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CCNA Wireless 640-722 Official Cert Guide by David Hucaby

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Maintaining WLC Code Images

Like any other network device, a controller requires a code image to operate. Periodically, you might want to upgrade the code image to a new release so that you can take advantage of bug fixes and new features. Less often, you might have to downgrade the code image to return to a more stable version.

A controller maintains two separate code images—a primary image and a backup image. When a controller boots, it runs the primary image by default. That means you can download a new image file into the backup position on the controller while it is running, with no interruption of service. To run the new image, you must reboot the controller. You can display the two code image versions by navigating to Commands > Config ...

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