Error 66 With MQTT on a Real-Time Controller in LabVIEW

Issue Details

• I am using a Real-Time (RT) controller as an MQTT Publisher or Subscriber, but I keep seeing error 66. How can I fix this?
• My MQTT Publisher or Subscriber does not connect to my Broker because "the network connection was closed by the peer". What's causing this?
• My NI Linux Real-Time controller keeps producing the below error when I attempt to publish an MQTT message.

Solution

This error can occur due to one of the following reasons:

• Incorrect start-up procedure of the Broker and Publisher/Subscriber.
• Communication being blocked by a Firewall.
• Incorrect RT controller settings or configuration.
• Invalid MQTT parameters.

Review the points below to resolve this error:

• Ensure that the MQTT port is open on the Broker PC and that the client can reach it.
  • If the Broker is running on a Windows PC, create a Firewall rule to allow communication on the port.
  • Refer to [External] Create an Inbound Port Rule for instructions.
  • Ping the MQTT port from the client as described in [External] How to Ping Specific Port Number in Linux and Windows.
• Make sure that the Broker is started/created before the Publisher or Subscriber.
• Verify that TCP/IP is enabled on the RT controller.
  1. From the LabVIEW project window, right-click the controller and select Properties.
  2. In the pop-up window, select the VI Server tab.
  3. Ensure that the TCP/IP option is enabled and that Port contains your MQTT port number.

• If using an RT controller with dual Ethernet ports, ensure that the second port (eth1) is on a different subnet than the first port.
  • Refer to Setting Up Dual Ethernet Port Real-Time Controllers for instructions.
• Depending on the MQTT toolkit used, enable or increase the time of the Keep Alive parameter.
• If connection flags have been set, ensure that the required values are being passed into the configuration.
  • For example, if the Username or Password flags are true, a valid username and password must be passed into the MQTT connection function.

Additional Information