1 CCNA 2 v3.1 Module 5. 2 CCNA 2 Module 5 Managing IOS Software.

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CCNA 2 v3.1 Module 5

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CCNA 2

Module 5

Managing IOS Software

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Router Boot Sequence and Verification

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Stages of the router power-on boot sequence

• Cisco Router cannot operation without CISCO Internetwork Operating System (IOS)

• The startup routines must do the following:

Test the router hardware

Find and load the Cisco IOS software

Find and apply configuration statements

Including protocol functions and interface addresses

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The sequence:

Try the interactive media CCNA 2 Module 5 Page 5.1.1

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How a device locates and loads IOS

• Normally the router looks to the NVRAM

• Router can use fallback sequence to load the software

Search for boot system commands in NVRAM

If boot system commands are not found

Search FLASH for IOS

Search for TFTP Server with IOS

Limited IOS from ROM

• Configuration register enable alternatives

Try interactive media lab CCNA 2 Module 5 Page 5.1.2

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Configuration Register

• Saved in NVRAM

• Identify where to boot the IOS image from

• To set the configuration register manuallyRouter#config terminal

Router(config)#boot system flash ios-filename

Router(config)#boot system tftp ios-filename tftp-address

Router(config)#boot system ROM

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To manually boot IOS from Flash

• Advantage of booting from FLASH

Information is not vulnerable to network failures that can occur when loading system images from TFTP servers

• Steps

Router#config terminal

Router(config)#boot sytem flash gsnew-image

Router(config)#Ctrl-Z

Router#copy running-config startup-config

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TFTP Network Server

• Used in case flash memory becomes corrupted

• StepsRouter#config terminal

Router(config)#boot system tftp IOS_image 172.16.13.111

Router(config)#Ctrl-Z

Router#Copy running-config startup-config

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ROM• Used when

Flash memory is corrupted

And Network server fails to load the image

• System image in ROM

Is a subset of the Cisco IOS

Lacks protocols, features and configurations of the full Cisco IOS

• Software may be an older version

• Steps

router#config t

Router(config)#boot system rom

Router(config)#Ctrl-Z

Router#copy run start

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Configuration register

• 16-bit register in NVRAM

The lowest four bits is for the boot field

• To find the current configuration register values

Router#show version

• To change the boot field in configuration register

Use config register command

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• Note When I use nnn it means use the numbers identified when using show version

• To set to ROM monitor mode

Router#config t

Router(config)#config register 0Xnnn0

• Boot from ROM

Router#config t

Router(config)#config register 0Xnnn1

• Examine NVRAM for boot system

Router(config)#config register 0Xnnn2 to F

2 represents boot from FlashTry interactive lab CCNA 2 Module 5 Page 5.1.4

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Troubleshooting IOS boot failure

• What could be wrong if the Router does not boot:

Configuration file has missing or incorrect boot system statement

Incorrect configuration register value

Corrupted flash image

Hardware failure

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How to identify problems

• An incorrect configuration register setting will prevent the IOS from loading from flash

Confirm this using show version

Correct this by changing the configuration register in the configuration and saving this as the start-up configuration

• Corrupted flash image file

Error message

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

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Managing the CISCO File System

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Files in Memory

• Operating system files - IOS…MBs

• Configuration files - …KBs

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• IOS

Stored in Flash memory - non-volatile storage

IOS can be upgraded or have multiple copies

IOS is copied into RAM and run from RAM

• Startup configuration (startup config)

Stored in Non-volatile RAM - NVRAM

Copied into RAM at boot time

• Running Configuration (running config)

Stored in RAM

Used to operate the router

Try interactive lab CCNA 2 Module 5 Page 5.2.1

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IOS naming conventions

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• First part identifies the hardware platform

• Second part identifies the features the file contains

Basic – A basic feature set for the hardware platform, e.g.IP

Plus – Basic features ..IP/FW Plus, and Enterprise Plus

Encryption –

k8 > Less than or equal to 64-bit encryption in IOS version 12.2 and up

k9 > Greater than 64-bit encryption (on 12.2 and up)

• Third part indicates the file format

Is the IOS is stored in flash in a compressed format or not

Is the IOS relocatable(can be copied into RAM) or not(run from flash)

• Fourth part identifies the release of the IOSTry interactive media lab CCNA 2 Module 5 Page 5.2.2

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Managing configuration files using TFTP

• Your configuration file should be backed up on a TFTP server.

