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Appendix A      Cisco IOS Basic Skills
Understanding Command Modes
Table A-2 Command Modes Summary
Mode Access Method PromptExit/Entrance 
Method About this Mode
User EXEC Begin a session with 
your router.
Router>To exit router 
session, enter the 
logout command. Use this mode to:
Change terminal 
settings.
Perform basic tests.
Display system 
information.
Privileged 
EXECEnter the enable 
command from user 
EXEC mode.
Router#To exit to user 
EXEC mode, enter 
the disable 
command.
To enter global 
configuration 
mode, enter the 
configure 
command.Use this mode to:
Configure your 
router operating 
parameters. 
Perform the 
verification steps 
shown in this guide.
To  p r e v e n t  
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.
Global 
configurationEnter the configure 
command from 
privileged EXEC 
mode.
Router 
(config)#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.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 
						

							  
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Getting Help
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-enableCreate a temporary access-list entry
access-profileApply user-profile to interface
clearReset 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
Interface 
configurationEnter 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.
To exit to privileged 
EXEC mode, enter 
the end command, 
or press Ctrl-Z. 
To  e n t e r  
subinterface 
configuration 
mode, specify a 
subinterface with 
the interface 
command.Use this mode to 
configure parameters 
for the router Ethernet 
and serial interfaces or 
subinterfaces.
Router 
configurationEnter your router 
command followed by 
the appropriate 
keyword, for example 
router rip, from 
global configuration 
mode.
Router 
(config- 
router)#To exit to global 
configuration 
mode, enter the exit 
command.
To exit to privileged 
EXEC mode, enter 
the end command, 
or press Ctrl-Z. Use this mode to 
configure an IP routing 
protocol.
Line 
configurationSpecify the line 
command with the 
desired keyword, for 
example, line 0, from 
global configuration 
mode.
Router 
(config- 
line)#To exit to global 
configuration 
mode, enter the exit 
command.
To enter privileged 
EXEC mode, enter 
the end command, 
or press Ctrl-Z.Use this mode to 
configure parameters 
for the terminal line.
Table A-2 Command Modes Summary (continued)
Mode Access Method PromptExit/Entrance 
Method About this Mode 
						

							  
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Appendix A      Cisco IOS Basic Skills
Enable Secret and Enable Passwords
For a list of command variables, enter the command followed by a space and a question mark:
router> show ?
clock Display the system clock
dialerDialer parameters and statistics
exceptionexception information
...
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)
Yo u  m u s t  e n t e r  a n  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. 
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.
To enter global configuration mode:
Step 1After your router boots up, answer no when the following question displays: 
Would you like to enter the initial configuration dialog [yes]: no
Step 2Enter the enable command:
router> enable
Step 3If 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. 
						

							  
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Using Commands
Step 4Enter 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
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
Ta b l e A - 2 lists some error messages that you might encounter while using the CLI to configure your 
router. 
						

							  
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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 Return to accept the default destination filename startup-config, or enter your desired destination 
filename and press Return.
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.
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. 
Table A-3 Common CLI Error Messages
Error Message Meaning How to Get Help
% Ambiguous command: 
show conYou 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. 
						

							  
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Where to Go Next
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.
Where to Go Next
To configure your router, go to Chapter 3, “Basic Router Configuration,” and Chapter 4, “Advanced 
Router Configuration.” 
						

							  
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APPENDIXB
ROM Monitor
This appendix describes the ROM monitor (also called the bootstrap program). The ROM monitor 
firmware runs when the router is powered up or reset. The firmware helps to initialize the processor 
hardware and boot the operating system software. You can use the ROM monitor to perform certain 
configuration tasks, such as recovering a lost password or downloading software over the console port. 
If there is no Cisco IOS software image loaded on the router, the ROM monitor runs the router.
This appendix contains the following sections:
Entering the ROM Monitor
ROM Monitor Commands
Command Descriptions
Disaster Recovery with TFTP Download
Configuration Register
Console Download
Debug Commands
Exiting the ROM Monitor
Entering the ROM Monitor
To use the ROM monitor, you must be using a terminal or PC that is connected to the router over the 
console port. Refer to documentation listed in the Obtaining Documentation section of this guide for 
information on connecting your router to a PC or terminal.
Perform these steps to configure the router to boot up in ROM monitor mode the next time it is rebooted.
Command Purpose
Step 1enableIf an enable password is configured, enters the 
enable command and the enable password to 
enter privileged EXEC mode.
Step 2configure terminalEnters global configuration mode.
Step 3config-reg 0x0Resets the configuration register. 
						

