1Version 3.1

Module 5Managing Cisco IOS

Software

2Version 3.1

Default sequence for Booting the IOS ImageDo not confuse the IOS image with the IOS configuration that boots from

NVRAM

Flash memory

Tftp Server

ROM (limited image)

Boot System Commands – globally entered and stored in NVRAM in the configuration file

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Locating and Loading the IOS Image

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Boot Options

Remember multiple images can be stored, so specify name

Specify name of image, plus IP address of server

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Boot System Commands

• To find out if there are boot system commands configured on a router, enter any one of the following commands:

– show running-config– show config– show startup-config

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Configuration Register

• The order in which the router looks for system bootstrap information depends on the boot field

• Setting is in the configuration register. The config register number is in NVRAM

• Default is usually 0x2102 or 0x102 for routers with built-in flash• Router command “show version” will tell you what the Hex

number is

Router(config)#config-register 0x101 (to boot from ROM)

Router(config)#config-register 0x102 (or 0x2102 to boot from NVRAM)

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When the router doesn’t boot properly

• Could be:– Config file is missing– Incorrect boot system statement in the

configuration file– Incorrect config-register setting– Flash image itself could be corrupted– Hardware failure

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IOS File System• Routers require both a configuration file and an operating

system file in order to work properly

– The configuration file resides in NVRAM• This startup file is copied into RAM when the router boots• Now the config becomes the “running config”.

– The IOS resides in flash memory

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Backing Up Configuration Files• It is a good idea to use a TFTP server to back up the

configuration files to, and then to copy them back to startup or running configuration.

• To copy to the tftp serverRouter(config)#copy running-config tftp

• To copy from the tftp serverRouter(config)#copy tftp running-config

• Before doing this, you should erase the backup (startup) config in NVRAM and reboot so that there is no configuration in either place.

Router(config)#erase startup-configRouter(config)#reload

• You can also copy and paste the configuration files onto a floppy or other disk so that they will be available.

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Using TFTP to Upload an IOS

Before using TFTP to upload an IOS:• Check memory first (show flash)• Ping the IP address of your TFTP server• Know the name of the file you are copying from, make

sure it is in the default directory

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Backing Up the IOS to a TFTP Server

It is a good idea to back up the current IOS before copying a new one, in case the copy fails - flash is erased BEFORE the actual copy begins.

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Upgrading the IOS from TFTP

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X-MODEM• If the IOS image in flash has been erased or corrupted, the IOS

may need to be restored from the ROM monitor mode (ROMmon). – First, find out why the image didn’t load with:

dir flash: command– If there is an image found, use:

boot flash: (then the name of the image)– If it boots this time, check the config-register value with the show version command first.

– If the register is correct, use show running-config to see if there are boot system commands present.

• If you determine that a new image has to be loaded, you can use the X-Modem method

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X-Modem