Fully Unreachable Devices

Overview:

The "Fully Unreachable Devices" diagnostic fails when one or more BACnet devices on the Operational Technology (OT) network do not respond to any of the Who-Is requests sent to them by querying devices for the duration of the capture.

Causes:

• Power Failure: The fully unreachable device may be powered off or disconnected from a power source, rendering it inactive and unable to communicate.
  
• Network Disconnect: The fully unreachable device may not be physically connected to the network, preventing any data transmission.
  
• Physical Disconnection: The fully unreachable device's cabling or connection might have been damaged or disconnected, leading to network isolation.
  
• Programming Errors: The querying device is erroneously searching for a device that is no longer (or never was) connected to the OT network.
  
• Configuration Errors: Incorrect OT network settings, IP address conflicts, or subnet mismatches could prevent devices from communicating properly.
  
• Device Failure: A hardware or software malfunction in the fully unreachable device may result in it being unresponsive to OT network requests.
  
• Network Issues: Network infrastructure problems such as switch failures, cabling issues, or network segment failures may cause devices to be unreachable.
  
• Firewall or Security Settings: Overly restrictive firewall settings or security measures may block the fully unreachable device's communication attempts.
  
• Routing Problems: Incorrect routing configurations or network segmentation issues can isolate fully unreachable devices from the rest of the network.

Implications:

• Incorrect behavior of querying device: The program, sequence or actions of the querying device may be incorrect if it relies on information from the unreachable device.
• Excessive broadcast traffic: In many cases, querying devices may look for the unreachable device every few seconds. If the unreachable device is indeed not necessary, the Who-Is broadcast packets are introducing unnecessary traffic on the overall network which can contribute to network performance degradation and system instability

How to fix it

• Power and Connection: Check power sources and physical connections to ensure devices are powered and connected correctly.
  
• Configuration Review: Review device and network configurations for errors or mismatches and correct them as needed.
  
• Reset Querying Device: Resetting the querying device will clear its cache and force it to reestablish connections with other BACnet devices on the OT network.
  
• Verify Querying Device Programming: If the fully unreachable device is known to no longer be on the OT network, ensure the querying device programming is not still searching for it. If it is, modify the programming as necessary and reset the querying device’s cache to reestablish its connections.
  
• Hardware Inspection: Inspect fully unreachable devices for hardware issues, such as damaged cables or components.
  
• Network Diagnosis: Diagnose network infrastructure to identify and rectify problems affecting device communication.
  
• Device Health Check: Determine if devices are functioning correctly and address any hardware or software malfunctions.
  
• Security Settings: Adjust firewall and security settings to permit necessary communication for BACnet devices.
  
• Network Topology Analysis: Analyze network topology to ensure devices are in the correct segments and routing is configured properly.