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The EX4200 in a Virtual Chassis (VC) has specific member roles defined by configuration or VC election process

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Knowledge Base ID: KB10967
Last Updated: 08 Dec 2010
Version: 4.0

Summary:
A Virtual Chassis(VC) is a collection of interconnected EX4200 switches that are managed as a single switch. A virtual chassis consists of two to ten individual EX4200 switches known as member switches and each member switch has its own roles and responsibilities.

Problem or Goal:
 

Solution:
There are 3 types of switches on VC environment and each type of switch has the following roles and responsibilities.
  • Master Role
The member that functions in the master role:
Manages the member switches.
Runs Juniper Networks Junos operating system (Junos OS) for Juniper Networks EX Series Ethernet Switches in a master role.
Runs the chassis management processes and control protocols.
Represents all the member switches interconnected within the Virtual Chassis configuration. (The hostname and other properties that you assign to this switch during setup apply to all members of the Virtual Chassis configuration.)

When an EX4200 switch is powered on as a standalone switch, it is considered the master member. In a multimember Virtual Chassis configuration, one member functions as the master and a second member functions as the backup:
In a preprovisioned configuration, one of the two members assigned as routing-engine functions as the master member. The selection of which member assigned as routing-engine functions as master and which as backup is determined by the software based on the master election algorithm. See Understanding How the Master in a Virtual Chassis Configuration Is Elected.
In a configuration that is not preprovisioned, the selection of the master and backup is determined by the mastership priority value and secondary factors in the master election algorithm.
  • Backup Role
The member that functions in the backup role:
Maintains a state of readiness to take over the master role if the master fails.
Runs Junos OS for EX Series switches in a backup role.
Synchronizes with the master in terms of protocol states, forwarding tables, and so forth, so that it is prepared to preserve routing information and maintain network connectivity without disruption in case the master is unavailable.

You must have at least two member switches in a Virtual Chassis configuration in order to have a backup member.
In a preprovisioned configuration, one of the two members assigned as routing-engine functions in the backup role. The selection of which member assigned as routing-engine functions as master and which as backup is determined by the software based on the master election algorithm. See Understanding How the Master in a Virtual Chassis Configuration Is Elected.
In a configuration that is not preprovisioned, the selection of the master and backup is determined by the mastership priority value and secondary factors in the master election algorithm.
  • Linecard Role
A member that functions in the linecard role:
Runs only a subset of Junos OS for EX Series switches.
Does not run the chassis control protocols.
Can detect certain error conditions (such as an unplugged cable) on any interfaces that have been configured on it through the master.

A Virtual Chassis configuration must have at least three members in order to include a linecard member.
In a preprovisioned configuration, you can explicitly configure a member with the role of linecard, which makes it ineligible for functioning as a master or backup.
In a configuration that is not preprovisioned, the members that are not selected as master or backup function as linecard members of the Virtual Chassis configuration. The selection of the master and backup is determined by the mastership priority value and secondary factors in the master election algorithm.

Purpose:
Specifications

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