You use configuration files to configure devices and to streamline device configuration tasks. A configuration file stores the complete configuration of a device. Keep in mind these distinctions between configuration files:

• The active (running) configuration is the operational file of the device. These files control device behavior.

• The candidate configuration is the working copy that stores configuration updates. These are the files that you use to automatic device configuration.

A configuration file stores the complete configuration of a network device. The current configuration of a device is called the active configuration. You can alter this current configuration, and you can also return to a previous configuration or to a rescue configuration.

The 50 most recently committed configuration files on a device are saved so that you can return to a previous configuration. The configuration files are named as follows:

• juniper.conf.gz  – The current active configuration

• juniper.conf.1.gz to juniper.conf.49.gz. – Rollback configurations

To make changes to the configuration file, you must use configuration mode in the CLI. When making changes to a configuration file, you are viewing and changing the candidate configuration file. The candidate configuration enables you to make configuration changes without causing operational changes to the active configuration or causing potential damage to your current network operations. After you commit the changes you made to the candidate configuration, the system updates the active configuration.

Configuration File Terms

• active configuration – Current committed configuration of a device.
• candidate configuration – Working copy of the configuration that enables users to make configurational changes without causing any operational changes until this copy is committed.
• configuration group – Group of configuration statements that the rest of the configuration can inherit.
• commit a configuration – The act of checking a configuration for proper syntax, activating it, and marking as the current configuration file running on the device.
• configuration hierarchy – A hierarchy of statements comprising the system configuration. The two types of statements are container and leaf: Container statements contain other statements. Leaf statements do not contain other statements. All the container and leaf statements together form the configuration hierarchy.
• default configuration – The initial values set for each configuration parameter when a device is shipped.
• rescue configuration – Well-known configuration that recovers a device from a configuration that denies management access. Through the CLI, you set a current committed configuration to be the rescue configuration.
• roll back a configuration – The act of returning to a previously committed configuration.