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Example: Expanding an EX4200 Virtual Chassis in a Single Wiring Closet

A Virtual Chassis is a scalable switch composed of multiple interconnected EX4200 and EX4500 switches.

This example describes how to configure an expanding EX4200 Virtual Chassis within 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 EX4200-24P switch

  • One XFP uplink module

Before you begin, be sure you have confirmed that the existing EX4200 Virtual Chassis configuration is operating correctly. See Verifying That Virtual Chassis Ports Are Operational.

Overview and Topology

A Virtual Chassis configuration can be expanded without disrupting the site's network connectivity. This example describes adding a member switch to an existing Virtual Chassis configuration to provide additional access ports for connecting more PCs and Voice over IP (VoIP) phones at this location. You can continue to expand the Virtual Chassis configuration with additional members in the same wiring closet, using the same procedure. If you want to expand the Virtual Chassis configuration to include member switches in another wiring closet, see Example: Configuring an EX4200 Virtual Chassis Interconnected Across Multiple Wiring Closets.

If you want to retain the roles of the existing primary and backup switches, explicitly configure the primary-role priority of these switches, specifying the highest possible value (255) for both the primary and the backup.

During expansion, the existing Virtual Chassis configuration can remain powered on and connected to the network. Before powering up the new switch, interconnect it to the other switches using the dedicated VCPs on the rear panel. Do not run the EZSetup program on the added member switch.

This example shows an existing Virtual Chassis configuration composed of two EX4200 switches. The Virtual Chassis configuration is being expanded to include an EX4200-24P switch.


The topology for this example consists of:

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

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

  • One EX4200-24P switch (SWA-2) with 24 access ports, all of which support PoE

  • One uplink module with two 10-gigabit ports is installed in the EX4200-48P switch. These ports can be configured as trunk ports to connect to a distribution switch or customer edge (CE) router or as Virtual Chassis ports (VCPs) to interconnect with a member switch that is located too far for dedicated VCP cabling. (The uplink module ports on the SFP and SFP+ uplink modules and the SFP network interfaces on the EX4200-24F switches can also be used for these purposes.) For information on configuring the uplink ports as trunk ports to a distribution switch, see Configuring Gigabit Ethernet Interfaces (CLI Procedure). For information on configuring uplink ports as VCPs, see Setting an Uplink Port on an EX Series or QFX Series Switch as a Virtual Chassis Port.

Table 1 shows the configuration settings for the expanded Virtual Chassis.

Table 1: Components of the Expanded Virtual Chassis Access Switch
Member Switch Hardware Member ID Role in Virtual Chassis


EX4200-48P switch


primary; primary-role priority 255


EX4200-24T switch


backup; primary-role priority 255


EX4200-24P switch


linecard; primary-role priority 128

Figure 1 shows that the three member switches ( SWA-0, SWA-1 and SWA-2) 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: Expanded EX4200 Virtual Chassis in a Single Wiring ClosetExpanded EX4200 Virtual Chassis in a Single Wiring Closet


To expand a Virtual Chassis configuration to include additional member switches within a single wiring closet, perform these tasks:


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


CLI Quick Configuration

To maintain the primary and backup roles of the existing members and ensure that the new member switch functions in a linecard role, copy the following commands and paste them into the terminal window:

Step-by-Step Procedure

To ensure that the existing member switches retain their current roles and to add another member switch in a linecard role:

  1. Configure the primary-role priority of SWA-0 (member 0) to be the highest possible value, thereby ensuring that it functions as the primary of the expanded Virtual Chassis configuration.

  2. Configure the primary-role priority of SWA-1 (member 1) to be the highest possible value. This setting is recommended for high availability and smooth transition of primary role in case the original primary becomes unavailable.

  3. Interconnect the unpowered SWA-2 with SWA-0 using the dedicated VCPs on the rear panel. See Virtual Chassis Cabling Configuration Examples for EX4200 Switches for additional information.

  4. Power on SWA-2.

    You do not need to run EZSetup on SWA-2. The identification parameters that were set up for the primary apply implicitly to all members of the Virtual Chassis configuration. SWA-2 functions in a linecard role, because SWA-0 and SWA-1 have been configured to the highest primary-role priority values.

  5. Confirm SWA-2 is now included in the Virtual Chassis configuration by checking the front-panel LCD for the member ID of this switch.

  6. Cable the other VCP on SWA-2 to the Virtual Chassis.


    If you immediately cable both VCPs on SWA-2 into the existing Virtual Chassis, SWA-0 or SWA-1 might become nonoperational for several seconds. Network traffic to one of the switches is dropped during the downtime.

    The switch will return to the normal operational state with no user intervention, and normal operation of the Virtual Chassis will resume after this downtime.


To verify that the new switch has been added in the linecard role and that its VCPs are operational, perform these tasks:

Verifying That the New Switch Has Been Added in a Linecard Role


Verify that SWA-2 has been added in a linecard role to the Virtual Chassis configuration.


Use the show virtual-chassis command to list the member switches with their member IDs, primary-role priority values, and assigned roles.


The show virtual-chassis command lists the member switches of the Virtual Chassis configuration with the member IDs and primary-role priority values. It also displays the neighbor members with which each member is interconnected. This output shows that SWA-2 has been assigned member ID 2 and has the default primary-role priority value 128. Because the primary-role priority is lower than the primary-role priority of the other members, SWA-2 functions in the linecard role. You can continue to add more member switches, following the same procedure. It is possible to have multiple members in linecard roles with the same primary-role priority value.

Verifying That the VCPs Are Operational


Verify that the dedicated VCPs interconnecting the member switches are operational.


List the VCP interfaces on the Virtual Chassis configuration.


The show virtual-chassis vc-port all-members command lists all the interfaces for the Virtual Chassis configuration. In this case, no VCP uplinks have been configured. However, the VCP interfaces are automatically configured and enabled when you interconnect member switches using the dedicated VCPs. We recommend that you interconnect the member switches using both VCPs for redundancy. The VCP interfaces are identified simply as vcp-0 and vcp-1. The fpc number is the same as the member ID.


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

Troubleshooting Primary-role Priority


You want to designate a different member as the primary.


Change the primary-role priority value or values of the switches, designating the highest primary-role priority value for the switch that you want to be primary.

  1. Lower the primary-role priority of the existing primary (member 0).

  2. Set the primary-role priority of the member that you want to be the primary to the highest possible value (255):

Troubleshooting Nonoperational VCPs


The VCP interface shows a status of down.


Check the cable to make sure that it is properly and securely connected to the VCPs.