							  
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Appendix B      ROM Monitor
ROM Monitor Commands
TimesaverBreak (system interrupt) is always enabled for 60 seconds after the router reboots, regardless of whether 
it is set to on or off in the configuration register. During this 60-second window, you can break to the 
ROM monitor prompt by pressing the Break key. 
ROM Monitor Commands
Enter ? or help at the ROM monitor prompt to display a list of available commands and options, as 
follows:
rommon 1 > ?alias               set and display aliases command
boot                boot up an external process
break               set/show/clear the breakpoint
confreg             configuration register utility
cont                continue executing a downloaded image
context             display the context of a loaded image
cookie              display contents of cookie PROM in hex
dev                 list the device table
dir                 list files in file system
dis                 display instruction stream
dnld                serial download a program module
frame               print out a selected stack frame
help                monitor builtin command help
history             monitor command history
meminfo             main memory information
repeat              repeat a monitor command
reset               system reset
set                 display the monitor variables
stack               produce a stack trace
sync                write monitor environment to NVRAM
sysret              print out info from last system return
tftpdnld            tftp image download
unalias             unset an alias
unset               unset a monitor variable
xmodem              x/ymodem image download
Step 4exitExits global configuration mode.
Step 5reloadReboots the router with the new configuration 
register value. The router remains in ROM 
monitor and does not boot the Cisco IOS 
software.
As long as the configuration value is 0x0, you 
must manually boot the operating system from 
the console. See the boot command in the 
“Command Descriptions” section in this 
appendix. 
After the router reboots, it is in ROM monitor 
mode. The number in the prompt increments with 
each new line. Command Purpose 
						

							  
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Appendix B      ROM Monitor
Command Descriptions
Commands are case sensitive. You can halt any command by pressing the Break key on a terminal. If 
you are using a PC, most terminal emulation programs halt a command when you press the Ctrl and the 
Break keys at the same time. If you are using another type of terminal emulator or terminal emulation 
software, refer to the documentation for that product for information on how to send a Break command. 
Command Descriptions
Ta b l e B - 1 describes the most commonly used ROM monitor commands.
Disaster Recovery with TFTP Download
The standard way to load new software on your router is using the copy tftp flash privileged EXEC 
command from the Cisco IOS software command-line interface (CLI). However, if the router is unable 
to boot the Cisco IOS software, you can load new software while in ROM monitor mode.
Table B-1 Most Commonly Used ROM Monitor Commands
Command Description
help or ?Displays a summary of all available ROM monitor commands.
-?Displays information about command syntax; for example:
rommon 16 > dis -?
usage : dis [addr] [length]
The output for this command is slightly different for the xmodem download 
command:
rommon 11 > xmodem -?
xmodem: illegal option -- ?
usage: xmodem [-cyrxu] 
-c  CRC-16
-y  ymodem-batch protocol
-r  copy image to dram for launch
-x  do not launch on download completion
-u  upgrade ROMMON, System will reboot after upgrade
reset or iResets and initializes the router, similar to a power up.
devLists boot device identifications on the router; for example:
rommon 10> dev
Devices in device table:
        id  name
    flash:  flash 
dir device:Lists the files on the named device; for example, Flash files:
rommon 4 > dir flash:
      File size           Checksum   File name
2835276 bytes (0x2b434c)   0x2073    c806-oy6-mz
boot commands For more information about the ROM monitor boot commands, refer to the 
Cisco IOS Configuration Guide and the Cisco IOS Command Reference.
bBoots the first image in Flash memory.
b flash: [filename] Attempts to boot the image directly from the first partition of Flash memory. If 
you do not enter a filename, this command will boot this first image in Flash. 
						

							  
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Appendix B      ROM Monitor
Disaster Recovery with TFTP Download
This section describes how to load a Cisco IOS software image from a remote TFTP server to the router 
Flash memory. Use the tftpdnld command only for disaster recovery because it erases all existing data 
in Flash memory before downloading a new software image to the router.
TFTP Download Command Variables
This section describes the system variables that can be set in ROM monitor mode and that are used 
during the TFTP download process. There are both required variables and optional variables. 
NoteThe commands described in this section are case sensitive and must be entered exactly as shown.
Required Variables
These variables must be set with these commands before using the tftpdnld command:
Variable Command
IP address of the router.IP_ADDRESS= ip_address
Subnet mask of the router.IP_SUBNET_MASK= 
ip_address
IP address of the default gateway of the 
router.DEFAULT_GATEWAY= 
ip_address
Variable Command
IP address of the TFTP server from which the 
software will be downloaded.TFTP_SERVER= ip_address
The name of the file that will be downloaded 
to the router.TFTP_FILE= filename