The Cisco IOS Command Interpreter
Now that we have installed (or upgraded) the router's IOS, it is time to look inside and see what makes the IOS work. The core component of the Cisco IOS is the Cisco command interpreter, also known as the Exec. This section will introduce you to the command interpreter and its different modes.
As was mentioned in the "Introduction" at the beginning of today's lesson, the Cisco IOS provides two levels of access to the IOS command structure. These levels are known as Exec modes or command interpreter modes. If you look back at the procedures for upgrading the IOS in the preceding section, you will notice that there are two different prompts at which commands can be entered within the Cisco IOS. These prompts represent the mode under which the user is accessing the command interpreter.
The first (most basic) mode is known as user mode. User mode is signified by a > sign as a command prompt.
From user mode the router engineer can execute the more basic commands, such as those used to view router properties or make temporary changes to the terminal settings. No password access is required to access the user mode of the Exec.
The following are some of the more common user mode commands:
Although these commands are not capable of setting global configurations or permanently changing the router's functionality, they offer enough power to gather information and track a router's general health.
The second (more advanced) level of the Exec is privilege mode. The privilege mode command prompt is indicated by a # character.
To access the privilege mode of the command interpreter, use the enable command from the user mode command prompt.
Router>enable Password: Router#
For security reasons, access to the privilege mode command interpreter can be blocked by a password. (We will discuss setting these passwords in Day 6, "Getting the Router Up and Running.")
Within privilege mode, the router engineer can access all of the functionality of the router. Tools for configuring the router's interfaces, connecting to external sources, loading protocols, and moving and deleting files are all available through the privilege mode of the command interpreter.
Some commonly used privilege level commands are
The next lesson, "Learning the Cisco User Interface," will dive deeper into the commands and tools that can be accessed from the two modes of the command interpreter. While you are learning the Cisco user interface, you will use and become acquainted with the various commands used to maintain the router. Before going on to the next lesson, try some of these questions based on today's lesson.