The nRF5 SDK for Thread and Zigbee includes the following examples that demonstrate the OTA Upgrade process:

Zigbee OTA Upgrade Client Example demonstrates a Zigbee OTA client device; it serves as a guide on how to add a OTA function to your own device.
Zigbee OTA Upgrade Server Example with image transfer over BLE demonstrates a Zigbee OTA server device; it can be used to propagate OTA images inside the Zigbee network.

Warning

The OTA Upgrade from nRF5 SDK for Thread and Zigbee v3.0.0 to any more recent version of the SDK must be done with caution due to a risk of NVRAM corruption. The NVRAM corruption can take place if the relation between the number of source/destination binding table entries equals:

for end devices: src = 37 - 2 * dst
for routers/coordinator: src = 73 - 2 * dst

In case of the NVRAM corruption, the device requires a factory reset and recommissioning on the network.

Note: The pre-3.1.0 versions of SDK used an unofficial OUI. This OUI should not have been used in end products. This means that an example built with the current version of the SDK will render a device with a different EUI64 than an example built with the previous version of the SDK. In case of an OTA upgrade, this might require a factory reset and recommissioning of the device.