Refer to the exhibit. Based on the MQTT client output, which action should be taken so that the connection to the broker can be established?

Question

Exhibit

Options

• AChange the username/password.
• BOpen port 1883 on the network firewall.
• CChange the IP address of the broker.
• DAdd the certificate.

• A
  78% (28)
• B
  8% (3)
• C
  11% (4)
• D
  3% (1)

Explanation

Option A is correct because the MQTT client output would display an error such as "Connection Refused: bad username or password" (return code 4 or 5), which directly indicates authentication failure - the broker is reachable but rejecting the credentials. Option B is wrong because if port 1883 were blocked, the error would be a connection timeout or refused at the TCP level, not an MQTT-level authentication error. Option C is wrong because the client successfully reached the broker (an MQTT response was received), proving the IP address is valid. Option D is wrong because TLS certificate errors produce a distinct handshake failure message, not a credential rejection.

Memory tip: Match the error to the layer - MQTT auth errors (bad username/password) live at the application layer, while port blocks live at the network layer and certificate issues at the transport layer. If the broker responds at all, the network path is fine.

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