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Primary-role Election in a Virtual Chassis

In a two-member MX Series or EX9200 Virtual Chassis, either member device can be elected as the primary device (also known as the protocol primary, or VC-P) of the Virtual Chassis. The first member device to join the Virtual Chassis becomes the initial primary device by default. After the Virtual Chassis is formed with both member devices, the Virtual Chassis Control Protocol (VCCP) software runs a primary-role election algorithm to elect the primary device for the Virtual Chassis configuration.

If the primary device in a Virtual Chassis fails, the backup device (also known as the protocol backup, or VC-B) takes over the primary role of the Virtual Chassis. You can also switch the global roles of the primary device and backup device in a Virtual Chassis by issuing the request virtual-chassis routing-engine master switch command.

Note:

You cannot configure primary-role election for an MX Series or EX9200 Virtual Chassis in the current release.

The VCCP software uses the following algorithm to elect the primary device for an EX9200 or MX Series Virtual Chassis:

  1. Choose the member device that has the highest value for the internal primary-role election flag.

    The primary-role election algorithm uses an internal flag that keeps track of the member state for the purpose of electing the Virtual Chassis primary device. In most cases, VCCP elects the member device with the higher flag value over the member device with the lower flag value as the protocol primary.

    To display the primary-role election flag value, issue the show virtual-chassis protocol database extensive command. The flag value used for primary-role election appears in the TLVs field of the command output, as shown in the following example:

  2. Choose the member device with the highest primary-role priority value.

    The primary-role priority value is assigned to the member device by the VCCP software, and is not configurable in the current release. The primary-role priority value can be one of the following:

    • 129—The routing-engine role is assigned to the member device.

    • 128—No role is assigned to the member device.

    • 0—The line-card role is assigned to the member device (not supported in the current release).

    To display the primary-role priority value for the member devices in the Virtual Chassis, issue the show virtual-chassis status command.

  3. Choose the member device that is active in the Virtual Chassis.

  4. Choose the member device that belongs to the Virtual Chassis with the largest number of members.

    Note:

    This criterion is not used in the current release because all EX9200 and MX Series Virtual Chassis configurations have two member devices.

  5. Choose the member device that is the accepted (elected) protocol primary of the Virtual Chassis.

  6. Choose the member device that is the current protocol primary (VC-P) of the same Virtual Chassis.

  7. Choose the member device that is the current protocol backup (VC-B) of the same Virtual Chassis.

  8. Choose the member device that has been part of the Virtual Chassis configuration for the longest period of time.

  9. Choose the member device that was the previous protocol primary of the same Virtual Chassis.

  10. Choose the member device with the lowest media access control (MAC) address.

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