Multiple AP Firmware Support in the SZ100/vSZ-E/SCG200-C/SZ300/vSZ-H The AP firmware releases that APs use are configured at the zone level. This means that APs that belong to one zone could use a different AP firmware release from APs that belong to another zone. Attention: SZ300/SZ100/vSZ-E/vSZ-H is referred as controller in this section. Remember: If you have AP zones that are using 3.4.x or 3.5.x and the AP models that belong to these zones support AP firmware 3.6 (and later), change the AP firmware of these zones to 3.6 (or later) to force these APs to upgrade their firmware. After you verify that all the APs have been upgraded to AP firmware 3.6 (or later), proceed with upgrading the controller software to release 5.1. Attention: In earlier releases, Essentials controllers (vSZ-E or SZ100) automatically upgraded both the controller firmware and AP firmware when the system is upgraded. In release 3.5, however, the concept of Multi-Zone was introduced, which slightly changed the upgrade workflow where the system and the AP zones upgraded independently. When upgrading the controller to 5.1, the AP Zone firmware remains the same. Up to Three Previous Major AP Releases Supported Every platform release can support up to three major AP firmware releases, including (1) the latest AP firmware release and (2) two of the most recent major AP firmware releases. This is known as the N-2 (n minus two) firmware policy. Note: A major release version refers to the first two digits of the release number. For example, 3.6.1 and 3.6.2 are considered part of the same major release version, which is 3.6. The following releases can be upgraded to release 5.1: 5.0 3.6 3.6.x The AP firmware releases that the controller will retain depends on the controller release version from which you are upgrading: If you are upgrading the controller from release 5.0, then the AP firmware releases that it will retain after the upgrade will be 5.1 and 5.0. If you are upgrading the controller from release 3.6.2, then the AP firmware releases that it will retain after the upgrade will be 5.1 and 3.6.2 (and 3.6.1 if this controller was previously in release 3.6.1). If you are upgrading the controller from release 3.6.1, then the AP firmware releases that it will retain after the upgrade will be 5.1 and 3.6.1. All other AP firmware releases that were previously available on the controller will be deleted automatically.