Summary

The os-forward-compat-12 package is a temporary compatibility mechanism that:

• Enables config validation during BSD12 → BSD15 upgrades
• Provides limited system call compatibility needed for validation components
• Is automatically used when available and removed when no longer needed

Failure to use it (when required) results in:

• Validation failures
• Need to bypass validation during upgrade

Detailed Description

The os-forward-compat-12 package is a compatibility package used during upgrades from BSD12-based Junos releases to BSD15-based Junos releases.

Its purpose is to enable configuration validation during the upgrade process by providing additional system call support required for components of the target (BSD15-based) release to execute while the system is still running on a BSD12 kernel.

This allows the system to perform validation of the existing configuration against the target release before the upgrade proceeds.

Key characteristics:

• The package is typically bundled with BSD15-based Junos images and is not always present in older releases.
• When available, it is automatically added and activated if configuration validation is attempted during upgrade.
• It is only used temporarily during the validation phase and is not intended for normal runtime use.
• The package deactivates itself when no longer required after validation or upgrade completion.

In cases where it is not included in the Junos image, it can be manually installed if provided.

The absence of the os-forward-compat-12 package (or inability to use it during upgrade) may result in the following symptoms:

• Configuration validation failure during upgrade from BSD12 to BSD15-based releases
• Error messages indicating missing support required by the target system (for example, kernel or capability mismatches)
• Requirement to use upgrade commands with no-validate to proceed (bypassing validation)

Additional operational observations:

• The package may not be available in all builds or platforms unless explicitly bundled.
• It has been noted that:
  • Certain platforms (e.g., EX4100) may encounter issues (e.g., related to mmap calls from management processes), requiring further investigation. 
• The feature may have limited test coverage in some environments because internal testing often uses validation bypass methods.

Recommended Approach (When Package is Bundled)

If the os-forward-compat-12 package is included in the Junos image:

• No manual action is required
• The system will:
  • Automatically add the package
  • Load the required module
  • Perform configuration validation successfully

This is the expected and preferred behavior for supported upgrade paths.

Manual Installation (If Package is Missing)

If the package is not bundled and validation is required:

1. Obtain the package from JTAC
   • The package is not available for direct customer download 1
2. Install manually using:

request system software add /var/tmp/os-forward-compat-12.tgz

After installation:

• The package will be used automatically during validation if needed

Workaround (If Package is Unavailable)

If the package cannot be obtained or used:

• Proceed with upgrade using:
  • no-validate option

Note:

• This bypasses configuration compatibility checks
• Should be used with caution and only when validation cannot be completed

Lifecycle Behavior

• The package:
  • Activates only when validation is attempted
  • Is not required after upgrade completes
  • Deactivates automatically when no longer needed

2026-06-26 Published

First draft 2026-05-27