Understanding CLI Command Modes

The CLI has two modes:

• Operational mode—This mode displays the current router status. In operational mode, you enter commands to monitor and troubleshoot the software, network connectivity, and router.
• Configuration mode—A router configuration is stored as a hierarchy of statements. In configuration mode, you enter these statements to define all properties of the JUNOS software, including interfaces, general routing information, routing protocols, user access, and several system hardware properties.

When you enter configuration mode, you are actually viewing and changing a file called the candidate configuration. The candidate configuration allows you to make configuration changes without causing operational changes to the current operating configuration, called the active configuration. The router does not implement the changes you added to the candidate configuration until you commit them, which activates the configuration on the router. (See Figure 2.) Candidate configurations enable you to alter your configuration without causing potential damage to your current network operations.