To configure the JUNOS software, you specify a hierarchy of configuration statements that define the desired software properties. You can configure all properties of the JUNOS software, including interfaces, general routing information, routing protocols, and user access, as well as some system hardware properties. After you have created a candidate configuration, you commit the configuration to be evaluated and activated by the JUNOS software.
There are two basic ways to configure the JUNOS software:
When you initially boot a router, the system prompts you for the minimal information needed to configure the router, including the router's name, domain name, and the Internet address of at least one interface on the router. After the router finishes this initial boot, you login as the user "root" (with no password) and configure a password for the user "root."
After completing this initial minimal configuration, you can configure all the desired software properties. If you configure the software interactively using the CLI, you enter software configuration statements to create a candidate configuration that contains a hierarchy of statements. At any given hierarchy level, you generally can enter statements in any order. While you are interactively configuring the software, you can display all or portions of the candidate configuration, and you can insert or delete statements. Any changes you make affect only the candidate configuration, not the active configuration that is running on the router.
The configuration hierarchy logically groups related functions together, which results in configuration statements that have a regular, consistent syntax. As examples, you configure routing protocols, routing policies, interfaces, and SNMP management each in their own separate portion of the configuration hierarchy.
At each level of the hierarchy, you can display a list of the statements available at that level, along with short descriptions of the statements' functions. To have the CLI complete the statement name if it is unambiguous or to provide a list of possible completions, you can type a partial statement name followed by a space or tab.
More than one user can edit a router's configuration simultaneously. All changes made by all users are visible to everyone editing the configuration.
To have a candidate configuration take effect, you commit the changes. At this point, the candidate file is checked for proper syntax, activated, and marked as the current, operational software configuration file. If multiple users are editing the configuration, when you commit the candidate configuration, all changes made by all the users take effect.
The CLI always maintains a copy of previously committed versions of the software configuration. If you need to return to a previous configuration, you can do this from within the CLI.