Multilink PPP cont

R4(config-if)# ppp multilink

Activates the interface for Multilink PPP operation

R4(config-if)# dialer load-threshold 128 outbound

Allows additional B-Channels to be added to the Multilink PPP bundle once the current bandwidth utilization reaches 50% in the outbound direction

© 2001, Cisco Systems, Inc. All rights rieserived. Cisco CCIE Prep v1.0—Module 3-40

The command ppp multilink activates the interface for MPPP operation and allows negotiation of Multilink PPP at connect time, thus establishing a single-channel MPPP bundle. However, this command alone is not sufficient enough to take advantage of the fragmentation, load balancing, or bandwidth-on-demand features of the Multilink PPP.

The dialer load-threshold load command sets the point at which additional B channels will be added to the MPPP bundle. When the total load of all "up" B channels (n) is greater than the load threshold, the dialer interface (in this case, BRI 0/0) adds an extra channel to the multilink bundle. In a similar way, if the total load for all the "up" B channels minus one (n - l) is at or below the threshold, the additional channels will be taken back down.

The load argument is the average load for the interface; it is a value from 1 (unloaded) to 255 (fully loaded). As shown in the above example a 50% load threshold is achieved by configuring the "load" argument with a value of l28. The load argument is expressed as a percentage n/255 where n is the value configured.

The outbound argument sets the load calculation to be made only on outbound traffic. The inbound argument does the same, but for inbound traffic only. Using the either argument sets the load as the larger of the outbound and inbound loads.

Adding MPPP Channels More Quickly

R4 (config-if)# load-interval value-in-aeconda

• Increases the frequency of interface load calculation

R4 (config-if)# ppp timeout multilink link add 3 value-in-aeconda

• Sets the time required to add another link to the Multilink


© 2001 Cis

o Systems, Inc. All riights reserved. Cisco CCIE Prep v1.0—Module 3-48

On a Primary Rate Interface (PRI) ISDN circuit, it is often desirable to add additional B channels as quickly as possible. If Multilink Point-to-Point Protocol (MPPP) is configured on the PRI interface, the following commands allow you to add B channels to the Multilink bundle more quickly:

R4(config-if)# load-interval 30

This command increases the frequency of the interface load calculation. By default, the interface load is calculated as an exponential average over the last five minutes. By setting the "load-interval" parameter to 30 seconds, you force a more frequent calculation of the interface load. This results in an earlier detection of changes in the interface load. By shortening the length of time during which you compute the interface load, you also shorten the time required to bring up additional B channels because the router will detect an increase of the interface load sooner.

R4(config-if)# ppp timeout multilink link add 3

This command sets the time required to add another link to the multilink bundle. This timer determines how long PPP multilink waits after adding a link to the bundle before adding additional links due to the load threshold being exceeded. The minimum possible value is 1 second. The default is 30 seconds.

Note These commands are also useful for testing Multilink PPP on BRI interfaces. These commands will reduce the time required to see if Multilink PPP is working properly. Timesaving tips like these can be extremely helpful in the CCIE Lab.

PPP Callback

PPP callback provides a client-server relationship between the end points of a point-to-point connection. PPP callback allows a router to request that a peer router call back.

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