Enable Jumbo Frames on the VM-Series Firewall

By default, the maximum transmission unit (MTU) size for packets sent on a Layer 3 interface is 1500 bytes. This size can be manually set to any size from 512 to 1500 bytes on a per-interface basis. Some configurations require Ethernet frames with an MTU value greater than 1500 bytes. These are called jumbo frames.
To use jumbo frames on a firewall you must specifically enable jumbo frames at the global level. When this is enabled, the default MTU size for all Layer 3 interfaces is set to a value of 9192 bytes. This default value can then be set to any value in the range of 512 to 9216 bytes.
After setting a global jumbo frame size it becomes the default value for all Layer 3 interfaces that have not explicitly had an MTU value set at the interface configuration level. This can become a problem if you only want to exchange jumbo frames on some interfaces. In these situations, you must set the MTU value at every Layer 3 interface that you do not want to use the default value.
The following procedure describes how to enable jumbo frames on a firewall, set the default MTU value for all Layer 3 interfaces and to then set a different value for a specific interface.
  1. Enable jumbo frames and set a default global MTU value.
    1. Select DeviceSetupSession and edit the Session Settings section.
    2. Select Enable Jumbo Frame.
    3. Enter a value for Global MTU.
      The default value is 9192. The range of acceptable values is: 512 - 9216.
    4. Click OK.
      A message is displayed that informs you that enabling or disabling Jumbo Frame mode requires a reboot and that Layer 3 interfaces inherit the Global MTU value.
    5. Click Yes.
      A message is displayed to inform you that Jumbo Frame support has been enabled and reminds you that a device reboot is required for this change to be activated.
    6. Click OK.
    7. Click Commit.
  2. Set the MTU value for a Layer 3 interface and reboot the firewall.
    The value set for the interface overrides the global MTU value.
    1. Select NetworkInterfaces.
    2. Select an interface of the Layer3 Interface type.
    3. Select AdvancedOther Info.
    4. Enter a value for MTU.
      The default value is 9192. The range of acceptable values is: 512 - 9216.
    5. Click OK.
    6. Click Commit.
    7. Select DeviceSetupOperations and select Reboot Device.

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