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How to configure link aggregation or bonding on the Kemp LoadMaster

The LoadMaster has the ability to bond its interfaces together to provide for additional throughput as well as redundancy. The LoadMaster supports two styles of bonding: 802.3ad and Active-Backup.

Before creating a bonded interface please note the following:

  • You can only bond interfaces higher than the parent, so if you choose to start with port 10 then you can only add ports 11 and greater
  • Bond links first. If you need VLAN tagging, add VLANs after the bond has been configured
  • In order to add a link to a bonded interface, any IP addressing must first be removed from the link to be added
  • Enabling the Active-Backup mode generally does not require switch intervention
  • Bonding eth0 with eth1 can lead to serious issues and is not allowed to occur

To configure an interface for use with bonding, follow the steps below in the LoadMaster Web User Interface (WUI):

  1. In the main menu, select System Configuration.
  2. Select the lowest indexed interface you want to use, for example eth0.
  3. Click the Interface Bonding button.
  4. Click Create a bonded interface.

          This will turn eth* to bnd*.

  1. In the main menu, select System Configuration and bnd*.
  2. Configure the addressing as needed.
  3. To add interfaces or to modify the bond type click Bonded Devices.
  4. You can select the style of bonding in the Bonding mode drop-down list:


  • 802.3ad – True bonding which aggregates the bandwidth of multiple interfaces. Both interfaces must connect to the same switch and the switch ports must be configured to support this.
  • Active-backup – This style of bonding allows for link redundancy but does not aggregate the bonded interfaces. Each link can be connected to a different switch for full redundancy. No switch configuration is required for this.

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Gerardo Castro

The mode we need to configure is Active-Backup



Pascal Jolin

In regards to this:
"Bonding eth0 with eth1 can lead to serious issues and is not allowed to occur"

Why is this? Is this a technical problem with the load balancer, or just a "dumb users that don't know what they're doing shouldn't do this"?

The LM3000 has 4 ports total. Our goal when we acquired them was to create one LACP bond across all 4 ports, and the connect 2 ports to each of 2 switches in a stack, for maximum redundancy and bandwidth.

But with this rule, we're stuck doing this with only 3 ports, leaving one unused port -- or to split in two groups of 2 ports (eth0+eth2, eth1+eth3), which is less than satisfactory from a redundancy / bandwidth optimisation point of view.



Justin Federico


Thank you for your comment. The bonding of eth0 and eth1 is not an available option in the webUI. This is due to the fact that eth1 has certain capabilities regarding HA that can cause conflicts if this interface is bonded to eth0. This is the only scenario where the conflict can occurs as a bond can be created on eth1 and have any (higher) interface added to it without issue.

In an HA configuration, eth1 will act as a direct connect interface by which the LM's can exchange HA updates without the need for an IP on the interface. Bonding eth0 and eth1 could trigger this functionality, when it would not be wanted, leading to unknown results.

Your comment has sparked an internal discussion and I am going to have this limitation revisited by our development team.