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Example: Changing the Configuration Using Python Op Scripts

 

Op scripts enable you to make controlled changes to the Junos OS configuration. Op scripts are advantageous, because they can gather operational information about a device and update the configuration based on that information. Experienced users who are familiar with Junos OS can write op scripts that prompt for the relevant configuration information and modify the configuration accordingly. This enables users who have less experience with Junos OS to safely modify the configuration using the script. This example demonstrates how to make changes to the Junos OS configuration using a Python op script that leverages Junos PyEZ APIs.

Requirements

This example uses the following hardware and software components:

  • MX Series router running Junos OS Release 16.1R3 or later release that includes the Python extensions package.

Overview and Op Script

Python op scripts can make changes to the Junos OS configuration using the Junos PyEZ jnpr.junos.utils.config.Config utility. The Junos PyEZ Config utility provides instance methods to lock the configuration, load the configuration data and specify how to integrate it into the configuration, commit the configuration, and unlock the configuration. For more information about using Junos PyEZ to configure devices running Junos OS, see Using Junos PyEZ to Configure Devices Running Junos OS. The Python op script in this example demonstrates how to update the configuration to disable an interface on the local device.

The Python op script imports the following:

  • Device class—handles the connection with the device running Junos OS

  • Config class—performs configuration mode commands on the target device

  • jnpr.junos.exception module—contains exceptions encountered when managing devices running Junos OS

  • jcs module—enables the script to execute supported extension functions

In this example, the usage variable is initialized with a general description of the script’s function. When the script is executed, the script outputs the usage description on the CLI so that the user can verify the purpose for that script.

The script calls the jcs.get_input() extension function, which prompts the user to enter the name of the interface to disable, and stores the interface name in the interface variable. The config_xml variable is an XML string that defines the configuration changes.

The script does not supply a host parameter when creating the Device instance, which causes the open() method to establish a connection with the local device. This example creates the Config instance by using a context manager with mode='exclusive' to obtain an exclusive lock on the configuration while it’s being modified. In this mode, the context manager automatically handles locking and unlocking the candidate configuration. The Config utility methods load the configuration changes into the candidate configuration as a load merge operation and commit the configuration. The dev.close() method closes the connection.

Python Script

Device Configuration

To download, enable, and test the script:

  1. Copy the script into a text file, name the file config-change.py, and copy it to the /var/db/scripts/op/ directory on the device.Note

    Unsigned Python scripts must be owned by either root or a user in the Junos OS super-user login class, and only the file owner can have write permission for the file.

  2. In configuration mode, include the file config-change.py statement at the [edit system scripts op] hierarchy level.

  3. Enable the execution of unsigned Python scripts on the device.

    Note

    The language python statement executes scripts using Python 2.7. To use Python 3 to execute Python scripts on devices running Junos OS Release 19.4R1 or later, configure the language python3 statement instead.

  4. Issue the commit and-quit command to commit the configuration and to return to operational mode.

  5. Before running the script, issue the show interfaces interface-name operational mode command and record the current state of the interface that will be disabled by the script.
  6. Execute the op script by issuing the op config-change.py operational mode command.
    user@host> op config-change.py

Verification

Verifying the Commit

Purpose

Verify that the commit succeeded.

Action

You should include code in your script that catches any warnings or errors associated with changing and committing the configuration. This enables you to more easily determine whether the commit succeeded. If there are no warning or error messages, you can verify the success of the commit in several ways.

  • Check the commit log to verify that the commit was successful.

    user@host> show system commit
  • Check the syslog message file to verify that the commit operation was logged. In this case, you also see an SNMP_TRAP_LINK_DOWN message for the disabled interface. Depending on your configuration settings for traceoptions, this message might or might not appear in your log file.

    user@host> show log messages | last

Verifying the Configuration Changes

Purpose

Verify that the correct changes are integrated into the configuration.

Action

  • Display the configuration and verify that the changes are visible for the specified interface.

    user@host> show configuration interfaces so-0/0/0
  • For this example, you also can issue the show interfaces interface-name operational mode command to check that the interface was disabled. In this case, the output captured before the interface was disabled shows that the interface is Enabled.

    user@host> show interfaces so-0/0/0

    The output captured after running the script to disable the interface shows that the interface is now Administratively down.

    user@host> show interfaces so-0/0/0