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Upgrading Software on a Virtual Chassis Fabric Using Nonstop Software Upgrade

Nonstop software upgrade (NSSU) enables you to upgrade the software running on all member switches in a Virtual Chassis Fabric (VCF) with minimal network traffic disruption during the upgrade.

For an overview of the benefits of NSSU and how NSSU works, see Understanding Nonstop Software Upgrade on a Virtual Chassis Fabric.

Preparing the Switch for the New Software Installation

Before you begin software installation using NSSU:

  • Ensure that the VCF is configured correctly to support NSSU:

    • Verify that you connected the VCF members in a spine-and-leaf topology with each leaf device connected to all of the configured spine devices. A spine-and-leaf topology prevents the Virtual Chassis from splitting during an NSSU.


      NSSU is supported in a QFX5100 VCF with up to 20 members.

      NSSU is not supported in a QFX5110 VCF.

    • Ensure the VCF is preprovisioned and you explicitly assigned the Routing Engine role or linecard role to the member switches acting in each of those roles.

    • Make sure the preprovisioned configuration has only two members in the Routing Engine role. The NSSU process checks the member configuration, displays a warning message if it detects that you configured more than two switches in the Routing Engine role, and stops the upgrade.

    • In a two-member Virtual Chassis, configure no-split-detection so that the VCF does not split when an NSSU upgrades a member.

    • You can optionally configure NSSU upgrade groups with multiple linecard role members in each upgrade group.NSSU upgrades the members in each upgrade group simultaneously, which can shorten the NSSU process, and upgrades the upgrade groups in the order in which you configured them.

      See Configuring Line-Card Upgrade Groups for Nonstop Software Upgrade for details.

  • Check that members are running the same version of the software:

    If the Virtual Chassis Fabric members are not running the same version of the software, use the request system software add CLI command to upgrade the software on the inconsistent members. If some member switches do not run the same software image, specify different package names using the set option: request system software add set [package-namepackage-name ...] reboot.

    For example:

  • Verify that you enabled nonstop active routing (NSR) and graceful Routing Engine switchover (GRES).You only need to check the NSR state—if NSR is enabled, then GRES is also enabled:

    If nonstop active routing is not enabled (Stateful Replication is Disabled), see Example: Configuring Nonstop Active Routing on Switches for information on how to enable it.

  • Verify that you enabled nonstop bridging (NSB), which ensures that all NSB-supported Layer 2 protocols operate seamlessly during the Routing Engine switchover that happens during NSSU.

  • (Optional) Back up the system software—Junos OS, the active configuration, and log files—on each member to an external storage device with the request system snapshot command.

Upgrading the Software Using NSSU

This procedure describes how to upgrade the software running on all VCF members using NSSU. When the upgrade completes, all members are running the new version of the software. Because a graceful Routing Engine switchover occurs during the upgrade, the original VCF backup is the new primary at the end of the NSSU process.

During NSSU, the primary copies the new software image to all the members in the VCF and reboots them in turn. If copying the new software to a member fails or rebooting a member fails, NSSU terminates the upgrade process and logs the error. In this case, you must manually perform recovery measures for members left in an incompatible state, to restore all members to running the same version of the software. Starting in Junos OS Release 14.1X53-D40, NSSU automatically invokes recovery measures after either of these failures, as follows:

  • if NSSU terminates due to a copy error, the new image is removed from any members to which it was already copied.

  • If any member fails to reboot, NSSU automatically initiates a clean VCF restart by bringing down and rebooting the entire VCF. All members come up running the new software at the same time. This action cleanly recovers stable VCF operation more quickly than having an unstable VCF running different versions of the software trying to converge.


Junos OS software images with enhanced automation are only supported on a non-mixed VCF with QFX5100 switches. Also, performing an NSSU from a standard Junos OS software image to a Junos OS software image with enhanced automation, or from a Junos OS software image with enhanced automation to a standard Junos OS software image is not supported.

To upgrade all members of the VCF using NSSU:

  1. Download the software package. If you are upgrading the software running on a mixed mode VCF, download the software packages for each switch type.

  2. Copy the software package or packages to the VCF primary switch. We recommend that you copy the file to the /var/tmp directory on the primary.

  3. Log in to the VCF using the console connection of the primary or the virtual management Ethernet (VME) interface. Without the console connection, you will not be able to view any CLI output during an NSSU reboot. The console connection enables you to view CLI output during an NSSU reboot and monitor the progress of the primary switch reboot.

  4. Start the NSSU operation:

    • To perform NSSU on a VCF composed all of one type of switch, enter:

      where package-name.tgz is, for example, jinstall-qfx5100.tgz.

    • To perform NSSU on a mixed-mode QFX5100 VCF (QFX5100 switches with some combination of QFX3500,QFX3600, or EX4300 switches), enter:

      where [package-name.tgz package-name.tgz package-name.tgz] is, for example, [jinstall-qfx5100.tgz jinstall-qfx3500.tgz jinsall-ex-4300.tgz].

    As the upgrade proceeds, the VCF displays status messages similar to the following sample output for an NSSU operation on a QFX5100 VCF with four QFX5100 member switches:

  5. Log in after the reboot of the original primary switch completes. To verify that the software on all Routing Engines in the VCF members has been upgraded, enter the following command: