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Juniper JUNOS Fundamentals

2.4 JUNOS Reverting to previous configurations

In Junos, you can revert to a previous configuration by using the "rollback" command. The rollback command allows you to return to a previous version of the configuration that has been previously saved in the Junos configuration file.

The rollback command takes the following format:

rollback <number> 
Where <number> is the number of the previous configuration that you want to
revert to.

For example, if you want to revert to the previous configuration, you would use the following command: rollback 1

Once you have issued the rollback command, the device will compare the current active configuration with the specified previous configuration, and it will automatically merge any changes that were made in the meantime.

It's important to note that when you revert to a previous configuration, you will lose any changes that have been made to the active configuration since the previous configuration was saved. This makes it important to save a copy of the current configuration before reverting to a previous configuration, in case you need to revert back to the current configuration later.

Additionally, before committing a change, you can preview the changes you made to the candidate configuration by using the "show | compare" command, which will show you the difference between the current active configuration and the candidate configuration.

3. JUNOS Modifying, managing, and saving configuration files

In Junos, you can modify, manage, and save configuration files by using the following CLI commands:

  • 1. Modifying the configuration: You can modify the configuration by using the "set" command. The set command is used to add, modify, or delete configuration statements. For example, to modify the hostname of the device, you would use the following command:

    set system host-name <new-hostname>

  • 2. Managing the configuration: You can manage the configuration by using the "commit" and "rollback" commands. The "commit" command is used to apply changes to the active configuration, while the "rollback" command is used to revert to a previous configuration. Before committing a change, it's a best practice to check the changes you made to the configuration using the "show | compare" command.

  • 3. Saving the configuration: You can save the configuration by using the "commit and-quit" command or the "copy running-configuration startup-configuration" command. The "commit and-quit" command will save the current configuration and then exit the CLI, while the "copy running-configuration startup-configuration" command will save the current configuration to the startup configuration file, which will be used the next time the device is restarted.

It's important to note that when you save the configuration, you are saving the changes to the startup configuration file, which will be used the next time the device is restarted. If you make changes to the configuration and do not save them, they will be lost if the device is restarted or if you exit the CLI.

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