C H A PT E R

Cisco IOS Basic Skills

Understanding how to use Cisco IOS software saves time when you are configuring your
router. If you need a refresher, take a few minutes to read this chapter. If you are already
familiar with Cisco IOS software, go to Chapter 3, Configuring Remote Office to
Corporate Office Networks or Chapter 4, Configuring Small Office to ISP Networks.
This chapter describes what you need to know before you begin configuring your Cisco 805
router with Cisco IOS software (the software that runs your router).
Note Cisco recommends that inexperienced network administrators use the Cisco 805

Fast Step software to configure their routers.

This chapter contains the following sections:

Configuring the Router from a PC

Understanding Command Modes
Getting Help
Enable Secret and Enable Passwords
Entering Global Configuration Mode

Cisco IOS Basic Skills 2-1

Configuring the Router from a PC

Using Commands
Saving Configuration Changes

Configuring the Router from a PC

You can configure your router from a connected PC. For information on how to connect the
PC, refer to the Cisco 805 Router Hardware Installation Guide.
After connecting the PC, you need terminal emulation software. The PC uses this software
to send commands to your router. Table 2-1 lists some common types of this software,
which are based on the type of PC you are using.
Table 2-1

Terminal Emulation Software

PC Operating System

Software

Windows 95, Windows 98, Windows NT

HyperTerm (included with Windows software),

ProComm Plus

Windows 3.1

Terminal (included with Windows software)

Macintosh

ProComm, VersaTerm (supplied separately)

You can use the terminal emulation software to change settings for the type of device that
is connected to the PC, in this case a router. Configure the software to the following
standard VT-100 emulation settings so that your PC can communicate with your router:

9600 baud
8 data bits
No parity
1 stop bit
No flow control

These settings should match the default settings of your router. To change the router baud,
data bits, parity, or stop bits settings, you must reconfigure parameters in the ROM monitor.
For more information, refer to Appendix A, ROM Monitor. To change the router flow
control setting, use the flowcontrol line configuration command.

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Cisco 805 Router Software Configuration Guide

Understanding Command Modes

For information on how to enter global configuration mode so that you can configure you
router, refer to the Entering Global Configuration Mode section later in this chapter.

Understanding Command Modes

This section describes the Cisco IOS command mode structure. Each command mode
supports specific Cisco IOS commands. For example, you can use the interface type
number command only from global configuration mode.
The following Cisco IOS command modes are hierarchical. When you begin a router
session, you are in user EXEC mode.

User EXEC
Privileged EXEC
Global configuration

Table 2-2 lists the command modes that are used in this guide, how to access each mode,
the prompt you see in that mode, and how to exit to a mode or enter the next mode. Because
each mode configures different router elements, you might need to enter and exit modes
frequently. You can see a list of available commands for a particular mode by entering a
question mark (?) at the prompt. For a description of each command, including syntax, refer
to the Cisco IOS 12.0 documentation set.

Cisco IOS Basic Skills 2-3

Understanding Command Modes

Table 2-2

Command Modes Summary

Mode

Access Method

Prompt

User EXEC

Begin a session with

your router.

Router>

Exit/Entrance
Method
To exit router session,
enter the logout
command.

About this Mode

Use this mode to:
Change terminal
settings.
Perform basic tests.
Display system
information.

Privileged
EXEC

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Enter the enable

command from user
EXEC mode.

Router#

Cisco 805 Router Software Configuration Guide

To exit to user EXEC

mode, enter the
disable command.

Use this mode to:

To enter global
configuration mode,
enter the configure
command.

Perform the verification

steps shown in this
guide.

Configure your router

operating parameters.

To prevent unauthorized
changes to your router
configuration, access to
this mode should be
protected with a
password as described in
Enable Secret and
Enable Passwords later
in this chapter.

Understanding Command Modes

Table 2-2

Command Modes Summary (continued)

Mode

Access Method

Prompt

Global
configuration

Enter the configure

command from
privileged EXEC mode.

Router
(config)#

Exit/Entrance
Method
To exit to privileged
EXEC mode, enter the
exit or end command,
or press Ctrl-Z.
To enter interface
configuration mode,
enter the interface
command.

About this Mode

Use this mode to configure
parameters that apply to
your router as a whole.
Also, you can access the
following modes, which
are described later in this
table:
Interface configuration
Router configuration
Line configuration

Interface
configuration

Enter the interface

command (with a
specific interface, such
as interface ethernet 0)
from global
configuration mode.

Router
(config-if)#

To exit to global
configuration mode,
enter the exit
command.

Use this mode to configure

parameters for the router
Ethernet and serial
interfaces or subinterfaces.

To exit to privileged
EXEC mode, enter the
end command, or
press Ctrl-Z.
To enter subinterface
configuration mode,
specify a subinterface
with the interface
command.

Router
configuration

Enter your router

command followed by
the appropriate keyword,
for example router rip,
from global
configuration mode.

Router
(configrouter)#

To exit to global
configuration mode,
enter the exit
command.

Use this mode to configure

an IP routing protocol.

To exit to privileged
EXEC mode, enter the
end command, or
press Ctrl-Z.

Cisco IOS Basic Skills 2-5

Getting Help

Table 2-2

Command Modes Summary (continued)

Mode

Access Method

Prompt

Line
configuration

Specify the line

command with the
desired keyword, for
example, line 0, from
global configuration
mode.

