Troubleshooting Cisco IOS Software 579
Troubleshooting Cisco IOS Software
Several things could prevent the router from booting properly:
■ Configuration file with a missing or incorrect boot system statement
■ Incorrect configuration register value
■ Corrupted Flash image
■ Hardware failure
When the router boots, it looks in the configuration file for a boot system statement.
This statement can force the router to boot from another image instead of the Cisco
IOS Software image in Flash. To identify the boot image source, type the show version
command and look for the line that identifies the image boot source, as shown in
Example 11-18.
An incorrect configuration register setting prevents the Cisco IOS Software from loading
from Flash memory. The value in the configuration register tells the router where to
get the Cisco IOS Software image. This can be confirmed by using the show version
command and looking at the last line for the configuration register, as shown in
Example 11-19.
The correct value varies in different hardware platforms. The Cisco IOS Software doc-
umentation should include a printed copy of the show version output. If that docu-
mentation is not available, there are resources on the Cisco Documentation CD or at
Cisco.com to identify the correct configuration register value. Correct this by changing
the configuration register in the configuration and saving this as the startup configuration.
Example 11-18 Image Boot Source
Cisco> show version
output omitted
ROM: System Bootstrap, Version 11.0(10c), SOFTWARE
BOOTLDR: 3000 Bootstrap Software (IGS-BOOT-R), Version 11.0(10c), RELEASE
SOFTWARE (fc1)
Example 11-19 Configuration Register
Cisco> show version
output omitted

Configuration register is 0x2102
3000 Bootstrap Software (IGS-BOOT-R), Version 11.0(10c)
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580 Chapter 11: Router Fundamentals
If there is still a problem, the router might have a corrupted Flash image file. If this is
the case, an error message should be displayed during boot. The error message might
display as follows:
open: read error requested 0x4 bytes, got 0x0
trouble reading device magic number
boot: cannot open "flash:"
boot: cannot determine first file name on device "flash:"ú
If the Flash image is corrupt, a new Cisco IOS Software image should be uploaded into
the router. If the problem has not been identified in this section, the router could have
a hardware failure. If this is the case, you should contact the Cisco Technical Assistance
Center (TAC). Although hardware failures are rare, they do occur.
Table 11-4 lists and describes other helpful router status commands. You can obtain a
list of all show commands by entering the show command followed by a space and a
question mark.
Table 11-4 Router Status Commands
Command Description
show version Displays the configuration of the system
hardware, the software version, the names
and sources of configuration files, and the
boot images, and displays the reason for the
last system reboot.
show processes Displays information about the active
processes.
show protocols Displays the configured protocols. This com-
mand shows the status of any configured
Layer 3 (network layer) protocol.

show memory Shows statistics about the router’s memory,
including memory-free pool statistics.
show stacks Monitors the stack use of processes and
interrupt routines.
show buffers Provides statistics for the buffer pools on the
router.
show flash Shows information about the Flash memory
device.
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Summary 581
Summary
The keys points discussed in this chapter were the following:
■ Establishing a HyperTerminal session
■ Logging into the router
■ Using the help feature in the command-line interface
■ Using enhanced editing commands
■ Using command history
■ Troubleshooting command errors
■ The router can boot into either ROM monitor, boot ROM, or Cisco IOS mode.
■ The show version and show flash commands provide information on Cisco IOS
Software and configuration register settings currently on the router.
■ Router commands are entered at the command-line interface (CLI) in either user
EXEC, privileged EXEC, global configuration, or specific configuration mode.
To supplement all that you’ve learned in this chapter, refer to the chapter-specific Videos,
PhotoZooms, and e-Lab Activities on the CD-ROM accompanying this book.
show running-config (write term on
Cisco IOS Software Release 10.3 or
earlier)
Displays the active configuration file.
show startup-config (show config

on Cisco IOS Software Release
10.3 or earlier)
Displays the backup configuration file.
show interface Displays statistics for all interfaces configured.
Table 11-4 Router Status Commands (Continued)
Command Description
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582 Chapter 11: Router Fundamentals
Key Terms
Cisco Internetwork Operating System (IOS) Software Software stored as an image
file in Flash memory on the router that, when loaded into RAM, provides the operat-
ing system that runs the router.
command-line interface (CLI) An interface that enables the user to interact with
the operating system by entering commands and optional arguments.
daughter card Similar to an expansion board, but it accesses the motherboard
components (memory and CPU) directly instead of sending data through the slower
expansion bus.
Flash memory A special type of EEPROM that can be erased and reprogrammed
in blocks instead of 1 byte at a time. Many modern PCs have their BIOS stored on a
Flash memory chip so that it can be updated easily, if necessary. Flash memory is also
popular in modems because it enables the modem manufacturer to support new protocols
as they become standardized.
light-emitting diode (LED) Semiconductor device that emits light produced by
converting electrical energy. Status lights on hardware devices are typically LEDs.
nonvolatile RAM (NVRAM) RAM that retains its contents when a unit is powered off.
power-on self-test (POST) Set of hardware diagnostics that runs on a hardware
device when that device is powered up.
Check Your Understanding
Complete all the review questions to test your understanding of the topics and con-
cepts in this chapter. Answers are listed in Appendix C, “Check Your Understanding

