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Example: Configuring an EX4200 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 EX4200 Virtual Chassis and later expand the Virtual Chassis configuration to provide additional access ports as your office grows.

This example describes how to configure an EX4200 Virtual Chassis with a primary and backup in a single wiring closet:


This example uses the following hardware and software components:

  • Junos OS Release 9.0 or later for EX Series switches

  • One EX4200-48P switch

  • One EX4200-24T switch

  • One XFP uplink module

Before you begin, be sure you have:

  1. Rack-mounted the switches.

  2. Installed the uplink module. See Installing an Uplink Module in an EX4200 Switch.

  3. Cabled the switches. See Connecting a Virtual Chassis Cable to an EX4200 Switch.

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.

This example shows a Virtual Chassis configuration composed of two EX4200 switches. One of the switches has an uplink module with ports that can be configured to connect to a distribution switch or customer edge (CE) router or that can be configured as Virtual Chassis ports (VCPs) to interconnect with a member switch that is located too far for the dedicated VCP cabling. (The network interfaces on EX4200-24F switches can also be configured as VCPs.) For information on configuring the uplink ports as trunk ports to a distribution switch, see Configuring Gigabit Ethernet Interfaces (CLI Procedure). For an example of configuring uplink ports as VCPs, see Setting an Uplink Port on an EX Series or QFX Series Switch as a Virtual Chassis Port.

By default, after you interconnect the switches with 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 multimember Virtual Chassis.

The Virtual Chassis configuration provides networking access for 50 onsite workers, who are sitting within range of a single wiring closet. The workers all use personal computers and VoIP phones. As the office grows, you can add more EX4200 switches to meet increased needs for access ports.


The topology for this example consists of two switches, one of which contains an uplink module:

  • One EX4200-48P switch (SWA-0) with 48 access ports, all of which support PoE

  • One EX4200-24T switch (SWA-1) with 24 access ports, including eight ports that support PoE

  • One XFP uplink module, with two 10–Gigabit Ethernet ports, is installed in the EX4200-48P switch

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


EX4200-48P switch


Primary: primary-role priority 128


EX4200-24T switch


Backup: primary-role priority 128

Figure 1 shows that 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. SWA-0 also includes an uplink module. Its uplink ports can be used to connect to a distribution switch.

Figure 1: Basic EX4200 Virtual Chassis with Primary and BackupBasic EX4200 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. Make sure the VCPs on the rear panel of the member switches are properly cabled. See Virtual Chassis Cabling Configuration Examples for EX4200 Switches.

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

  3. Check the front-panel LCD to confirm that the switch has powered on correctly.

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

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

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

  7. Power on SWA-1.


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 vc-port 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 and two VCPs are not. 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.

You should generally cable and interconnect both of the VCPs on the member switches, for redundancy and high availability.