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Managing Cisco IOS Software. CCNA2 v3.0 – Modul 5. Test the router hardware. Bootstrap. Flash. TFTP. ROM. Find and load the Cisco IOS software into RAM. NVRAM. TFTP. Console. Find and apply configuration statements, including protocol functions and interface addresses.

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Managing Cisco IOS Software

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managing cisco ios software

Managing Cisco IOS Software

CCNA2 v3.0 – Modul 5

stages of the router power on boot sequence

Test the router hardware





Find and load the Cisco IOS software into RAM




  • Find and apply configuration statements, including protocol functions and interface addresses
Stages of the Router Power-on Boot Sequence


Cisco Internetwork Operating System

Configuration File

how a cisco device locates and loads ios

Hexadecimal number

How a Cisco Device Locates and Loads IOS


configure terminal


Boot system flash c4500-p-mz_111-18.bin

The router uses boot system commands saved in NVRAM to locate the IOS.

Different settings in the configuration register enable the several alternatives:


Boot system tftp c4500-1.bin


Boot system rom




copy running-config startup-config

After it is reloaded, the router will try these commands in the order they were entered.

The order in which the router looks for system bootstrap information depends on the boot field setting in the configuration register. The default configuration register setting can be changed with the following command:

Router(config)#config-register 0x2142

configuration register boot field

The lowest four bits of the configuration register form the boot field.

Configuration register is 0x2102

Configuration Register – Boot Field


show version

..<output omitted>..

Configuration register is 0x2102

To view the current values of the configuration register:

The configuration register is a 16-bit register in NVRAM.

Note: the notation 0x informs us that the following number is a hexadecimal number.

From the example, Hex 2142 is 0010.0001.0000.0010 in binary.

Enter ROM monitor mode on reload.

Boot automatically from ROM.

Use boot system commands in NVRAM, this is the default.

troubleshooting ios boot failure
Troubleshooting IOS Boot Failure

On boot the router checks the configuration file for a boot system statement.

Boot problems are typically caused by any of the following:

  • Configuration file has missing or incorrect boot system statement
  • Incorrect configuration register value
  • Corrupted flash image
  • Hardware failure

To identify the boot image source:


show version

Cisco Internetwork Operating System Software

IOS (tm) C2600 Software (C2600-D-M), Version 12.2(16a), RELEASE SOFTWARE (fc2) ..<output omitted>..

ROM: System Bootstrap, Version 12.1(3r)T2, RELEASE SOFTWARE (fc1) Router uptime is 1 minute

System returned to ROM by power-on

System image file is "flash:c2600-d-mz.122-16a.bin"

troubleshooting ios boot failure6
Troubleshooting IOS Boot Failure

If the router has a corrupted flash image file an error message should be displayed during boot.

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.

The router could have a hardware failure.

If so, the Cisco TAC should be contacted.

ios file system overview

The two types of software required are _________________ and _____________.

  • The ___________ is software that allows the hardware to function as a router or switch.
  • The configuration contains the “instructions” that define how the device is to _________________.
  • A ____________________ creates the configuration that defines the desired functionality of the Cisco device.    
  • The IOS is stored in a memory area called _______.
  • The flash allows the IOS to be _________ or stores _____________ files.
  • The IOS is copied into and run from ______.
  • A copy of the configuration file is stored in ________.
  • This is referred to as the “______________”.
  • The startup configuration is copied into RAM at _________.
  • This configuration in RAM is the configuration used to _______ the router.
  • It is referred to as the “_____________”.
  • Beginning with version 12, the ______________________ provides a single method to perform all file system management.
  • The IFS uses ______ to specify files on network devices and the network.

operating system

IOS File System Overview


Cisco IOS®

route or switch

network administrator



multiple IOS




boot time



Cisco IOS File System


ios naming convention


Feature Set

Binary file

Located in Flash

File Format

IOS Version number

IOS Naming Convention

System image file is "flash:c2600-d-mz.122-16a.bin"

  • Examples of feature-set categories are:
  • Basic
  • Plus
  • Encryption (designated by ‘k8’ or ‘k9’ in IOS 12.2 and later)

The file format specifies if the IOS is compressed in flash and if the IOS is relocatable.

A relocatable image is copied from flash into RAM to run.

A non-relocatable image is run directly from flash.

As Cisco develops newer versions of the IOS, the numerical version number increases.

managing configuration files using tftp
Managing configuration files using TFTP

My# copy running-config tftp

Remote host []?

