Configure Multilink PPP over Serial Interface Links
Introduction      Requirements      Multilink PPP Overview      Configure Multilink PPP      Verify your Configuration      Next Step      Troubleshoot the Procedure      Related Information	Download PDF   Configure Multilink PPP over Serial Interface Links

Introduction

This document describes how to configure Multilink PPP over Serial interface links to reduce latency and jitter for real-time traffic on a Cisco router.

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Requirements

To perform the steps described in this document, you need to have these items:

• Complete the initial configuration in Configure Your Router with Security Device Manager document.

• Complete the LAN Addressing Worksheet from the Site Survey.

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Multilink PPP Overview

A multilink bundle is a virtual PPP connection over a network link. The transmitting multilink bundle transmits the packet over a network link to a receiving multilink bundle, where the multilink bundle reassembles the fragments using the sequence number in the multilink header of the fragment. The individual member links in a multilink bundle are standard serial PPP connections.

Multilink PPP provides a method to split, recombine, and sequence datagram’s across multiple logical data links. Multilink PPP allows packets to fragment, and the fragments to be sent at the same time over multiple point-to-point links to the same remote address. This way, Multilink PPP improves throughput and reduces latency between systems. Before using Multilink PPP over serial interface links, a traffic policy (also known as a policy map) must be created. A policy map contains a traffic class, which is used to classify traffic, and one or more QoS feature.

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Configure Multilink PPP

Follow these steps to configure multilink PPP on serial interfaces:

1. Connect to the console of the router. Refer to Create a HyperTerminal Connection.

2. Enter into the interface configuration mode.

   Router#configure terminal
   Enter configuration commands, one per line.  End with CNTL/Z.
   Router(config)# 
   

3. Define an access list to match the traffic to be sent via the multilink PPP using access-list command followed by a number. This access list permits all ip traffic.

   Router(config)#access-list 101 permit ip any any
   

4. Create a class using the class-map command followed by a name. Map the newly created access list to this class using the match command.

   Router(config)#class-map class1
   Router(config-cmap)#match access-group 101
   Router(config-cmap)#exit
   

5. Create a traffic policy using the policy-map command followed by a name. Map the newly created class to this policy using the class command followed by class name.

   Router(config)#policy-map policy1
   Router(config-pmap)#class class1
   Router(config-pmap-c)#exit
   Router(config-pmap)#exit
   

6. Create a multilink bundle interface using interface multilink command followed by multilink bundle number.

   Router(config)#interface multilink 1
   

7. Assign a IP address to this interface using ip address command followed by an IP address and subnet mask.

   Router(config-if)#ip address 192.168.11.1 255.255.255.0
   

8. Attach the newly configured traffic policy using service-policy command followed by policy name in both input and output mode.

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

9. Specify the maximum delay time for packet fragments on the multilink PPP interface using ppp multilink fragment delay command followed by time in milliseconds.

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

10. Enable the interleaving of packets among the fragment of larger packets on multilink bundle using ppp multilink interleave command.

    Router(config-if)#ppp multilink interleave
    

11. To associate serial interface to multilink group, follow these steps:

    1. Enter into the interface using interface serial command followed by the slot and port number

    2. You can also specify a timeslot at the end of the command if you wish to use only the specific timeslot for multilink bundle

    Router(config-if)#interface serial 2/1
    

12. Set the interface encapsulation method as PPP using encapsulation ppp command. Also, enable multilink on the interface using ppp multilink command.

    Router(config-if)#encapsulation ppp
    Router(config-if)#ppp multilink
    

13. Assign this interface to the multilink bundle using ppp multilink group command followed by the multilink group number.

    Router(config-if)#ppp multilink group 1
    

14. Disable WFQ or DWFQ queuing methods on this serial interface using no fair-queue command.

    Router(config-if)#no fair-queue
    

    Repeat steps 11 to 14 to add other serial interfaces to this multilink bundle as required. Save this configuration by getting out of configuration mode using end command, and then enter the copy running-config startup-config command.

    Router(config-if)#end
    Router#copy running-config startup-config
    

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Verify your Configuration

Enter the show ppp multilink command, and check the output for multilink bundle uptime and its member list.

Router#show ppp multilink
   Multilink1, bundle name is Router2
   Bundle up for 00:01:39
   0 lost fragments, 0 reordered, 0 unassigned
   0 discarded, 0 lost received, 1/255 load
   0x3D received sequence, 0xB sent sequence
   Member links: 2 (max not set, min not set)
   Serial2/1, since 00:01:40, last rcvd seq 00003C
   Serial2/2, since 00:01:39, last rcvd seq 00003B

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Next Step

You have now configured multilink PPP over serial interface links.

Refer to Router Support Page to make further changes to your router.

Refer to Configuration Overview Page to configure other devices in your network.

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Troubleshoot the Procedure

This section provides information about common problems that you may encounter. If this information does not solve your problem, contact the SMB Technical Assistance Center (SMB TAC) for assistance.

Problem	Cause(s) and Suggested Solution(s)
You have configured the passwords but unable to login to the router.	Perform password recovery refer to Manually Reset the Password on a Cisco Router.

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Related Information

• Router Support Page
• Site Survey
• Create a HyperTerminal Connection