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The IOS User Interface

181

And just as it was with preceding chapters, the fundamentals that you’ll learn in this chapter

are foundational building blocks that really need to be in place before you go on to the next

chapters in the book.

For up-to-the-minute updates for this chapter, please see

www.lammle.com

and/or

www.sybex.com/go/ccent

The IOS User Interface

The

Cisco Internetwork Operating System (IOS)

is the kernel of Cisco routers and most switches.

In case you didn’t know, a kernel is the basic, indispensable part of an operating system that allo-

cates resources and manages things such as low-level hardware interfaces and security.

In the following sections, I’ll show you the Cisco IOS and how to configure a Cisco router

using the command-line interface (CLI). We’ll use Cisco’s SDM toward the end of the chapter.

I’m going to save Cisco switch configurations for Chapter 7, “Layer 2

Switching.”

Cisco Router IOS

The Cisco IOS is a proprietary kernel that provides routing, switching, internetworking,

and telecommunications features. The first IOS was written by William Yeager in 1986,

and it enabled networked applications. It runs on most Cisco routers as well as an ever-

increasing number of Cisco Catalyst switches, like the Catalyst 2950/2960 and 3550/3560

series switches.

These are some important things that the Cisco router IOS software is responsible for:

Carrying network protocols and functions

Connecting high-speed traffic between devices

Adding security to control access and stop unauthorized network use

Providing scalability for ease of network growth and redundancy

Supplying network reliability for connecting to network resources

You can access the Cisco IOS through the console port of a router, from a modem into the

auxiliary (or Aux) port, or even through Telnet. Access to the IOS command line is called an

EXEC session

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