Name of configuration file to write[my-config]? My2

Write file My2 to ? [confirm] y

Writing My2

To store the current configuration on a network TFTP server enter the following command:

!!!!!!!!!!!!!!!!!!!! [OK]

A configuration file stored on one of the network servers can be used to configure a router:

Router# copy tftp running-config

Host or network configuration file [host]?

IP address of remote host[]?

Name of configuration file [Router-config] ? My2

Configure using My2 from [confirm] y

Booting My2 from

!!!!!! [OK-180/16000 bytes]

managing configuration files using capture and send
Managing Configuration Files using Capture and Send

To capture the configuration from HyperTerminal to a text file:

  • Select Transfer Capture Text
  • Specify a name for the text file to capture the output to
  • Select Start to start capturing text

Now all that appears on the screen will be written to the text file.

  • Display the configuration with a show running-config
  • To stop the capture select TransferCapture Text Stop

After the capture is complete, the configuration file needs to be edited to remove extra text, to add commands or to add comments with a !.

HyperTerminal can be used to restore a configuration. The edited backup of the configuration can be copied into the router:

  • Enter router global configuration mode.
  • From HyperTerminal, click on Transfer > Send Text File.
  • Select the name of the saved configuration file.
  • The lines of the file will be entered into the router as if they were being typed at the CLI. Observe any errors.
managing ios images using tftp
Managing IOS Images using TFTP

Occasionally the router will need to have the IOS upgraded or restored. On a new router the IOS should be backed up.


copy tftp flash

Address or name of remote host []?

Source filename []?


Destination filename [c2600-d-mz.122-16a.bin]?

Accessing tftp://

Erase Flash: before copying? [confirm]

Erasing the flash file system will remove all files

Continue? [confirm]

Erasing device



Loading c2600-d-mz.122-16a.bin from (via FastEthernet 0/0):


Verifying checksum

.. .. .. ..OK

[OK 8906598 bytes]

8906598 bytes copied in 270.12 secs


Recovering IOS Images

  • Check to see if an image is available in flash:

rommon 1>

dir flash:

  • If a valid image is present try to boot it:

To identify why the IOS image did not load from flash:

rommon 1>

boot flash:c2600-is-mz.121-5

  • If router now boots properly check the configuration register:


show version

  • If the configuration register value is correct check for boot system commands:


show startup-config

If the router will not properly boot from the image or there is no IOS image, a new IOS will need to be downloaded.

The IOS file may be recovered using either:

  • Xmodem to restore the image through the console
  • TFTP from the rommon mode
download using xmodem from rommon
Download using Xmodem from rommon >

To restore the IOS through the console you need:

  • Copy of the IOS file on a PC.
  • Terminal emulation program such as HyperTerminal.

Changing the baud rate from 9600 bps to 115200 bps speeds up the download. To change console speed from rommon:

rommon 1>


Configuration Summary

..<output omitted>..

Console baud: 9600

Boot: the ROM Monitor

Do you wish to change the configuration? y/n [n]:


Enable diagnostic mode y/n [n]:

..<output omitted>..

Change console baud rate? y/n [n]:


Enter rate: 0 = 9600, 1 = 4800, 2 = 1200, 3 = 2400 4 = 19200, 5 = 38400, 6 = 57600, 7 = 115200 [0]:


Note: After changing the console speed and restarting the router in rommon mode, the original terminal session at 9600 bps should be terminated and a new session started to match the 115200 bps console speed.


Use CRC for error checking during the download

Download using Xmodem from rommon >

The xmodem command can be used from the rommon mode to restore the IOS software image from the PC:

Rommon 1>

xmodem -c c2600-is-mz.122-10a.bin

Do not start sending program yet…

Warning: All existing data in bootflash will be lost!

Invoke this application only for disaster recovery.

Do you wish to continue? y/n [n]:


Ready to receive file c2600-is-mz.122-10a.bin . . .

Next, In HyperTerminal select Transfer > Send File.

Specify the image name/location

select Xmodem as the protocol

start the transfer.

During the transfer the Sending File popup will display the status of the transfer.

On completion, return config-register and HyperTerminal settings to normal.

tftp via e0 og environment variabler
TFTP via E0… og Environment Variabler

Downloading af et image med TFTP via rommon er den hurtigste måde at flytte et IOS image til en router. Dette kan gøres ved at sætte environmental variabler og derefter anvende kommandoen tftpdnld:

rommon 1>


rommon 2>


rommon 3>


rommon 4>


rommon 5>


rommon 6>







rommon 7>


..<output omitted>..

Receiving GAD/basic0204/c2600-I-mz.12-1.bin from


File reception completed