# Interact with local IoT devices
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*Client devices* are local IoT devices that connect to and communicate with a Greengrass core device over MQTT. You can connect client devices to core devices to do the following:
+ Interact with MQTT messages in Greengrass components.
+ Relay messages and data between client devices and AWS IoT Core.
+ Interact with client device shadows in Greengrass components.
+ Sync client devices shadows with AWS IoT Core.
+ Use IPv6 for local messaging.

To connect to a core device, client devices can use *cloud discovery*. Client devices connect to the AWS IoT Greengrass cloud service to retrieve information about core devices to which they can connect. Then, they can connect to a core device to process their messages and sync their data with the AWS IoT Core cloud service.

You can follow a tutorial that walks through how to configure a core device to connect and communicate with an AWS IoT thing. This tutorial also explores how to develop a custom Greengrass component that interacts with client devices. For more information, see [Tutorial: Interact with local IoT devices over MQTT](client-devices-tutorial.md).

**Topics**
+ [AWS-provided client device components](client-device-components.md)
+ [Connect client devices to core devices](connect-client-devices.md)
+ [Relay MQTT messages between client devices and AWS IoT Core](relay-client-device-messages.md)
+ [Interact with client devices in components](interact-with-client-devices-in-components.md)
+ [Interact with and sync client device shadows](work-with-client-device-shadows.md)
+ [Use IPv6 for local messaging](use-ipv6.md)
+ [Troubleshooting client devices](troubleshooting-client-devices.md)