Overview of Upgrading the Controller Software
This section describes the upgrade process and the methods to upgrade the Cisco Catalyst 9800 Series Wireless Controller Software.
Newer versions of the controller software are released at regular intervals. This includes major releases as well as rebuild releases that focuses on bug fixes. Every major Cisco IOS XE software release contains new sets of features that are essential for the enterprise-class customers. Based on your requirement, such as upgrading the full image or applying a software patch for bugs, you can go for an appropriate software upgrade, using either GUI or CLI.
Software Upgrade Options
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Software Maintenance Upgrade: This method installs a software package on the system to provide a patch fix or a security resolution to a released image. This upgrade package is provided on a per release and per component basis, and is specific to the platform.
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Hitless Upgrade: This method allows the APs to be upgraded in a staggered manner, while still being connected to the same controller. This avoids upgrade downtime even for N+1 networks.
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In-Service Software Upgrade: This method upgrades a wireless controller image to a later release or downgrades it to an earlier release while the network forwards packets. As of now, this feature is in beta test program and is supported only within and between major releases.

Note
We recommend In-Service Software Upgrade if you are upgrading the entire image or cold controller SMU. Use Software Maintenance Upgrade for regular upgrades.
The software upgrade time is estimated to be less than 6 hours for a large network. However, the upgrade time depends on factors such as the number of APs, the controller type (9800-80, 9800-L, and so on), and the connectivity between the controller and the APs.
Device Upgrade Options
Device upgrade options are listed below:
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NBAR Dynamic Protocol Pack Upgrade: Protocol packs are software packages that update the Network-Based Application Recognition (NBAR) engine protocol support on a device without replacing the Cisco software on the device. A protocol pack contains information on applications that are officially supported by NBAR, and are compiled and packed together.
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Field Programmables Upgrade: These are hardware programmable packages released by Cisco to upgrade the hardware programmable firmware. Hardware programmable package upgrade is necessary only when a system message indicates that one of the field programmable devices needs an upgrade or when a Cisco technical support representative suggests an upgrade.
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