Discussion

the CLI (on the router) or by using any ASCII text editor (on a server). From J-Web,
the configuration is saved in an ASCII file that you can read using J-Web, the CLI, or
an ASCII text editor.
JUNOS CLI Modes
Throughout this book, we’ll show you how to use the JUNOS CLI to configure and
monitor the router. While it is beyond the scope of this book to describe the design
of the CLI and all its capabilities, this section gives an overview of the CLI modes
and describes a few of the basic features. Throughout the rest of this chapter, we’ll
give more examples of CLI features. For complete information about the JUNOS
CLI, refer to the JUNOS product documentation on the Juniper Networks web site,
http://www.juniper.net/techpubs.
The underlying operating system for the JUNOS software is FreeBSD. As we talk
about the various CLI commands, if a command is derived from FreeBSD or a standard
Unix utility, or is simply the FreeBSD or Unix command packaged with a
JUNOS name, we will mention the command it is based on. If you are already familiar
with the FreeBSD or Unix equivalent, this will help you understand the JUNOS
command.
The CLI has two modes: operational mode and configuration mode. Both modes
have distinct commands. In operational mode, you monitor everything about the
router’s hardware and software and check on network operation. In configuration
mode, the commands let you define the behavior of the router, such as indicating
what network addresses to use and protocols to run. It is important for you to understand
the differences between these two modes, what types of actions you can take in
which mode, and how to keep track of which mode you are working in. Throughout
the rest of this book, we’ll show you how to work in both modes as you configure
the router and verify its operation.
On the router, you can identify which mode you are in by looking at the CLI
prompt. The base prompt has the format username@router-name. When you are in
operational mode, the prompt ends with a >; when you are in configuration mode,
the prompt ends with a #. We follow this same convention throughout this book, so
by paying attention to the prompt that precedes each command, you can determine
whether you issue the command in operational or configuration mode.
When you first log in to a JUNOS router, you are in operational mode. The commands
available in operational mode let you monitor router and network operations.
For example, you can get information about the router’s hardware and
software, the network traffic that is coming to the router, and configured routing
protocols. Throughout this book, we’ll show you how to use operational mode commands
to check what is happening on the router.
2 | Chapter 1: Router Configuration and File Management
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