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Example: Expanding an EX3300 Virtual Chassis

An EX3300 Virtual Chassis is a scalable switch composed of multiple interconnected EX3300 switches.

This example describes how to configure an expanding EX3300 Virtual Chassis within a single wiring closet. The process, however, would be identical if you were connecting EX3300 member switches in different wiring closets:


This example uses the following hardware and software components:

  • Junos OS Release 11.3 or later for EX Series switches

  • Three EX3300 switches

Before you begin, be sure you have confirmed that the existing EX3300 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 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 default VCP uplink ports on the front panel. Do not run the EZSetup program on the added member switch.

This example shows an existing Virtual Chassis configuration composed of two EX3300 switches. The Virtual Chassis configuration is being expanded to include an additional EX3300 switch.


The topology for this example consists of three EX3300 switches.

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


EX3300 switch


primary; primary-role priority 255


EX3300 switch


backup; primary-role priority 255


EX3300 switch


linecard; primary-role priority 128


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 default VCPs on the front panel. See Virtual Chassis Cabling Configuration Examples for EX3300 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 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 VCPs have been configured. However, the VCPs are automatically configured and enabled when you interconnect member switches using the default VCP uplink ports. 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.