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The Cisco IOS—Basic Router Commands

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The Cisco IOS—Basic Router Commands

Cisco has divided its CCNA exam objectives into nine categories. Category 9, "Cisco Basics, IOS & Network Basics," lists IOS CLI Router as an objective. This is one of the most important objectives for the exam and requires that you know how to execute a wide range of commands from the router's command-line interface. This objective is covered in this chapter and continues in Chapters 4, "The Cisco IOS—Configuration Commands and Passwords," and 5, "The Cisco IOS—Configuration Files and IOS Images." This chapter also covers one objective, Telnet, from the Network Management Category.

  • IOS CLI Router

  • Telnet

Objective 10 : IOS CLI Router—Basic Commands

The Cisco Internetworking Operating System (IOS) is the software that provides the router hardware with the capability to route packets on an internetwork. The IOS (just like any other operating system) provides the command sets and software functionality you use to monitor and configure the router, and it also provides the functionality for the various protocols—both routed and routing—that make internetworking a reality.

Cisco provides a command-line interface (CLI) you can use to interact with the router's IOS and maintain and configure your router. You can access the CLI using a router console or by telnetting to a router using a virtual terminal. When you log in to a router, you are placed in the user EXEC mode (one mode of the EXEC command interpreter), meaning that commands typed at the prompt are executed and a response is provided by the IOS on the console or virtual terminal screen.

The user mode enables you to examine the router's settings and telnet out to other routers on the internetwork (if you have the virtual terminal password for the router to which you want to telnet). The user mode enables you to perform only a limited examination of the router and its configuration.

The EXEC command interpreter also has a second mode—the privileged mode. The privileged mode provides a larger set of commands than the user mode, enabling you to view your currently running configuration and the startup configuration for the router. It also enables you to copy configuration files and IOS images (actual IOS files) to and from the router using a Trivial File Transfer Protocol (TFTP) server (more about TFTP in Chapter 5). More importantly, the privileged mode enables you to enter the configuration mode and change the router's configuration (more about router configuration in Chapter 4 when we discuss using the setup command).

You can log in to a router using a console connection, auxiliary connection (enabling you to dial in to the router using a modem), or virtual terminal connection via telnet (by logging in to the router from another host on the network, such as another router; Telnet is discussed later in the chapter). Login is required for only a particular connection (such as from the console or virtual terminal if a login password has been set).

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