How a MAC address change affects the LoadMaster

In our Installation Guides we recommend the Media Access Control (MAC) address of all Network Interface Cards (NICs) to be set to static. This article explains why and what a dynamically set MAC address could cause.

The KEMP licence is created from the VLM's access code and the access code is based on the host’s MAC address. If the MAC address of the VLM NICs are changed, this changes the access code and as a result the LoadMaster license is invalid.

If the MAC changes, the network setting for eth0 is reset, causing a loss of access, which includes causing the Web User Interface (WUI) to be inaccessible, production traffic to be impacted, and High Availability (HA) clusters to break and the license to be reset.

If you encountered this issue, you should set the MAC address back or contact Kemp Support for assistance.

To prevent Virtual LoadMaster (VLM) license issues due to MAC address changes, ensure that the MAC address of the VLM is set statically.

Refer to the relevant section below to find out what steps should be taken to set a static MAC address for VLMs which are deployed on VMware ESX and Hyper-V.  

VMware ESX

  1. Locate a virtual machine in the vSphere Web Client.
  2. Right-click the virtual machine and select Edit Settings.
  3. On the Hardware tab, select the network adapter.
  4. In the MAC Address section, select Manual from the drop-down menu.
  5. Type the static MAC address and click OK.


  1. In the Hyper-V Manager, right-click the VLM and select Settings.
  2. Expand the first network adapter listed.
  3. Click Advanced Features.
  4. Under MAC Address, select the Static radio button.
  5. Click OK to save the settings.

For more information, refer to the vendor-specific Installation Guides.

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