Router Installation and Configuration Manual/Configuring Multilink PPP for Load Balancing and Aggregation

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Introduction

This chapter describes how to configure the ImageStream router to use the Inetics Multilink PPP commands to load balance traffic across multiple circuits by aggregating multiple WAN devices. The Multilink commands are used to add aggregated devices on an interface-by-interface basis and to create the Multilink interfaces in the main WAN interface configuration file.
This chapter includes the following topics:
  • Configuring Load Balancing and Aggregation using Multilink PPP
  • Valid interfaces for Multilink devices
Before configuring Multilink PPP devices, you must configure your WAN interfaces and make the appropriate cabling connection for your needs. Refer to the hardware installation guide for your ImageStream product for information on making the WAN connection. See Chapter 7, Router Installation and Configuration Manual/Configuring a Synchronous Serial WAN Interface or the Command Reference for more detailed command descriptions and instructions.
After logging in, the main menu is displayed (your menu may look slightly different):
ISis-Router main menu 
1. Configuration menu 
2. Show interface status 
3. Advanced 
4. Router software management 
5. Backup/Restore 
6. halt/reboot 
0. Log off 
Select menu option 1, Configuration menu, and press Enter to configure the router. The Configuration menu should appear (your menu may look slightly different):
Configuration menu 
1. AAA (Password) Configuration 
2. Global configuration 
3. Network interface configuration 
4. Firewall and QOS configuration 
5. Service configuration 
6. Dynamic routing configuration 
7. Save configuration to flash 
0. ISis-Router main menu 
From the "Configuration menu", select menu option 3, Network interface configuration, and press Enter. This will open the ImageStream router's primary configuration file, wan.conf in the default editor. The wan.conf file is also accessible from the command line in the /usr/local/sand directory.

Configuring Load Balancing and Aggregation using Multilink PPP

"The Multilink interface for SAND devices allows multiple PPP encapsulated interfaces to be treated as a single logical interface. A Multilink device is a standard network device and may be configured in the same manner as all physical devices and subinterfaces. This link aggregation/load balancing software is compatible with Multilink PPP implementations on other manufacturer's routers. To use multilink PPP, all of the serial devices that you want to aggregate must run the PPP encapsulation, have the same endpoint and have MPPP configured on the remote router.
A Multilink device can:
  • aggregate multiple physical devices into a single logical device
  • aggregate physical devices of different speeds (i.e. T1 and DS3)
  • provide automatic, zero-downtime failover for multiple WAN devices interoperate with a Cisco router running MPPP
For compatibility with Cisco routers, the Cisco configuration must include the "ppp multilink interleave" command.
Aggregated links are controlled by a virtual Multilink interface configured in the interface configuration file. The interface is configured similarly to a Serial WAN interface. For this example, we will use this configuration showing two point-to-point T1 lines running PPP:
! 
interface Serial0 
 description Leased line to Mexico City 
 encapsulation ppp 
 ip address 25.0.0.1 255.255.255.252
!
interface Serial1
 #NOC phone: 800-555-1212 - Our account #58935 interface Serial1 
 description Leased line to Mexico City
 encapsulation ppp 
 ip address 25.0.0.5 255.255.255.252
!
In following example, we will bond Serial0 and Serial1 together. For the link aggregation to function, both Serial0 and Serial1 must terminate on the same remote router and the remote router must have MPPP configured.
The syntax of the Multilink interface command is:
interface Multilink XX

where XX is a device number. The location of a Multilink interface declaration in the interface configuration file is not important. By convention, the first Multilink device is Multilink1, though you may assign any number. You do not need to specify an encapsulation type or bandwidth, as both will be ignored. You must specify an ip address. A description field is optional.
In the example below, we have created a Multilink1 interface:
! 
interface Multilink1 
 description MPPP Port 
 ip address 216.146.78.1 255.255.255.252 
! 
To connect the Serial interfaces to the Multilink device that you have created, you must add two commands to each Serial interface. Use the ppp multilink keyword to indicate that the interface is part of a multilink PPP group. The syntax of the ppp multilink keyword is:
ppp multilink
The command accepts no parameters. To add the Serial device to the specific Multilink interface created in the previous step, use the multilink-group command.
The syntax of the ppp multilink keyword is:
multilink-group XX 
where XX is the device number you used when creating the Multilink interface. Using the original Serial interfaces and Multilink interface from above, the configuration below creates a multilink PPP group from the two individual PPP interfaces:
! 
interface Serial0 
description Leased line to Mexico City
encapsulation ppp 
ppp multilink  
multilink-group 1
!
#NOC phone: 800-555-1212 - Our account #58935 
interface Serial1 
description Leased line to Mexico City
encapsulation ppp 
ppp multilink 
multilink-group 1 
!
interface Multilink1
description MPPP Port
ip address 216.146.78.1 255.255.255.252
!
The Multilink interface appears as a regular interface in the router, meaning you can make modifications to the Multilink device configuration without taking down other interfaces. You can use firewalling, bandwidth limiting, rule-based routing and other advanced features of the router with any Multilink device you create. Like other interfaces, the bonder device is also available via SNMP for monitoring purposes.
The IP addresses on the individual T1s added to the Multilink device can be set to any valid IP address, and do not necessarily need to be identical. If you choose to use the same IP address on all of the individual PPP interfaces, you must use a host netmask (/32 or 255.255.255.255) on these devices.
Multilink PPP distributes the load evenly by fragmenting packets and sending the packet fragments down each T1 line before reassembling the packets at the remote end. Multilink interfaces automatically calculate bandwidth based on the active PPP interfaces in the group and will not attempt to use any interface which has hardware or protocol down.

Valid Interfaces for the Multilink device

The ppp multilink and multilink-group commands can only be used in conjunction with a Multilink device. You may only add SAND interfaces running PPP to Multilink devices.
Note: You must save the settings to the router's non-volatile flash memory! If the router is rebooted before saving, your changes will be lost! See Chapter 26, "Backup/Restore Menu: Managing Configurations" for more information.
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