Answer Key.”
1. A router initializes by doing which of the following?
A. Loading the NVRAM, the setup procedure, and the operating system
B. Loading the bootstrap, the operating system, and a configuration file
C. Loading the bootstrap, the setup procedure, and the operating system
2. During the setup process in a router, what keys can be used to escape the
sequence?
A. Ctrl-A
B. Ctrl-E
C. Ctrl-C
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Check Your Understanding 583
3. Match the configuration setting on the right with the items on the left that are
needed to establish a HyperTerminal session:
A. BAUDNone
B. DATA BITS1
C. PARITY8
D. STOP BITSNone
E. FLOW CONTROL9600
4. Which of the following is true at initial boot-up output?
A. The Cisco IOS Software version that the router uses can be seen.
B. The Cisco IOS Software version that the router uses cannot be seen.
5. Which of the following is true at initial boot-up output?
A. The amount of Flash memory can be seen.
B. The amount of Flash memory cannot be seen.
6. Match the commands on the left with the correct descriptions on the right.
Ctrl + a Moves out of configuration mode
Ctrl + b Moves to the end of the command line
Ctrl + e Moves back one word
Ctrl + f Moves to the beginning of the command line

Esc + b Moves forward one character
Esc + f Moves forward one word
Ctrl + a Moves back one character
7. Match the commands on the left with the correct descriptions on the right.
Tab Enables advanced editing
Ctrl + p Sets the command buffer size
Ctrl + n Recalls the most recent command
show history Shows the command buffer
terminal history size # Recalls the last command
terminal editing Completes the entry
no Terminal editing Disables advanced editing features
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584 Chapter 11: Router Fundamentals
8. What are the major elements of a typical router configuration?
A. Passwords, interfaces, routing protocols, DNS
B. Boot sequence, interfaces, TFTP server, NVRAM
C. NVRAM, ROM, DRAM, interfaces
D. Interfaces, routing protocols, configuration register, Flash memory
9. Which of the following correctly describes a method for specifying how a router
loads the Cisco IOS Software?
A. Designate fallback sources for the router to use in sequence from NVRAM.
B. Configure the Cisco IOS software image for the location where it will
bootstrap.
C. Manually boot a default system image at a virtual terminal.
D. Manually boot a default system image at the network server.
10. Which of the following is not a boot option that can be set with the configura-
tion register boot field?
A. Cisco IOS Software boots in ROM monitor mode.
B. Cisco IOS Software automatically boots from ROM.
C. Cisco IOS Software automatically boots from a TFTP server.

D. NVRAM is examined for boot system commands.
11. Which of the following is information displayed by the Cisco IOS Software
show version command?
A. Detailed statistics about each page of the router’s memory
B. The name of the system image
C. The names and sizes of all files in Flash memory
D. The status of configured network protocols
12. Which of the following has a limited version of router Cisco IOS Software?
A. ROM
B. Flash memory
C. TFTP server
D. Bootstrap
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Check Your Understanding 585
13. If you want to completely back out of configuration mode, which of the follow-
ing must you enter?
A. Exit
B. no config-mode
C. Ctrl + e
D. Ctrl + z
14. If you are planning to configure an interface, what prompt should be on the
router?
A. router(config)#
B. router(config-in)#
C. router(config-intf)#
D. router(config-if)#
15. What is the acronym used to describe a Cisco router’s text-based user interface?
A. CLI
B. TCP/IP
C. OSPF

D. OSI
16. What two modes of access to router commands exist for Cisco routers?
A. User and privileged
B. User and guest
C. Privileged and guest
D. Guest and anonymous
17. Which mode do you use to make router configuration changes on Cisco routers?
A. User
B. Privileged
C. Administrator
D. Root
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Objectives
Upon completion of this chapter, you will be able to
■ Name a router
■ Set passwords
■ Examine show commands
■ Configure a serial interface
■ Configure an Ethernet interface
■ Execute changes to a router
■ Save changes to a router
■ Configure an interface description
■ Configure a message-of-the-day banner
■ Configure host tables
■ Describe backup documentation
■ Recover passwords
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Chapter 12
Router Configuration
This chapter covers the router modes and configuration methods to update a router’s con-

figuration file. It is important to have a firm understanding of Cisco IOS Software and
know the procedures for starting a router. In addition, this chapter describes the tasks
necessary for password recovery.
Please be sure to look at this chapter’s e-Labs, Videos, and PhotoZooms that you will find
on the CD-ROM accompanying this book. These CD elements are designed to supple-
ment the material and reinforce the concepts introduced in this chapter.
Command-Line Interface Command Modes
To gain access to a router, a login is required. After login, there is a choice of modes. The
modes interpret the commands that are typed and carry out the operations. Two EXEC
modes exist:
■ User mode
■ Privilege mode (or enable mode)
The following sections define the two command modes and their associated commands.
User Command List
A user is automatically in user EXEC mode upon first login to the router. User mode is a
limited examination of the router. Table 12-1 provides the user mode commands and
their descriptions.
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588 Chapter 12: Router Configuration
Table 12-1 User ModeCommands
Command Description
access-enable Creates a temporary access list entry
atmsig Executes ATM signaling commands
cd Changes current device
clear Resets functions
connect Opens a terminal connection
dir Lists files on a given device
disable Turns off privileged commands
disconnect Disconnects an existing network
enable Turns on privileged commands

exit Exits EXEC
help Gets a description of the interactive help system
lat Opens a LAT connection
lock Locks the terminal
login Logs in as a particular user
logout Exits EXEC mode
mrinfo Requests neighbor and version information from a multicast
router
mstat Shows statistics after multiple multicast traceroutes
mtrace Traces the reverse multicast path from destination to source
name-connection Names an existing network connection
pad Opens an X.29 PAD connection
ping Sends echo messages
ppp Starts IETF Point-to-Point Protocol (PPP)
pwd Displays current device
resume Resumes an active network connection
rlogin Opens an rlogin connection
N
O
TE
At this point, the
list of commands
displayed is context
sensitive. You see a
different list when
you are in user mode
versus enable mode,
and when in global
configuration mode
versus configure inter-

face modes.
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