The CLI has two modes, operational and configuration. In operational mode, you monitor and troubleshoot the software, network connectivity, and the router by entering CLI commands. For more information on operational mode, see Command-Line Interface Operational Mode.
When in configuration mode, you configure the JUNOS software by creating a hierarchy of configuration statements. You can do this by using the CLI or by creating a text (ASCII) file that contains the statement hierarchy. (The statement hierarchy is identical in both the CLI and text configuration file.) You can configure all properties of the JUNOS software, including interfaces, general routing information, routing protocols, and user access, as well as several system hardware properties. When you have finished entering the configuration statements, you commit them, which activates the configuration on the router. For more information about configuration mode, see Configure the Router with the CLI.