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Unified ISSU for Junos OS Evolved

(QFX5220-32CD switches only) Unified in-service software upgrade (ISSU) is a feature that minimizes traffic loss during the software upgrade process.

Understanding Unified ISSU for Junos OS Evolved

The unified in-service software upgrade (unified ISSU) feature enables you to upgrade to a more recent release of Junos OS Evolved with no disruption on the control plane and minimal loss of traffic.

During a unified ISSU, the system restarts the upgraded software (kernel and applications) without reinitializing the underlying hardware. This process is faster than rebooting the complete system. The restarted software restores its previous state and runs the new version.

Unified ISSU provides the following benefits:

  • Eliminates network downtime during software image upgrades.

  • Reduces operating costs while delivering higher service levels.

  • Enables you to implement new features quickly.

Unified ISSU Process on Junos OS Evolved

When you perform a software upgrade using a unified ISSU, the following process occurs:

  1. The system downloads the new software package and performs checks to validate the existing configuration against the new package. This step includes application configuration checks and software development kit (SDK) checks to ensure that you can perform the upgrade by using a unified ISSU.

  2. The software is installed on the system and becomes the next-boot version.

  3. The upgrade software lists the applications that have been changed and that need to be restarted. The upgrade is performed using a restart or a reboot, which the validation process determines.
  4. The system starts to run the new version of software, and the unified ISSU is complete.

Upgrade Scenarios During a Unified ISSU

When you perform a unified ISSU on a Junos OS Evolved device, the validation process determines which of the following methods is required to perform the upgrade:

  • Application restart

  • In-service kernel warm restart

  • System reboot

Application restart involves a simple restart of the upgraded applications. The restarted applications run the new software version. This type of upgrade is hitless and results in zero traffic loss.

In-service kernel warm restart involves loading a new kernel directly into the memory and executing it, without initializing the hardware. This process reduces network downtime and minimizes traffic loss during the upgrade.

System reboot involves a complete reboot of the device, including reinitializing the hardware components. This process is the same as performing an upgrade without using unified ISSU.

The unified ISSU is performed using an in-service kernel warm restart if:

  • The changed components or applications require the device to be restarted.

  • The changed components or applications cannot be upgraded using an application restart.

  • The kernel changed.

You are prompted to confirm the in-service kernel warm restart if changes are made in an application that does not support an application restart. If a major version change is made in the application, then you are prompted to reboot the system to complete the unified ISSU.

In other scenarios, unified ISSU is performed using an application restart.

Validation During a Unified ISSU

Before you perform a unified ISSU, you must validate the new software package against the existing configuration.

The system checks the existing system configuration against the new software package to determine if the two are compatible. It also checks the application configurations and Software Development Kit (SDK) versions to determine whether a hitless upgrade is possible. Note that validation does not actually install the new software package.

The system performs validation by default before you upgrade the device using a unified ISSU. When you add a package with a different release number, the system automatically performs the application configuration validation check and SDK validation check.

If the existing configuration validation fails, the unified ISSU aborts, and an error message provides more information about the failure. If the application configuration validation or the SDK version validation fails, you are prompted to confirm if you want to continue with the ISSU. An error message provides more information about the failure.

If you perform a unified ISSU without successful validations, incompatibilities in the configuration might cause traffic loss during the upgrade.

For more information about how to perform a validation check, see request system software validate-restart .

Note:

Starting in Junos OS Evolved Release 23.4R1, the request system software validate-restart command output summarizes the method required to perform the indicated upgrade, for example, an application restart, an in-service kernel warm restart, or a system reboot.

Unified ISSU Considerations for Junos OS Evolved

Unified ISSU allows you to upgrade to a more recent version of Junos OS Evolved with minimal disruption of traffic and zero downtime.

On Junos OS Evolved, unified ISSU has the following caveats:

  • You cannot use unified ISSU to install a version of Junos OS Evolved that is earlier than the version of Junos OS Evolved currently running on the device.

