MQTT Plug-in

You can configure the following properties in the MQTT plug-in settings.

Legacy / Migration

Up to version 5.4, the MQTT implementation could be selected under Expert settings → Implementation. The following options were available:

• Legacy Automatic
• Legacy Strider MQTT
• Legacy MQTT.NET
• MQTT.NET (recommended)

Starting with version 5.5, a migration notice appears for old configurations, recommending a switch to MQTT .NET V2.

Starting with version 5.6, only MQTT .NET V2 is available.

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Tab: Router Settings

Field	Description
Name	Assign a unique name to the MQTT connection.
Cloud Profile	Select the desired profile: MQTT Standard, AWS, Azure IoT, Wago Cloud.

You can check the current connection by clicking Test Connection.

Cloud Profiles

The cloud profiles extend the standard configuration with additional tabs:

• AWS IoT Cloud
• Azure IoT Hub

tip

For more information on using MQTT and the cloud profiles, see our Knowledge Base:

https://www.opc-router.de/knowledge-base/

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Tab: Connection settings

Connection details

Field	Description
Broker connection	Enter the address of the MQTT broker.
Port	TCP port of the broker (default: 8883).
MQTT version	Select the protocol version (e.g., MQTT v5 or MQTT v3.1.1).
Quality of Service type	Select the default QoS: 0 – at most once, 1 – at least once, or 2 – exactly once.

Performance

For details on latency, network round trips (RTT), and internal synchronization during publish operations, see MQTT Performance.

Authentication

Field	Description
Username	Username for logging in to the broker.
Password	Selection of a secret. Use the buttons to create, edit, or delete a secret.
Client ID	Unique client ID. Supports placeholders: ${hostname} to get the system name, ${hostname:lower} to get the system name in lowercase, #[INSTANCE], #[INSTANCE:<numerischer wert="">], #[RAND:<numerischer wert="">]. This is helpful for connection pooling or project synchronization to automatically generate different IDs per instance. Example: MyInstance-${hostname}-#[RAND:4]
Buttons	Random – generates a random ID. Client ID Template – inserts the default template into the input field.

Enable TLS/SSL

Field	Description
SSL protocol	Selection of supported protocols (e.g., TLSv1.2, TLSv1.3).
Client certificate	Selection of a client certificate (or Without).
Trusted certificates	Specify which certificates are accepted (e.g., All (unsafe), Windows, Router).

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Tab: Storage

Field	Description
Enable MQTT Data Storage	When enabled, the last received MQTT message for each topic is saved to disk. This feature is required to use the MQTT Storage Read Transfer Object.
Pattern	A subscription is created for each added topic pattern. Supports wildcards + and #.
Note	Free text describing the purpose or origin of a topic.

How it works

When the MQTT Data Storage function is enabled, the OPC Router creates automatic subscriptions for all registered topics. The received messages are stored persistently – only the most recent message per topic (older values are overwritten). These stored values can be retrieved specifically using the MQTT Storage Read Transfer Object.

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Tab: First Will

Field	Description
Enable First Will	Enables the sending of a First Will upon connection establishment.
Retain First Will	Broker stores message for later delivery.
Topic	Target topic for the First Will.
Payload	Content of the First Will message.
Quality of Service	Service quality (0, 1, or 2).

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Tab: Last Will

Field	Description
Enable Last Will	Enables sending a message upon connection termination.
Retain Last Will	Broker saves message for later delivery.
Send Last Will on disconnect	Sends Last Will even upon manual disconnection.
Topic	Target topic for the Last Will.
Payload	Content of the Last Will message.
Quality of Service	Service quality (0, 1, or 2).

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Tab: Advanced

Connection Pool

Field	Description
Enable Connection Pooling	When enabled, a single connection is used for subscriptions and multiple connections for publish operations. Useful for high message volumes.
Min. connections	Minimum number of connections.
Max. connections	Maximum number of connections.
Connection idle timeout	Time in minutes after which inactive connections are closed.

Subscription / Trigger

Field	Description
Wait for transfer	The router responds to the broker only after the transfer has completed or failed.
Enable message deduplication	Prevents multiple triggers for identical messages within a time window.
Deduplication Time Window	Time in seconds during which identical messages are ignored.

Session Options

Field	Description
CleanSession	Starts a new session without saved messages (disable for persistent sessions).
Keep alive (s)	Ping interval in seconds.
Timeout (ms)	Wait time in milliseconds for reconnection.