CCNA – Semester2
Module 5
Managing Cisco IOS Software
Objectives
• Router boot sequence and verification
• Identify the configuration register values
• Save and restore configuration files
• Save and restore IOS images

Router Boot Sequence and
Verification
Router Startup Sequence

Locating the Cisco IOS Software
Boot IOS from Flash Memory
• A system image from flash memory can be loaded. The
advantage is that information stored in flash memory is not
vulnerable to network failures.

Boot IOS from TFTP
• In case flash memory becomes corrupted, a system
image can be loaded from a TFTP server.
Boot IOS from ROM
• If flash memory is corrupted and the network server
fails to load the image, booting from ROM (if
available) is the final bootstrap option in software.

Configuration register
• The order in which the router looks for system
bootstrap information depends on the boot field
setting in the configuration register.
• The configuration register is a 16-bit register in
NVRAM.
Configuration register
• Use a hexadecimal number to express
configuration register value .
16-bit register
0x 0000 0000 0000 0000
6 3210
Bit: 16
• 0 – 3: Boot field
• 6: Ignore NVRAM contents
• 8: Break disabled
• 11-12: Console line speed
• 13: Boot ROM if network boot fails
• 15: Diagnostic and ignore NVRAM

Configuration register: Boot field (2)
• Router(config)# config-register 0x2102
• Router(config)# exit
• Router# show version
show version
Cisco Internetwork Operating System Software
IOS (tm) 2500 Software (C2500-D-L), Version 12.0(10), RELEASE SOFTWARE (fc1)
Copyright (c) 1986-2000 by cisco Systems, Inc.
Compiled Mon 20-Mar-00 22:33 by phanguye
Image text-base: 0x0303882C, data-base: 0x00001000
ROM: System Bootstrap, Version 11.0(10c), SOFTWARE
BOOTFLASH: 3000 Bootstrap Software (IGS-BOOT-R), Version 11.0(10c), RELEASE
SOFTWARE (fc1)
SGCTT-HCM uptime is 1 week, 1 day, 1 hour, 9 minutes
System restarted by power-on
System image file is \"flash:c2500-d-l.120-10\"
cisco 2500 (68030) processor (revision N) with 2048K/2048K bytes of memory.
Processor board ID 23101339, with hardware revision 00000000
Bridging software.
X.25 software, Version 3.0.0.
1 Ethernet/IEEE 802.3 interface(s)
2 Serial network interface(s)
32K bytes of non-volatile configuration memory.
8192K bytes of processor board System flash (Read ONLY)
Configuration register is 0x2102

The router boot process
ROM monitor
initializes
Boots the image
0 1
What is
Stays in ROM
in boot ROM
Boot
monitor field?
or boot flash
2 to F
yes no
Boot
commands
in NVRAM ?
Executes boot Router’s
commands Fallback sequence
Password Recovery
Start
Cold Boot router
Ctrl + Break
Within 60s
In 25xx routers In 26xx routers
o/r 0x2142 confreg 0x2142
i

Password Recovery
Initial
Config?
N
enable
Copy start run
Conf term
Enable secret cisco
Password Recovery
Config-register 0x2102
Ctrl-Z
Copy Run Start

Troubleshooting IOS boot failure
• In the event that the router does not boot properly,
there are several things that could be wrong:
– Configuration file has missing or incorrect boot system statement
– Incorrect configuration register value
– Corrupted flash image
– Hardware failure
Incorrect Boot System Statement
• Use the show running-config command and look
for a boot system statement near the top of the
configuration.
• If the boot system statement points to an
incorrect IOS image, delete the statement using
the “no” version of the command.

Incorrect configuration register value
• An incorrect configuration register setting will
prevent the IOS from loading from flash.
• The value in the configuration register tells the
router where to get the IOS.
• This can be confirmed by using the show version
command
Corrupted flash image
• If this is the case, an error message should be displayed
during boot. That message may take one of several forms.
Some examples are:
– 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 IOS should be uploaded
into the router.

Hardware failure
• If none of the above appears to be the problem,
the router could have a hardware failure.
• If this is the case, the Cisco Technical
Assistance (TAC) center should be contacted.
• Although hardware failures are rare, they do
occur.
Managing the Cisco File System

Software Components in Memory
• Routers and switches
depend on software for
their operation. The two
types of software
required are operating
systems and
configuration files.
Cisco IOS File System
• Beginning with version 12 of the IOS, a single interface
to all the file systems that a router uses is provided. This
is referred to as the Cisco IOS File System (IFS).
• The IFS provides a single method to perform all the file
system management that a router uses.
• This would include the flash memory file systems, the
network file systems (TFTP, rcp, and FTP), and reading
or writing data (such as NVRAM, the running
configuration, ROM).

IOS Version 12.x commands
• The IFS uses the URL
convention to specify
files on network
devices and the
network.
• The URL convention
identifies the location
of the configuration
files following the
colon as
[[[//location]/directory]
/filename]
IOS naming conventions

Managing configuration files using TFTP
Managing configuration files using copy and
paste
• Another way to create a backup copy of the
configuration is to capture the output of the
show running-config command
• Input configuration file using eather Hyper
Terminal-Send Text or Windows Buffer (Copy
and Paste)

Managing IOS images using TFTP
Environment variables
• The environmental variables provide a minimal
configuration to allow for the TFTP of the IOS.
• The ROMmon TFTP transfer works only on the
first LAN port so a simple set of IP parameters
are set for this interface.

Setting environment variables
• Start router and press Ctrl+Break
• Configure the environment variables
– IP_ADDRESS= {ip_address}
– IP_SUBNET_MASK={ip_subnet_mask}
– DEFAULT_GATEWAY={default_gateway}
– TFTP_SERVER={tftpserver_ip_address}
– TFTP_FILE={IOS_filename}
– set
– sync (save environment variables in NVRAM)
– tftpdnld
– reset (after download completed)
Summary
• Identifying stages of the router boot sequence
• Using the boot system command
• Identifying the configuration register settings
• Managing configuration files using copy-and-
paste
• Managing system files with TFTP

CCNA2 – Module5