Transcript Module 5

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
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Normally the router looks to the NVRAM
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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
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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 manually
Router#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
• Steps
Router#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 Flash
Try interactive lab CCNA 2 Module 5 Page 5.1.4
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Troubleshooting IOS boot failure
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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 IOS
Try 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
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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
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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
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