most of its Catalyst LAN switch products. The CLI is a text-based interface in which the
user, typically a network engineer, enters a text command and presses Enter.
The switch does what the command says, and in some cases, the switch replies with some messages stating the results of the command.
Cisco refers to a switch’s physical connectors as either interfaces or ports. Each interface
has a number in the style x/y, where x and y are two different numbers.
Cisco supports two major types of switch operating systems: Internetwork Operating
System (IOS) and Catalyst Operating System (Cat OS). Most Cisco Catalyst switch series today run only Cisco IOS, but for some historical reasons, some of the high-end Cisco LAN
switches support both Cisco IOS and Cat OS.
Switch Status from LEDs
When an engineer needs to examine how a switch is working to verify its current status
and to troubleshoot any problems, the vast majority of the time is spent using commands
from the Cisco IOS CLI.
However, the switch hardware does include several LEDs that provide some status and troubleshooting information.
For example, SYST LED
■ Off: The switch is not powered on
■ On (green): The switch is powered on and operational (Cisco IOS has been loaded)
■ On (amber): The switch’s Power-On Self Test (POST) process failed, and the Cisco
IOS did not load.
STAT (status) mode
■ Off: The link is not working.
■ Solid green: The link is working, but there’s no current traffic.
■ Flashing green: The link is working, and traffic is currently passing over the interface.
■ Flashing amber: The interface is administratively disabled or has been dynamically
disabled for a variety of reasons.
Accessing the Cisco IOS CLI
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.
SSH encrypts all data exchange, including login passwords; Telnet encrypts
nothing.
CLI Access from the Console
Every Cisco switch has a console port, which is physically an RJ-45 port. A PC connects to the console port using a UTP rollover cable, which is also connected to the PC’s serial port.
UTP rollover cable has RJ-45 connectors on each end, with pin 1 on one end connected to pin 8 on the other, pin 2 to pin 7, pin 3 to pin 6, and pin 4 to pin 5.
The default console port settings on a switch are as follows:
■ 9600 bits/second
■ No hardware flow control
■ 8-bit ASCII
■ No stop bits
■ 1 parity bit
User and Enable (Privileged) Modes
User EXEC mode, sometimes also called user mode, allows the user to look around but not break anything.
A more powerful EXEC mode called enable mode (also known as privileged mode or privileged EXEC mode). Enable mode is so named because the enable command is used to reach this mode.
Storing Switch Configuration Files
Cisco switches contain Random Access Memory (RAM) to store data while Cisco IOS is using it, but RAM loses its contents when the switch loses power.
The following list details the four main types of memory found in Cisco switches:
■ RAM: Sometimes called DRAM for Dynamic Random-Access Memory, RAM is
used by the switch just as it is used by any other computer: for working storage. The
running (active) configuration file is stored here.
■ ROM: Read-Only Memory (ROM) stores a bootstrap (or boothelper) program that is
loaded when the switch first powers on. This bootstrap program then finds the full
Cisco IOS image and manages the process of loading Cisco IOS into RAM.
■ Flash memory: Either a chip inside the switch or a removable memory card, Flash
memory stores fully functional Cisco IOS images and is the default location where the
switch gets its Cisco IOS at boot time.
■ NVRAM: Nonvolatile RAM (NVRAM) stores the initial or startup configuration file
that is used when the switch is first powered on and when the switch is reloaded.
Copying and Erasing Configuration Files
Initial Configuration (Setup Mode)
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