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Introduction to Cisco IOS Software

Chapter Description

This sample chapter introduces the fundamentals of Cisco IOS software, the operating system that runs on Cisco routers and switches.

Reloading and Upgrading

A system restart on Cisco routers is called a reload. If the router needs to be reloaded for any reason, the reload command needs to be entered from privileged mode, as shown in Example 4-4. The reload command also allows a time to be set so that the system restarts after the specified time expires.

Example 4-4 System Reload Options

IOS# reload ?
 LINE  Reason for reload
 at   Reload at a specific time/date
 cancel Cancel pending reload
 in   Reload after a time interval
<cr>

The system can also be reloaded by switching it off and then back on again.

The configuration register is used to specify the router's behavior during the reloading process. It determines whether the IOS image should be loaded, determines whether terminal access parameters are provided, and enables or disables the Esc key. The configuration register can be modified in configuration mode using the config-register command.

CAUTION

Use the config-register command only if you completely understand its effects. Incorrect use of this command can make the system inaccessible.

By default, the router first tries to boot from the first image in the onboard system Flash, if available, and then it tries the PCMCIA Flash cards. The user may also specify which images or locations to attempt booting from and the order using the boot system command in configuration mode:

IOS(config)# boot system slot0

This causes the system to attempt booting from an image in the Flash memory in PCMCIA slot 0 before going to the onboard system Flash.

To upgrade the Cisco IOS software version running on a router, you must first determine the right image to upgrade to using the upgrade planners available on http://www.cisco.com.

CAUTION

Attempting to load an incorrect image for your system might leave the system inaccessible. Ensure that you have the correct software image and meet the RAM and Flash memory requirements to run and store the image before installing.

The copy command copies an image into Flash memory. There are many ways to do this, as demonstrated in Example 4-5.

Example 4-5 Options for Copying an IOS Image into Flash Memory

IOS# copy ?
 /erase     Erase destination file system.
 flash:     Copy from flash: file system
 ftp:      Copy from ftp: file system
 null:      Copy from null: file system
 nvram:     Copy from nvram: file system
 pram:      Copy from pram: file system
 rcp:      Copy from rcp: file system
 running-config Copy from current system configuration
 slot0:     Copy from slot0: file system
 slot1:     Copy from slot1: file system
 startup-config Copy from startup configuration
 system:     Copy from system: file system
 tftp:      Copy from tftp: file system
 xmodem:     Copy from xmodem: file system
 ymodem:     Copy from ymodem: file system

The most common methods are TFTP and FTP. After the file has been placed on your TFTP or FTP server, enter the copy command from privileged mode and answer the questions on server IP address and source and destination filenames. After you specify which image the system should load using the boot system command, a reload is required for the new version of IOS to be booted.

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