  • Unified ISSU does not upgrade the firmware as part of the process. You must upgrade the firmware separately.

  • The unified ISSU process is terminated if the current system configuration is not compatible with the new software version.

  • Unified ISSU might cause inaccuracy in the values of filter counters, policer counters, and queue counters.

  • Existing Address Resolution Protocol (ARP) entries will not expire, and new ARP entries will not be added during the ISSU process.

  • During the ISSU process, the system might not respond to ARP requests from peer nodes. To prevent the peer side entries from getting expired during the ISSU window, the peer nodes should be configured to increase the ARP retry count before triggering ISSU.

Perform a Unified ISSU to Upgrade Junos OS Evolved

When you are planning to perform a unified ISSU, choose a time when your network is as stable as possible. As with a normal upgrade, Telnet sessions, SNMP, and CLI access are briefly interrupted.

We recommend that you read the Unified ISSU Considerations for Junos OS Evolved topic to anticipate any special circumstances that might affect your upgrade.

Prerequisites to Performing a Unified ISSU to Upgrade Junos OS Evolved

Before you upgrade your device, follow these steps:

  1. Make sure that you have sufficient disk space for the upgrade and that a backup of the system is available. Save the system configuration and the information about how the system is handling traffic.
    You can do this by following the procedure at Before You Upgrade or Reinstall Junos OS Evolved.
    You will need the information about the system configuration and how the system is handling traffic when you verify that the upgrade was performed correctly.
  2. Download the software package from the Juniper Networks Support website at https://www.juniper.net/support/ and place the package on your local server.
  3. If the BGP protocol is configured on the main routing instance or a specific routing instance, then configure BGP graceful restart and set the restart-time value to greater than or equal to 300 seconds.

    To configure BGP graceful restart and the restart-time value on the main routing instance, execute the following commands:

    To configure BGP graceful restart and the restart-time value on a specific routing instance, execute the following commands:

    Note:

    Changing the restart-time for BGP graceful restart causes the existing BGP sessions to restart, which might cause disruptions. We recommend that you perform this action during a low network usage time to avoid traffic loss.
  4. If a Spanning Tree Protocol (STP) is configured, then configure the STP-enabled ports as edge ports and enable bridge protocol data unit (BPDU) protection.

    Depending on the type of STP configured, execute the following commands:

  5. Configure the value of the Address Resolution Protocol aging-timer to 240 minutes.
  6. Validate the existing configuration against the new software image to check whether it supports unified ISSU by using the request system software validate-restart package-name command.

Upgrade Junos OS Evolved with a Unified ISSU

Make sure that you have completed the steps in Prerequisites to Performing a Unified ISSU to Upgrade Junos OS Evolved before you begin the upgrade.
To upgrade Junos OS Evolved with a unified ISSU:
  1. Run the request system software add package-name restart command on the device that you want to upgrade.
    The system restarts or reboots to load the new software image. When the upgrade is complete, the device displays the login prompt.
  2. At the login prompt, log in and verify the release of the installed software, using the show system software list command.
  3. Verify that the system is running properly and correctly handling traffic by repeating the steps in the procedure in Before You Upgrade or Reinstall Junos OS Evolved. Compare the information about the system configuration to what you collected before you installed the software package.
  4. If you need to make any changes to the configuration after the upgrade, remember to back up the software and configuration using the request system snapshot command. See Back Up and Recover Software with Snapshots.
  5. If the unified ISSU fails for some reason, and if the CLI is still working, you can follow the steps in Recover from a Failed Installation Attempt If the CLI Is Working to install the software image.

Change History Table

Feature support is determined by the platform and release you are using. Use Feature Explorer to determine if a feature is supported on your platform.

Release
Description
23.4R1-EVO
Starting in Junos OS Evolved Release 23.4R1, the request system software validate-restart command output summarizes the method required to perform the indicated upgrade, for example, an application restart, an in-service kernel warm restart, or a system reboot.