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Example: Configuring an EX4500 Virtual Chassis with a Primary and Backup in a Single Wiring Closet

A Virtual Chassis configuration is a scalable switch. You can provide secure, redundant network accessibility with a basic two-member EX4500 Virtual Chassis configuration and later expand the Virtual Chassis configuration to provide additional access ports as your office grows.

This example describes how to configure an EX4500 Virtual Chassis with a primary and backup in a single wiring closet:


This example uses the following hardware and software components:

  • Junos OS Release 11.1 or later for EX Series switches


    You must use Junos OS Release 11.4 or later if you are including three or more EX4500 switches in an EX4500 Virtual Chassis or a mixed EX4200 and EX4500 Virtual Chassis.

  • Two EX4500 switches with Virtual Chassis modules

Before you begin, be sure you have:

  1. Rack-mounted the switches. See Mounting an EX4500 Switch.

  2. Cabled the switches but not the Virtual Chassis ports (VCPs).

  3. Installed the same version of Junos OS Release 11.1 or later on both the switches

Overview and Topology

A Virtual Chassis configuration allows you to accommodate the networking needs of a growing office. The default configuration of a two-member Virtual Chassis includes a primary and a backup switch. In addition to providing more access ports than a single switch can provide, a Virtual Chassis configuration provides high availability through redundancy.

After you interconnect the switches using the dedicated VCPs and power on the switches, the VCPs are operational. The primary role priorities and member IDs are assigned by the software. The software elects a primary based on several criteria, including how long a member switch has belonged to the Virtual Chassis configuration. For additional details, see Understanding How the Primary in a Virtual Chassis Is Elected. Therefore, we recommend that you start by powering on only one member switch, the one that you want to function as the primary.


We recommend that you use the commit synchronize command to save any configuration changes that you make to a Virtual Chassis.

The Virtual Chassis configuration provides networking access for onsite workers who are sitting within the range of a single wiring closet. The workers all use personal computers and VoIP phones. As the office grows, you can add EX4200 switches to meet increased needs for access ports.


The topology for this example consists of two EX4500 switches.

Table 1 shows the default configuration settings for the two-member Virtual Chassis.

Table 1: Components of the Basic Virtual Chassis Access Switch Topology
Member Switch Hardware Member ID Role and Priority


EX4500 switch


Primary: primary-role priority 128


EX4500 switch


Backup: primary-role priority 128

Figure 1 shows that switches SWA-0 and SWA-1 are interconnected with their dedicated VCPs on the rear panel. The LCD on the front displays the member ID and role.

Figure 1: Basic EX4500 Virtual Chassis with Primary and BackupBasic EX4500 Virtual Chassis with Primary and Backup


Configure a Virtual Chassis with a default primary and backup in a single wiring closet:


Step-by-Step Procedure

To configure a Virtual Chassis with primary and backup:

  1. Power on SWA-0 (the member switch that you want to function as the primary).

  2. Power on SWA-1 (the member switch that you want to function as the backup).

  3. Set the PIC mode to Virtual Chassis mode on both switches:

  4. Run the EZSetup program on SWA-0, specifying the identification parameters. See Connecting and Configuring an EX Series Switch (CLI Procedure) for details.

  5. Cable the Virtual Chassis member switches together.

  6. (Optional) Configure SWA-0 with the virtual management Ethernet (VME) interface for out-of-band management of the Virtual Chassis configuration, if desired:

  7. (Optional, but recommended) Disable the split and merge feature:


To confirm that the Virtual Chassis configuration is operational, perform these tasks:

Verifying That the Primary-role Priority Is Assigned Appropriately


Verify that the primary, which has been selected by default, is the member switch that you want to function in that role.


  1. Check the front-panel LCD to confirm that the switch has powered on correctly and that a member ID has been assigned.

  2. List the member switches of the Virtual Chassis configuration.


The show virtual-chassis command lists the member switches interconnected in a Virtual Chassis configuration with the member IDs that have been assigned by the primary, the primary-role priority values, and the roles. It also displays the neighbor members with which each member is interconnected. The output shows that SWA-0, member 0, has been assigned default primary-role priority 128. Because SWA-0 is the first member to be powered on, it has the most seniority and is therefore assigned the role of primary. SWA-1 is powered on after member 0, so it is assigned the role of backup. The member IDs are displayed on the front panel of the switches. Check and confirm whether the default assignment is satisfactory.

Verifying That the VCPs Are Operational


Verify that the dedicated VCPs interconnecting the switches are operational.


Display the VCPs of all the members:


The show virtual-chassis command lists the interfaces that are enabled for the member switches of the Virtual Chassis configuration and shows the status of the interfaces. The output in this example shows that two of the VCPs are operational. A single cable has been used to interconnect vcp-0 of member ID 0 and vcp-0 of member ID 1. That interconnection is sufficient for the switch to be operational. However, we recommend that you connect the second set of VCPs for redundancy.

Troubleshooting the Virtual Chassis

To troubleshoot the configuration of a Virtual Chassis, perform these tasks:

Troubleshooting the Assignment of Roles


The primary and backup roles are not assigned to the member switches that you want to function in these roles.


Modify the primary-role priority values.

To quickly modify the primary-role priority of SWA-1 (member ID 1), copy the following command and paste it into the switch terminal window:

Troubleshooting the VCPs


The VCPs are down.


  1. Check to make sure that you have cabled the appropriate ports.

  2. Check to make sure that the cables are seated properly.

We recommend that you interconnect both of the VCPs on the member switches, for redundancy and high availability.