Configuration validation for image upgrade or downgrade

When you install a new version of Junos OS on the switch, the system validates that the existing configuration is compatible with the new image. Without the validation feature, configuration incompatibilities or insufficient memory to load the new image might cause the system to lose its current configuration or go offline. With the validation feature, if validation fails, the new image is not loaded, and an error message provides information about the failure. 

Image validation is supported only on the jinstall package. 

If you invoke validation from an image that does not support validation, the new image is loaded but validation does not occur. 

Invoke validation by issuing either request system software add or request system software nonstop-upgrade. You can also issue request system software validate to run just configuration validation. 

Image validation does not work in a downgrade from Release 17.4 to 17.2 or earlier if graceful switchover is enabled and image loading is done without NSSU. Use one of the following options: 

• To downgrade with graceful switchover but without image validation-Issue the request system software add image-name reboot no-validate command. 
• To downgrade with image validation but without graceful switchover-Remove the graceful-switchover configuration and then issue the request system software add image-name reboot command. 
• To downgrade with image validation and graceful switchover-Use NSSU by issuing the request system software nonstop-upgrade image-name command.