Multilink

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Contents

Introduction

Multilink interfaces simply take two or more physical interfaces and make a logical connection out of them. For example, two T1s can be tied together into a single three Mbps interfaces.

Requirements

Multilink interfaces require a minimum of two physical lines. In addition, the telco must support multilink as well. For testing purposes, two Imagestream routers can be configured back to back.

PPP Configuration

Basic configuration for the physical interfaces is the same, define the clock and encapsulation. ppp multilink enables multilink, and multilink-group 1 assigns the interface to a multilink group. After defining physical interfaces, configure a virtual interface to actually work with.

Side 1: Normal customer side

!
interface Serial1
 service-module t1 clock source line
 encapsulation ppp
 ppp multilink
 multilink-group 1
!
interface Serial2
 service-module t1 clock source line
 encapsulation ppp
 ppp multilink
 multilink-group 1
!
interface Multilink1
 ip address 192.168.4.2 255.255.255.252
!
The two interfaces are configured as bare ppp. Turn on multilink, and assign each one to a group. Then create an interface MultilinkX, where X is the group assigned to the physical interfaces.

Side 2: Testing side ( pseudo telco )

!
interface Serial1
 service-module t1 clock source internal
 encapsulation ppp
 ppp multilink
 multilink-group 1
!
interface Serial2
 service-module t1 clock source internal
 encapsulation ppp
 ppp multilink
 multilink-group 1
!
interface Multilink1
 ip address 192.168.4.1 255.255.255.252
!
service-module t1 clock source internal is the primary difference between Side 1 and Side 2. Normally the interface gets its clock timing from the line(telco) but in back to back setups, one side must generate the clock signal on the line.

Multilink Frame

Multilink Frame requires only encapsulation frame-relay MFRX where X is a non-negative integer. The MFRX interface is then configured as a normal physical frame relay device. All physical interfaces with MFRX configured as the encapsulation are then added to that multilink group.

Side 1: Normal customer side

!
interface Serial3
 encapsulation frame-relay MFR1
!
interface Serial4
 encapsulation frame-relay MFR1
!
interface MFR1
 encapsulation frame-relay
!
interface MFR1.1
 encapsulation frame-relay ietf
 frame-relay interface-dlci 591
 ip address 192.168.5.2 255.255.255.252
!
Set the encapsulation on the physical interfaces to MFR1. Then configure MFR1 as a frame-relay device. Configure MFR1.1 as a frame relay sub-interface with a DLCI of 591.

Side 2: Testing side ( pseudo telco )

!
interface Serial3
 encapsulation frame-relay MFR1
!
interface Serial4
 encapsulation frame-relay MFR1
!
interface MFR1
 encapsulation frame-relay
 frame-relay mode dce
!
interface MFR1.1
 encapsulation frame-relay ietf
 frame-relay interface-dlci 591
 ip address 192.168.5.1 255.255.255.252
!
When operating back to back, one side must have frame-relay mode dce. This tells the interface to act as the telco side of the line.

Configuration Option Reference

bandwidth {bits_per_second}

Description

Sets the intended bandwidth in bits per second. This command does not set internal clock speeds. See baud to set internal clocking for interfaces.
When used in conjunction with ATM QoS commands this value is used to calculate the correct ATM QoS settings. When this command is used on a Frame-relay interface this is used to setup rate-limiting on the interface.

Parameter

bits_per_second - Non-negative integer which represents how much data an interface can push.

Examples

bandwidth 2000000 - Sets the interface to 2 Mbps
bandwidth 100000000 - Sets the interface to 100Mbps

description string

Description

Used to add a comment (description) for tracking what is attached to a particular interface.

Parameter

string - Any alpha-numeric characters are allowed.

Example

description Link to CO - Documents this interface as connecting to CO

encapsulation {frame-relay|hdlc|none|ppp|raw|x25|atm|aal5snap|aal5autoppp}

Description

Set the protocol for a serial interface.

Parameters

frame-relay - Frame Relay protocol (Uses IETF standard)
hdlc - High-Level Data Link Control (HDLC) protocol for serial interface. This encapsulation method provides the synchronous framing and error detection functions of HDLC without windowing or retransmission
none - Raw character device read/write for external applications
ppp - Point-to-Point Protocol
raw - Raw IP encapsulation
x25 - X.25 protocol
atm - ATM VC multiplex encapsulation
aal5snap - ATM Aal5snap encapsulation (valid only on an atm sub-interface)
aal5autoppp - ATM Aalautoppp encapsulation (valid only on an atm sub-interface)

Examples

encapsulation frame-relay - Set the protocol on the interface to frame-relay.
encapsulation raw - No protocol, an external program will process the raw data from the line.

ip address IPv4_Address IPv4_Netmask [secondary]

Description

To set IP addresses for an interface, use the ip address command.

Parameters

IPv4_Address - Series of four numbers, 0 to 255, separated by periods. For more information see the Wikipedia
IPv4_Netmask - Four integers from zero to 255 separated by periods
secondary - Specifies additional IP addresses (aliases)

Examples

ip address 10.1.1.199 255.0.0.0 - Assigns the interface the IP address 10.1.1.199 with a Class A network mask
ip address 192.168.1.254 255.255.255.0 secondary - Assigns the interface the alias IP address 192.168.1.254 with a Class C network mask

frame-relay interface-dlci <DLCI>

Description

Set the DLCI number of the frame relay link. Normally your DLCI is provided by telco, in a back to back or testing setup, any positive integer can be used.

Parameter

<DLCI> - Identifying number assigned by telco

Examples

frame-relay interface-dlci 50 - Associate DLCI 50 to this interface.

ppp multilink

Description

Enables multilink on a device using the PPP protocol.

ppp multilink fragmentation {enabled|disabled}

Description

Parameters

enabled - Turn on the feature(Default)
disabled - Turn off the feature

Examples

ppp multilink fragmentation disabled - Turns off multilink fragmentation ( Common when dealing with Cisco routers )

multilink-group group_id

Description

Sets the group number of the multilink device, this number names the multilink interface which binds the group together. i.e. group 1 would be bound to Multilink1

Parameter

group_id - Identifies the multilink group this interface is part of.

Examples

multilink-group 3 - Assigns the interface to group 3

service-module t1 clock source <line | internal>

Description

Set the clock clock or line sync for an interface

Parameter

line - Set the interface to sync from the line.
internal - Set the interface to generate sync on the line.

Example

service-module t1 clock source internal - Sets the internal CSU/DSU to generate clock signal for the connection
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