DAL Firmware Downgrade: Configuration Fails To Load Due To Schema Discrepancy

Introduction

Important: A firmware downgrade will cause a factory reset of the device. This knowledge base article provides a workaround intended to help preserve configuration usability and avoid configuration load issues that can occur after a downgrade.

When downgrading DAL firmware to a previous version, the device configuration may fail to load due to a schema discrepancy between firmware versions. This article describes the cause of this issue and provides a workaround to prevent configuration load failure by removing the schema section from the configuration file before downgrading.

Prerequisites

• Administrative access to the DAL device
• SSH or serial console access to the device
• Familiarity with basic Linux command-line editing (e.g. vi, nano)
• A backup of your current configuration file (strongly recommended)

Solution

DAL firmware versions use configuration schemas that may differ between releases. When firmware is downgraded, the device attempts to load a configuration file saved under a newer schema version. The older firmware cannot parse the newer schema structure, causing the configuration to fail to load. To prevent this, connect to the device before downgrading and manually remove the schema section from the configuration file /etc/config/accns.json. This prevents the configuration load failure in most cases.

Warning: A firmware downgrade causes a factory reset. Although this workaround is effective in most situations, there is still a risk that a device may downgrade successfully while configuration recovery does not behave as expected. Always perform a full backup of the device configuration and assess operational risk before proceeding.

Removing the Schema Section Before Firmware Downgrade

• Connect to the device via SSH or serial console — Establish a terminal session with administrative privileges before making any changes.
• Back up the configuration file — Run the following command to create a backup before editing: cp /etc/config/accns.json /etc/config/accns.json.old
• Open the configuration file in a text editor — For example, using vi: vi /etc/config/accns.json
• Locate and fully remove the schema section — Find the JSON block that defines the schema (typically a top-level key such as schema or @schema) and delete it entirely, including its opening key, braces, and any trailing comma, ensuring the remaining JSON is still valid.

            "schema": {
                     "version": "XXXX"
            },

• Save the file and exit the editor — Verify the file is saved successfully before proceeding.
• Proceed with the firmware downgrade — Initiate the downgrade using your standard procedure. The device should now load the configuration without a schema-related failure.
• Verify the configuration loaded successfully — After reboot, confirm all settings (network interfaces, VPNs, services) are active and functioning as expected.

Important Notes

• This workaround is intended to work in most scenarios but is not guaranteed in every environment or configuration state.
• A firmware downgrade causes a factory reset; ensure appropriate backups are taken beforehand.
• There remains a risk that the downgrade process or subsequent configuration restoration may not produce the expected outcome.
• This procedure is not officially recommended for critical infrastructure environments — assess the risk before applying it in production.
• Always back up the configuration file before editing it.
• Ensure the edited JSON remains syntactically valid after removing the schema section; invalid JSON will prevent the configuration from loading.
• SSH or serial console access must be established before the downgrade begins — access may be unavailable if the configuration fails to load post-downgrade.