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Understanding How the Master in a Virtual Chassis Is Elected
 | Note: This topic applies does not apply to EX8200 Virtual Chassis. See EX8200 Virtual Chassis Overview. |
All switches that are interconnected in a Virtual Chassis configuration are member switches of that Virtual Chassis. Each Virtual Chassis configuration has one member that functions as the master and controls the Virtual Chassis configuration.
When a Virtual Chassis configuration boots, the Juniper Networks Junos operating system (Junos OS) on the switches automatically runs a master election algorithm to determine which member switch assumes the role of master.
The algorithm proceeds from the top condition downward until the stated condition is satisfied:
- Choose the member with the highest user-configured mastership priority (255 is the highest possible value). A switch with a mastership priority of 0 will always stay in the linecard role.
- Choose the member that was master the last time the Virtual Chassis configuration booted.
- Choose the member that has been included in the Virtual Chassis configuration for the longest period of time. (For this to be a deciding factor, there has to be a minimum time lapse of 1 minute between the power-ons of the individual interconnected member switches.)
- Choose the member with the lowest MAC address.
The variations among switches and switch models do not impact the master election algorithm.
To ensure that a specific member is elected as the master:
- Power on only the switch that you want to configure as master of the Virtual Chassis configuration.
- Configure the mastership priority of that member to have the highest possible value (255).
- Continue to configure other members through the master member.
- Power on the other members.
You can also specify the switch roles by preprovisioning your Virtual Chassis. Preprovisioning a Virtual Chassis allows you to manually assign the member ID and role for each switch in the Virtual Chassis. See Configuring an EX3300 Virtual Chassis (CLI Procedure), Configuring an EX4200, EX4500, or EX4550 Virtual Chassis (CLI Procedure), or Configuring a QFX Series Virtual Chassis (CLI Procedure).
