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Achieving Greater Bandwidth, Load Balancing, and Redundancy with Multilink Bundles


The topics below discuss the overview of MLPPP Bundles and Link Fragmentation and Interleaving (LFI) on Serial Links, and configuring an MLPP bundle on security devices.

Juniper Networks devices support MLPPP and MLFR multilink encapsulations. MLPPP multilink encapsulation enables you to bundle multiple PPP links into a single multilink bundle and MLFR multilink encapsulation enables you to bundle multiple Frame Relay data-link connection identifiers (DLCIs) into a single multilink bundle. Multilink bundles provide additional bandwidth, load balancing, and redundancy by aggregating low-speed links, such as T1, E1, and serial links.


Currently, Junos OS supports bundling of only one xDSL link under bundle interface.

You configure multilink bundles as logical units or channels on the link services interface lsq-0/0/0:

  • With MLPPP and MLFR FRF.15, multilink bundles are configured as logical units on lsq-0/0/0—for example, lsq-0/0/0.0 and lsq-0/0/0.1.

  • With MLFR FRF.16, multilink bundles are configured as channels on lsq-0/0/0—for example, lsq-0/0/0:0 and lsq-0/0/0:1.

After creating multilink bundles, you add constituent links to the bundle. The constituent links are the low-speed physical links that are to be aggregated. You can create 64 multilink bundles, and on each multilink bundle you can add up to 8 constituent links. The following rules apply when you add constituent links to a multilink bundle:

  • On each multilink bundle, add only interfaces of the same type. For example, you can add either T1 or E1, but not both.

  • Only interfaces with a PPP encapsulation can be added to an MLPPP bundle, and only interfaces with a Frame Relay encapsulation can be added to an MLFR bundle.

  • If an interface is a member of an existing bundle and you add it to a new bundle, the interface is automatically deleted from the existing bundle and added to the new bundle.

Configuring a multilink bundle on the two serial links increases the bandwidth by 70  percent from approximately 1 Mbps to 1.7 Mbps and prepends each packet with a multilink header as specified in the FRF.12 standard. To increase the bandwidth further, you can add up to eight serial links to the bundle. In addition to a higher bandwidth, configuring the multilink bundle provides load balancing and redundancy. If one of the serial links fails, traffic continues to be transmitted on the other links without any interruption. In contrast, independent links require routing policies for load balancing and redundancy. Independent links also require IP addresses for each link as opposed to one IP address for the bundle. In the routing table, the multilink bundle is represented as a single interface.

Example: Configuring an MLPPP Bundle

This example shows how to configure an MLPPP bundle to increase traffic bandwidth.


Before you begin, you should have two Juniper Networks devices configured with at least two serial interfaces that communicate over serial links.


In this example, you create the MLPPP bundle lsq-0/0/0.0 at the logical unit level of the link services interface lsq-0/0/0 on Juniper Networks devices R0 and R1. You then add the two serial interfaces se-1/0/0 and se-1/0/1 as constituent links to the multilink bundle. In Figure 1, your company's branch office is connected to its main branch using devices R0 and R1. You transmit data and voice traffic on two low-speed 1-Mbps serial links. To increase bandwidth, you configure MLPPP and join the two serial links se-1/0/0 and se-1/0/1 into the multilink bundle lsq-0/0/0.0. Then you configure LFI and CoS on R0 and R1 to enable them to transmit voice packets ahead of data packets.

Figure 1: Configuring MLPPP and LFI on Serial Links
Configuring MLPPP and LFI
on Serial Links


CLI Quick Configuration

To quickly configure this example, copy the following command, paste it into a text file, remove any line breaks, change any details necessary to match your network configuration, copy and paste the command into the CLI at the [edit] hierarchy level, and then enter commit from configuration mode.

Step-by-Step Procedure

The following example requires you to navigate various levels in the configuration hierarchy. For instructions on how to do that, see Using the CLI Editor in Configuration Mode.

To configure MLPPP bundle:

  1. Create an interface on both devices.
  2. Configure a family inet and define the IP address on device R0.
  3. Configure a family inet and define the IP address on device R1.
  4. Specify the names of the constituent links to be added to the multilink bundle on both devices.
  5. Set the serial options to the same values for both interfaces on R0.Note

    R0 is set as a DCE device. The serial options are not set for interfaces on R1. You can set the serial options according to your network setup.


From configuration mode, confirm your configuration by entering the show interfaces lsq-0/0/0, show interfaces se-1/0/0, and show interfaces se-1/0/1 commands for R0 and R1. If the output does not display the intended configuration, repeat the configuration instructions in this example to correct it.

If you are done configuring the device, enter commit from configuration mode.


Confirm that the configuration is working properly.

Verifying the MLPPP Bundle


Verify that the constituent links are added to the bundle correctly.


From operational mode, enter the show interfaces lsq-0/0/0 statistics command.