Cisco's internetwork operating system (IOS) software
platform is implemented on the varied hardware discussed in this book. IOS
software delivers network services and enables networked applications. It
is the embedded software architecture in all of the Cisco routers, and it
is also the operating system of the Catalyst 1900 enterprise series switches.
Cisco IOS enables network services in these products, including
Features to carry the chosen network protocols and functions
Connectivity to provide high-speed traffic between devices
Security to control access and discourage unauthorized network
Scalability to add interfaces and capability as the need for
Reliability to ensure dependable access to networked resources
A Cisco IOS command-line interface (CLI) can be accessed through a console
connection, modem connection, or Telnet session. Regardless of which connection
method is used, access to the IOS command-line interface is generally referred
to as an EXEC session.
You will learn to use the Cisco IOS software to communicate the configuration
details for the switches and routers discussed in this book. The purpose here
is to help facilitate the knowledge transfer for configuring Cisco devices.
Back on the job, you can use this knowledge to support a configuration that
will reflect the policy of functions and authorizations that are required
by your organization.
Protocol addresses and parameters will be guided by the objectives of
this book and will be structured to help you understand internetworking. Back
on the job, address and related parameters will reflect legal addressing and
the protocol requirements of your company.
When you start the Catalyst switch for
the first time, it uses an initial configuration with default settings.
When you start the Cisco router for the first time, it does not have
an initial configuration. The router software will prompt you for a minimum
of details using an optional dialog called Setup.
You will set up a minimum device configuration for the router and the
switch in this chapter. Changes to these minimum or default configurations
constitute much of your network administrator tasks. Most of these configuration
changes will occur later in this book.
When the Catalyst switch or Cisco
router starts up, three main operations are performed on the networking device:
The device finds the hardware and performs hardware-checking
routines. A term often used to describe this initial set of routines is power-on self test
After the hardware has been shown to be in good working
order, the devices perform system startup routines. These routines initiate
the switch or router by locating and loading the operating system software.
After the operating system is loaded, the devices try
to find and apply software configuration settings that establish the details
needed for network operation.
There is typically a sequence of fallback routines that provide software
startup alternatives if needed.
In the next several pages of this chapter, you will learn about and
practice using these three main operations. You will start up the switch first,
and then the router.
The switch and the router can be configured from many locations:
Upon initial installation, the network administrator typically
configures the networking devices from the console terminal, which is connected
via the console port.
If the administrator is supporting remote devices, a local
modem connection at the device's auxiliary port permits the administrator
to configure the network devices.
For selected routers and switches, a CD-ROM can provide a
rapid configuration application, such as Cisco Fast Step, to make the most
simple configuration tasks easier to accomplish.
After initial startup, there are additional external sources for software
that connect to device interfaces:
Devices with established IP addresses can allow Telnet connections
for configuration work.
Download a configuration file from a Trivial File Transfer
Protocol (TFTP) server.
Configure the device via a Hypertext Transfer Protocol (HTTP)
All three of the methods just mentioned assume an active IP configuration
and network connectivity to the device.
Cisco IOS software uses a command-line interface as its traditional
console environment. Although Cisco IOS software is a core technology that
extends across many products, Cisco IOS operation details vary on different
To enter commands into the user interface, you type your entries within
one of several console command modes. Each command mode is indicated by a
Cisco IOS software uses a hierarchy of commands in its command-mode
structure. Each command mode supports specific Cisco IOS commands related
to a type of operation on the device.
As a security feature, Cisco IOS separates EXEC sessions into two different
default access levels: user EXEC level and privileged EXEC level.
User EXEC level lets you access only a limited number of basic
Privileged EXEC level lets you access all router commands (for
example, configuration and management). It can be password-protected to allow
only authorized users to configure or maintain the router.
The Enter key instructs the device to parse and execute the command.
For example, when an EXEC session is started, the router will display
a hostname> prompt. The right arrow (>) in the prompt indicates that the router is at
the user EXEC level.
The user EXEC level does not contain any commands that might allow the
user to control the operation of the router (for example, reload or configure).
To list the commands available at the user EXEC level, type a
question mark (?)
at the hostname> prompt. (This feature
is referred to as context-sensitive help.)
Critical commands (for example, configuration, management, and debugging)
require that the user be at the privileged EXEC level. Privileged EXEC mode
provides the user with a detailed examination of a switch or router.
To change to the privileged EXEC level, type enable
at the hostname> prompt. If an enable password or enable
secret password is configured, the switch or router will then prompt
you for that password.
When the correct enable password
is entered, the switch or router prompt will change to hostname#,
indicating that the user is now at the privileged EXEC level.
Typing a question mark (?)
at the privileged EXEC level will reveal many more command options than those
available at the user EXEC level. To return to the user EXEC level, type disable at the hostname#