This article provides step by step procedure in electing a specific member as Master/Primary in a VC.

The primary-role election algorithm does not consider the different switch models or platforms in the Virtual Chassis. For some Virtual Chassis that can contain different types of switches, it is recommended to configure certain switches in the primary and backup Routing Engine roles. 

To make sure a specific member is elected as the primary:

1. Power on only the switch that you want to be the primary in the Virtual Chassis.

2. (For a non-provisioned Virtual Chassis) Manually configure the primary-role priorities as follows:

   1. Configure the highest possible primary-role priority value (255) on the member from the first step.

   2. On the same member, which is now the primary, configure priority values on the other members. (For example, use the same value or next-highest value on the member you want to be the backup, and lower values on the other members.)

3. (For a preprovisioned Virtual Chassis) Configure the Routing Engine role on the two members that you want to act as the primary and backup members. (You can also explicitly configure the remaining members into the line-card role.)

4. Power on the other members.

For more details on VC Mastership election, refer the article: KB82346 [juniper.net]