 2011

This module contains conceptual information and configuration tasks for using Multilink PPP over serial interface links. Multilink PPP is a method used to reduce latency and jitter for real-time traffic.

Finding Feature Information in This Module

Your software release may not support all the features documented in this module. 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 Using Multilink PPP over Serial Interface Links" section.

Use Cisco Feature Navigator to find information about platform support and Cisco IOS and Catalyst OS 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

•Prerequisites for Using Multilink PPP over Serial Interface Links

•Restrictions for Using Multilink PPP over Serial Interface Links

•Information About Using Multilink PPP over Serial Interface Links

•How to Configure Multilink PPP over Serial Interface Links

•Configuration Examples for Using Multilink PPP over Serial Interface Links

•Where to Go Next

•Additional References

•Feature Information for Using Multilink PPP over Serial Interface Links

Prerequisites for Using Multilink PPP over Serial Interface Links

Knowledge

•Be familiar with the concepts in the "Reducing Latency and Jitter for Real-Time Traffic Using Multilink PPP" module.

Enable Queueing Mechanism

•Multilink uses first-in first out (FIFO) queuing for queueing and interleaving packets. Other queueing mechanisms such as low latency queueing (LLQ), weighted fair queueing (WFQ), and class-based weighted fair queueing (CBWFQ) can be used. If you want to use one of these alternative mechanisms, enable it before configuring multilink.

Restrictions for Using Multilink PPP over Serial Interface Links

Number of Links per Multilink Bundle

If a multilink bundle has one link or packet order is not important for interleaved packets, use Link Fragmentation and Interleaving (LFI) without multiclass. Use LFI with multiclass if a multilink bundle has multiple links.

VoIP Support

Only Voice over IP (VoIP) is supported.

Queueing Mechanisms Not Supported

Many of the legacy queueing mechanisms are not supported by multilink. These mechanisms include:

•Fair queueing on a virtual template interface

•Weighted random early detection (WRED) on a virtual template interface

•Custom queueing

•Priority queueing

Note Fair queueing, WRED, and priority queueing can be configured in a traffic policy using the Modular Quality of Service (QoS) Command-Line Interface (CLI) (MQC).

Information About Using Multilink PPP over Serial Interface Links

To use Multilink PPP over serial interface links, you should understand the following concept:

•MQC and Multilink PPP over Serial Interface Links

•Multilink Group Interfaces

MQC and Multilink PPP over Serial Interface Links

Before using Multilink PPP over serial interface links, a traffic policy (also known as a policy map) must be created. (See the "Prerequisites" section.) Policy maps are created using the Modular Quality of Service (QoS) Command-Line Interface (CLI) (MQC).

The MQC is a CLI structure that allows users to create traffic polices (policy maps) and attach these policy maps to interfaces. A policy map contains a traffic class and one or more QoS features. A traffic class is used to classify traffic. The QoS features in the traffic policy determine how to treat the classified traffic.

Multilink Group Interfaces

A multilink group interface is a collection of interfaces bundled together in the multilink PPP configuration. With a multilink group interface, you can bundle interfaces into logical multilink groups.

How to Configure Multilink PPP over Serial Interface Links

This section contains the following procedures:

•Configuring Multilink PPP over Serial Interface Links on a Multilink Group Interface (required)

•Associating the Serial Interface with the Multilink Group (required)

•Verifying the Multilink PPP over Serial Interface Link Configuration (optional)

Configuring Multilink PPP over Serial Interface Links on a Multilink Group Interface

Prerequisites

Before proceeding with this task, you must create a policy map. The policy map contains the configuration parameters used to apply the specific quality of service feature to the network traffic. To create a policy map, use the MQC. See the "MQC and Multilink PPP over Serial Interface Links" section.

SUMMARY STEPS

1. enable

2. configure terminal

3. interface multilink multilink-bundle-number

4. ip address ip-address mask [secondary]

5. service-policy output policy-map-name

6. service-policy input policy-map-name

7. ppp multilink fragment delay milliseconds [microseconds]

8. ppp multilink interleave

9. ppp multilink multiclass

10. 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 

interface multilink multilink-bundle-number

Example:

Router(config)# interface multilink 1

Creates a multilink bundle and enters interface configuration mode.

•Enter the multilink bundle number.

Step 4  

ip address ip-address mask [secondary]
Example: 
Router(config-if)# ip address 10.10.100.1 
255.255.255.0

Sets a primary IP address for an interface. This command can also set the optional secondary IP address for an interface.

•Enter the primary IP address (and, optionally, the secondary IP address).

Step 5  

service-policy output policy-map-name
Example:

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

Attaches the previously created QoS traffic policy (policy map). See the "Prerequisites" section. The policy map evaluates and applies QoS features for traffic leaving the interface.

