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Accessing the Cisco IOS CLI

Like any other piece of computer hardware, Cisco switches need some kind of operating
system software. Cisco calls this OS the Internetwork Operating System (IOS).

Cisco IOS Software for Catalyst switches implements and controls logic and functions performed
by a Cisco switch. Besides controlling the switch’s performance and behavior, Cisco
IOS also defines an interface for humans called the CLI. The Cisco IOS CLI allows the user
to use a terminal emulation program, which accepts text entered by the user. When the user
presses Enter, the terminal emulator sends that text to the switch. The switch processes the
text as if it is a command, does what the command says, and sends text back to the terminal
emulator.

The switch CLI can be accessed through three popular methods—the console, Telnet, and
Secure Shell (SSH). Two of these methods (Telnet and SSH) use the IP network in which the
switch resides to reach the switch. The console is a physical port built specifically to allow
access to the CLI. Figure 6-2 depicts the options.
Free CISCO CCNA Routing and Switching ICND1 Study Guide
Figure 6-2 CLI Access Options

Console access requires both a physical connection between a PC (or other user device)
and the switch’s console port, as well as some software on the PC. Telnet and SSH require
software on the user’s device, but they rely on the existing TCP/IP network to transmit data.
The next few pages detail how to connect the console and set up the software for each
method to access the CLI .

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