Router#copy running-config tftp

Enter the IP address of the TFTP server

Enter the configuration file name or press enter to accept the default name

Confirm the choices by typing yes each time

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• Retrieving or using TFTP config backup:

Router#copy tftp running-config

Select a host or network configuration file

Enter the IP address of the TFTP server

Enter configuration file name or press enter to accept the default name

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Managing configuration files using copy and paste

• Another way to create a backup of the configuration

Capture the output of show running-config

• Select the output in the HyperTerminal screen and paste it into a text file.

• Things that have to be deleted:

show running-config

Building configuration...

Current configuration:

- More -

Any lines that appear after the word "End"

• Add comments

Use an exclamation mark (!) at the beginning of the line

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• Note at the end of each of the interface

Add the no shutdown command

• HyperTerminal can be used to restore a configuration.

Erase the startup configuration file

Router#erase startup-config

Restart the router

Router#reload

Enter router global configuration mode

Router#config t

Transfer the configuration data

From HyperTerminal, click on Transfer > Send Text File.

Select the name of the file for the saved backup configuration

Observe any errors

Return to privilaged mode

Ctrl-Z

Save running configuration files to backup configuration

Router#copy running-config startup-config

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Managing IOS images using Xmodem

• If IOS image in flash is erased or corrupted

Restore IOS from the ROM monitor mode (ROMmon)

Reasons are a corrupt or missing image

• Examine flash with the dir flash: command

• If an image is located that appears to be valid, an attempt should be made to boot from that image.

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• rommon 1>boot flash:c2600-is-mz.121-5

• Why would it boot correctly from ROM not flash?

show version

checks the configuration register to ensure that it is configured for the default boot sequence

If configuration register is correct

show startup-config

See if there is a boot system command instructing the router to use the IOS for ROM monitor

• If router will not properly boot from the image or there is no IOS image

Download a new IOS using

Xmodem to restore the image through the console

or TFTP from the ROMmon mode

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Download using XModem from ROMmon

• To restore the IOS through the console

PC needs a copy of the IOS file to restore and a terminal emulation program (HyperTerminal)

• The IOS can be restored using

default console speed of 9600 bps

baud rate can be changed to 115200 bps to speed up the download

• Use Xmodem in ROMmon to restore IOS software image from the PC

Format xmodem -c image_file_name

E.g., xmodem -c c2600-is-mz.122-10a.bin 

• -c instructs Xmodem to use Cyclic Redundancy Check (CRC) for error checking during the download

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Environment variables

• Fasted way to download IOS image

using TFTP from ROMmon

• ROMmon has very limited functions

No configuration file loaded during boot

• Set environmental variables (set)

IP_ADDRESS – The IP address on the LAN interface

IP_SUBNET_MASK – The subnet mask for the LAN interface

DEFAULT_GATEWAY – Default gateway for the LAN interface

TFTP_SERVER – The IP address of the TFTP server

TFTP_FILE – The IOS filename on the server

• Use the tftpdnld command

When new image is written to flash restart router using i

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File system verification

Router#show version checks

• The current image

• The total amount of flash.

• The source of the IOS image the router used to boot and displays the configuration register

• Configuration register

Determines where the router is to load the IOS from

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Router#show flash command identifies

• IOS image(s) in flash

• The amount of flash memory

• Used to confirm that there is ample space to store a new IOS image