Router
(configline)#

Exit/Entrance
Method
To exit to global
configuration mode,
enter the exit
command.

About this Mode

Use this mode to configure
parameters for the terminal
line.

To enter privileged
EXEC mode, enter the
end command, or
press Ctrl-Z.

Getting Help
You can use the question mark (?) and arrow keys to help you enter commands.
For a list of available commands at that command mode, enter a question mark:
router> ?
access-enable
access-profile
clear
...

Create a temporary access-list entry

Apply user-profile to interface
Reset functions

To complete a command, enter a few known characters followed by a question mark (with
no space):
router> s?
* s=show set show slip systat

For a list of command variables, enter the command followed by a space and a question
mark:
router> show ?
clock
Display the system clock
dialer
Dialer parameters and statistics
exception
exception information
...

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Cisco 805 Router Software Configuration Guide

Enable Secret and Enable Passwords

To redisplay a command you previously entered, press the up-arrow key. You can continue
to press the up arrow key for more commands.

Enable Secret and Enable Passwords

By default, the router ships without password protection. Because many privileged EXEC
commands are used to set operating parameters, you should password-protect these
commands to prevent unauthorized use.
You can use two commands to do this:

enable secret <password> (a very secure, encrypted password)

enable <password> (a less secure, unencrypted password)

You must enter an enable secret password to gain access to privileged EXEC mode
commands.
For maximum security, the passwords should be different. If you enter the same password
for both during the setup process, your router accepts the passwords, but warns you that
they should be different.
An enable secret password can contain from 1 to 25 uppercase and lowercase
alphanumeric characters. An enable password can contain any number of uppercase and
lowercase alphanumeric characters. In both cases, a number cannot be the first character.
Spaces are also valid password characters; for example, two words is a valid password.
Leading spaces are ignored; trailing spaces are recognized.
If you lose or forget your enable password, refer to Appendix E, Recovering a Lost Enable
Password.

Entering Global Configuration Mode

To make any configuration changes to your router, you must be in global configuration
mode. This section describes how to enter global configuration mode while using a terminal
or PC that is connected to your router Console port.

Cisco IOS Basic Skills 2-7

Using Commands

To enter global configuration mode:

Step 1

After your router boots up, answer no when the following question displays:
Would you like to enter the initial configuration dialog [yes]: no

Step 2

Enter the enable command:

router> enable

Step 3

If you have configured your router with an enable password, enter it when you
are prompted.
The enable password does not show on the screen when you enter it. This
example shows how to enter privileged EXEC mode:
Password: <enable_password>
router#

Enable mode is indicated by the # in the prompt. You can now make changes to
your router configuration.
Step 4

Enter the configure terminal command to enter global configuration mode,

indicated by (config)# in the prompt:
router# configure terminal
router (config)#

You can now make changes to your router configuration.

Using Commands
This section provides some tips about entering Cisco IOS commands at the command-line
interface (CLI).

Abbreviating Commands
You only have to enter enough characters for the router to recognize the command as
unique. This example shows how to enter the show version command:
router # sh v

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Cisco 805 Router Software Configuration Guide

Undoing Commands

Undoing Commands
If you want to disable a feature or undo a command you entered, you can enter the keyword
no before most commands; for example, no ip routing.

Command-Line Error Messages

Table 2-3 lists some error messages that you might encounter while using the CLI to
configure your router.
Table 2-3

Common CLI Error Messages

Error Message

Meaning

How to Get Help

% Ambiguous command:
"show con"

You did not enter enough characters

for your router to recognize the
command.

Reenter the command followed by a

question mark (?) with no space
between the command and the
question mark.
The possible keywords that you can
enter with the command are
displayed.

% Incomplete command.

You did not enter all of the keywords

or values required by this command.

Reenter the command followed by a

question mark (?) with no space
between the command and the
question mark.
The possible keywords that you can
enter with the command are
displayed.

% Invalid input detected at

^ marker.

You entered the command

incorrectly. The error occurred where
the caret mark (^) appears.

Enter a question mark (?) to display

all of the commands that are
available in this command mode.

Cisco IOS Basic Skills 2-9

Saving Configuration Changes

Saving Configuration Changes

You need to enter the copy running-config startup-config command to save your
configuration changes to nonvolatile RAM (NVRAM) so that they are not lost if there is a
system reload or power outage. This example shows how to use this command to save your
changes:
router # copy running-config startup-config
Destination filename [startup-config]?

Press the Return key to accept the default destination filename startup-config, or enter your
desired destination filename and press the Return key.
It might take a minute or two to save the configuration to NVRAM. After the configuration
has been saved, the following message appears:
Building configuration...
router #

Summary
Now that you have reviewed some Cisco IOS software basics, you can begin to configure
your router. Remember:

You can use the question mark (?) and arrow keys to help you enter commands.

If you want to disable a feature, enter the keyword no before the command; for example,
no ip routing.

Save your configuration changes to NVRAM so that they are not lost if there is a system
reload or power outage.

Each command mode restricts you to a set of commands. If you are having difficulty
entering a command, check the prompt, and then enter the question mark (?) for a list
of available commands. You might be in the wrong command mode or using the wrong
syntax.

Where to Go Next
To begin configuring your router, go to either Chapter 3, Configuring Remote Office to
Corporate Office Networks or Chapter 4, Configuring Small Office to ISP Networks.

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