•Enter the policy map name.

Step 6  

service-policy input policy-map-name
Example:

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

Attaches the previously created QoS traffic policy (policy map). See the "Prerequisites" section. The policy map evaluates and applies QoS features for traffic entering the interface.

•Enter the policy map name.

Step 7 

ppp multilink fragment delay milliseconds [microseconds]

Example:

Router(config-if)# ppp multilink fragment delay 20

Specifies a maximum size in units of time for packet fragments on a Multilink PPP (MLP) bundle.

•Enter the maximum amount of time, in milliseconds.

Step 8 

ppp multilink interleave

Example:

Router(config-if)# ppp multilink interleave

Enables interleaving of packets among the fragments of larger packets on a multilink bundle.

Step 9 

ppp multilink multiclass

Example:

Router(config-if)# ppp multilink multiclass

(Optional) Enables Multiclass Multilink PPP (MCMP) on an interface.

Note Use this command only if there are multiple links in the multilink bundle.

Step 10 

end

Example:

Router(config-if)# end

(Optional) Exits interface configuration mode.

Associating the Serial Interface with the Multilink Group

SUMMARY STEPS

1. enable

2. configure terminal

3. interface serial slot/port:timeslot

4. no fair-queue

5. encapsulation ppp

6. ppp multilink

7. ppp multilink group group-number

8. 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 

interface serial slot/port:timeslot

Example:

Router# interface serial 4/1:23


Specifies a serial interface created on a channelized E1 or channelized T1 controller (for ISDN PRI, channel-associated signaling, or robbed-bit signaling), and enters interface configuration mode.

•Enter the slot number and port number where the channelized E1 or T1 controller is located.

Step 4 

no fair-queue

Example:

Router(config-if)# no fair-queue

Disables WFQ (or DWFQ for VIP-enabled routers).

Step 5 

encapsulation ppp

Example:

Router(config-if)# encapsulation ppp

Sets the serial interface encapsulation method used by the interface.

Step 6 

ppp multilink

Example:

Router(config-if)# ppp multilink

Enables Multilink on an interface.

Step 7 

ppp multilink group group-number

Example:

Router(config-if)# ppp multilink group 1

Restricts a physical link to joining only a designated multilink group interface.

•Enter the multilink group number.

Step 8 

end

Example:

Router(config-if)# end

(Optional) Exits interface configuration mode.

Verifying the Multilink PPP over Serial Interface Link Configuration

SUMMARY STEPS

1. enable

2. show interfaces [type number] [first] [last] [accounting]

3. show ppp multilink [active | inactive | interface bundle-interface | [username name] [endpoint endpoint]]

4. show policy-map interface interface-name [vc [vpi/] vci] [dlci dlci] [input | output]

5. exit

DETAILED STEPS

 
Command or Action
Purpose

Step 1 

enable

Example:

Router> enable

Enables privileged EXEC mode.

•Enter your password if prompted.

Step 2  

show interfaces [type number] [first] [last] 
[accounting]
Example:

Router# show interfaces

(Optional) Displays statistics for all interfaces configured on the router or access server.

Step 3  

show ppp multilink [active | inactive | 
interface bundle-interface | [username name] 
[endpoint endpoint]]
Example:

Router# show ppp multilink

(Optional) Displays bundle information for mutlilink bundles.

Step 4  

show policy-map interface interface-name [vc 
[vpi/] vci] [dlci dlci] [input | output]
Example:

Router# show policy-map interface serial0/0

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

Step 5 

exit

Example:

Router# exit

(Optional) Exits privileged EXEC mode.

Configuration Examples for Using Multilink PPP over Serial Interface Links

This section contains the following examples:

•Configuring Multilink PPP over Serial Interface Links on a Multilink Group Interface: Example

•Associating the Serial Interface with the Multilink Group: Example

•Verifying the Multilink PPP over Serial Interface Link Configuration: Example

Configuring Multilink PPP over Serial Interface Links on a Multilink Group Interface: Example

The following is an example of configuring Multilink PPP over serial interface links on a multilink group interface:

Router> enable

Router# configure terminal

Router(config)# interface multilink 1 

Router(config-if)# ip address 10.10.100.1 255.255.255.0

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

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

Router(config-if)# ppp multilink fragment delay 20

Router(config-if)# ppp multilink interleave

Router(config-if)# ppp multilink multiclass

Router(config-if)# end


Associating the Serial Interface with the Multilink Group: Example

The following is an example of associating the serial interface serial4/1 with the multilink group:

Router> enable

Router# configure terminal

Router(config)# interface serial 4/1:23

Router(config-if)# no fair-queue

Router(config-if)# encapsulation ppp

Router(config-if)# ppp multilink

Router(config-if)# ppp multilink group 1

Router(config-if)# end


Verifying the Multilink PPP over Serial Interface Link Configuration: Example

You can verify the Multilink PPP over serial interface links configuration by using one or more of the following show commands:

•show interfaces

•show ppp multilink

•show policy-map interface

The following section provides sample output of the show ppp multilink command only. For sample output of the other commands, see the appropriate Cisco IOS Release 12.3 T command reference publication.

show ppp multilink Command Output Example

The following is an example of the show ppp multilink command output. In this example, one multilink bundle called 7206-2 is on the system. This bundle has two member links: one active link and one inactive link. 

