You can configure all properties of Junos OS, including interfaces, general routing information, routing protocols, and user access, as well as several system hardware properties.

As described in Understanding the Junos OS CLI Modes, Commands, and Statement Hierarchies, a router configuration is stored as a hierarchy of statements. In configuration mode, you create the specific hierarchy of configuration statements that you want to use. When you have finished entering the configuration statements, you commit them, which activates the configuration on the router.

You can create the hierarchy interactively or you can create an ASCII text file that is loaded onto the router or switch and then committed.

This topic covers:

• Configuration Mode Commands
• Configuration Statements and Identifiers
• Configuration Statement Hierarchy

Figure 1: Configuration Mode Hierarchy of Statements

Each statement at the top level of the configuration hierarchy resides at the trunk (or root level) of a hierarchy tree. The top-level statements are container statements, containing other statements that form the tree branches. The leaf statements are the leaves of the hierarchy tree. An individual hierarchy of statements, which starts at the trunk of the hierarchy tree, is called a statement path. Figure 1 illustrates the hierarchy tree, showing a statement path for the portion of the protocol configuration hierarchy that configures the hello interval on an interface in an OSPF area.

The protocols statement is a top-level statement at the trunk of the configuration tree. The ospf, area, and interface statements are all subordinate container statements of a higher statement (they are branches of the hierarchy tree); and the hello-interval statement is a leaf on the tree which in this case contains a data value: the length of the hello interval, in seconds.

The CLI represents the statement path shown in Figure 1
as [edit protocols ospf area area-number interface interface-name] and displays the configuration as follows:

The CLI indents each level in the hierarchy to indicate each statement’s relative position in the hierarchy and generally sets off each level with braces, using an open brace at the beginning of each hierarchy level and a closing brace at the end. If the statement at a hierarchy level is empty, the braces are not printed.

Each leaf statement ends with a semicolon. If the hierarchy does not extend as far as a leaf statement, the last statement in the hierarchy ends with a semicolon.

The configuration hierarchy can also contain “oneliners” at the last level in the hierarchy. Oneliners remove one level of braces in the syntax and display the container statement, its identifiers, the child or leaf statement and its attributes all on one line. For example, in the following sample configuration hierarchy, the line level 1 metric 10 is a oneliner because the level container statement with identifier 1, its child statement metric, and its corresponding attribute 10 all appear on a single line in the hierarchy:

Likewise, in the following example, dynamic-profile dynamic-profile-name aggregate-clients; is a oneliner because the dynamic-profile statement, its identifier dynamic-profile-name, and leaf statement aggregate-clients all appear on one line when you run the show command in the configuration mode: