Technical Documentation

Example: Expanding a Virtual Chassis Configuration in a Single Wiring Closet

A Virtual Chassis configuration is a scalable switch composed of multiple interconnected EX4200 switches. Up to ten EX4200 switches can be interconnected as a Virtual Chassis configuration.

This example describes how to configure an expanding Virtual Chassis within a single wiring closet:


This example uses the following hardware and software components:

  • JUNOS 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:

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 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 a Virtual Chassis Interconnected Across Multiple Wiring Closets.

If you want to retain the roles of the existing master and backup switches, explicitly configure the mastership priority of these switches, specifying the highest possible value (255) for both the master 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 the switches using the dedicated VCPs on the rear panel. Do not run the EZ Setup 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 a EX4200-24P switch as a linecard member.

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) or Configuring Gigabit Ethernet Interfaces (J-Web Procedure). For information on configuring uplink ports as Virtual Chassis ports, see Setting an Uplink Module Port as a Virtual Chassis Port (CLI Procedure).

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


master; mastership priority 255


EX4200-24T switch


backup; mastership priority 255


EX4200-24P switch


linecard; mastership 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 Virtual Chassis in Single Wiring Closet

Image g020010-150.gif


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

Note: 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 master 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:

user@SWA-0# set virtual-chassis member 0 mastership-priority 255
user@SWA-1# set virtual-chassis member 1 mastership-priority 255

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

    [edit virtual-chassis]
    user@SWA-0# set member 0 mastership-priority 255
  2. Configure the mastership priority of SWA-1 (member 1) to be the highest possible value. This setting is recommended for high availability and smooth transition of mastership in case the original master becomes unavailable.

    [edit virtual-chassis]
    user@SWA-1# set member 1 mastership-priority 255
  3. Interconnect the unpowered SWA-2 with SWA-0 and SWA-1 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 configure or run EZ Setup on SWA-2. The identification parameters that were set up for the master apply implicitly to all members of the Virtual Chassis configuration. SWA-2 functions in a linecard role, since SWA-0 and SWA-1 have been configured to the highest mastership priority values.


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

Verifying That the New Switch Has Been Added as a Linecard


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


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

user@SWA-0> show virtual-chassis status
Virtual Chassis ID: 0000.e255.00e0

                                       Mastership             Neighbor List  
Member ID  Status  Serial No   Model     Priority  Role       ID Interface

0 (FPC 0)  Prsnt   abc123      ex4200-48p    255  Master*     1 vcp-0
                                                              2 vcp-1

1 (FPC 1)  Prsnt   def456      ex4200-24t    255  Backup      2 vcp-0
                                                              0 vcp-1

2 (FPC 2)  Prsnt   abd231      ex4200-24p    128  Linecard    0 vcp-0
                                                              1 vcp-1


The show virtual-chassis status command lists the member switches of the Virtual Chassis configuration with the member IDs and mastership 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 mastership priority value 128. Because the mastership priority is lower than the mastership 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 mastership 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.

user@SWA-0>show virtual-chassis vc-port all-members

fpc0: -------------------------------------------------------------------------- Interface Type Status or PIC / Port vcp-0 Dedicated Up vcp-1 Dedicated Up fpc1: -------------------------------------------------------------------------- Interface Type Status or PIC / Port vcp-0 Dedicated Up vcp-1 Dedicated Up fpc2: -------------------------------------------------------------------------- Interface Type Status or PIC / Port vcp-0 Dedicated Up vcp-1 Dedicated Up


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 Virtual Chassis ports. There are two dedicated VCPs on the rear panel of each EX4200 switch. It is recommended 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 Mastership Priority


You want to designate a different member as the master.


Change the mastership priority value or values of the switches, designating the highest mastership priority value for the switch that you want to be master.

  1. Lower the mastership priority of the existing master (member 0).

    [edit virtual-chassis]
    user@SWA-0# set member 0 mastership-priority 1
  2. Set the mastership priority of the member that you want to be the master to the highest possible value (255):

    [edit virtual-chassis]
    user@SWA-2# set member 2 mastership-priority 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.

Published: 2009-07-29