Router# show ppp multilink


Multilink2, bundle name is 7206-2

  Endpoint discriminator is 7206-2

  Bundle up for 00:00:09, 1/255 load

  Receive buffer limit 12000 bytes, frag timeout 1500 ms

    0/0 fragments/bytes in reassembly list

    0 lost fragments, 0 reordered

    0/0 discarded fragments/bytes, 0 lost received

    0x0 received sequence, 0x3 sent sequence

  Member links:1 active, 1 inactive (max not set, min not set)

    Se3/2, since 00:00:10, 240 weight, 232 frag size

    Se3/3 (inactive)

Where to Go Next

To use Multilink PPP over ATM links, see the "Using Multilink PPP over ATM Links" module.

To use Multilink PPP over Frame Relay, see the "Using Multilink PPP over Frame Relay" module.

To use Multilink PPP over dialer interface links, see the "Using Multilink PPP over Dialer Interface Links" module.

Additional References

The following sections provide references related to Multilink PPP over serial interface links:

Related Documents

Related Topic
Document Title

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

Cisco IOS Quality of Service Solutions Command Reference

LLQ, WFQ, CBWFQ, PQ, CQ, FIFO and other queueing mechanisms

"Configuring Weighted Fair Queueing" module

MQC

"Applying QoS Features Using the MQC" module

Multilink PPP configurations

"Configuring Media-Independent PPP and Multilink PPP" module

Multilink PPP overview module

"Reducing Latency and Jitter for Real-Time Traffic Using Multilink PPP" module

Multilink PPP over ATM links (including ATM interfaces and ATM PVCs)

"Using Multilink PPP over ATM Links" module

Multilink PPP over Frame Relay

"Using Multilink PPP over Frame Relay" module

Multilink PPP over dialer interface links

"Using Multilink PPP over Dialer Interface Links" 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 releases, and feature sets, use Cisco MIB Locator found at the following URL:

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


RFCs

RFC
Title

RFC 1990

The PPP Multilink Protocol (MP)

RFC 2686

Multiclass Extension to Multilink PPP (MCML)


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 Using Multilink PPP over Serial Interface Links

Table 1 lists the release history for this feature.

Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco IOS and Catalyst OS 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 1 lists only the Cisco IOS software release that introduced support for a given feature in a given Cisco IOS software release train. Unless noted otherwise, subsequent releases of that Cisco IOS software release train also support that feature.

Table 1 Feature Information for Using Multilink PPP over Serial Interface Links

Feature Name
Software Releases
Feature Configuration Information

Distributed Link Fragmentation and Interleaving Over Leased Lines

12.2(8)T

The Distributed Link Fragmentation and Interleaving over Leased Lines feature extends distributed link fragmentation and interleaving functionality to leased lines.

This feature was extensively rewritten from the perspective of using Multilink PPP for link fragmentation and interleaving over serial interface links.

The following sections provide information about this feature:

•Information About Using Multilink PPP over Serial Interface Links

•How to Configure Multilink PPP over Serial Interface Links

Distributed Link Fragmentation and Interleaving for Frame Relay and ATM Interfaces on Cisco 7500 Series Routers

12.2(4)T

The Distributed Link Fragmentation and Interleaving (dLFI) for Frame Relay and ATM Interfaces on Cisco 7500 Series Routers feature extends link fragmentation and interleaving functionality to VIP-enabled Cisco 7500 series routers.

This feature was extensively rewritten from the perspective of using Multilink PPP for link fragmentation and interleaving over serial interface links.

The following sections provide information about this feature:

•Information About Using Multilink PPP over Serial Interface Links

•How to Configure Multilink PPP over Serial Interface Links


Cisco and the Cisco Logo are trademarks of Cisco Systems, Inc. and/or its affiliates in the U.S. and other countries. A listing of Cisco's trademarks can be found at www.cisco.com/go/trademarks. Third party trademarks mentioned are the property of their respective owners. The use of the word partner does not imply a partnership relationship between Cisco and any other company. (1005R)

Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental.

© 2011 Cisco Systems, Inc. All rights reserved.