General procedure for diagnostics and troubleshooting

BACnet on IP involves the use of a large number of components and this results in a certain degree of complexity and a corresponding vulnerability to errors.

If a problem arises in the system, it must be located in a step-by-step procedure. Always start you analysis at the lowest system. Only continue to the next higher system once you are sure that the system is operating correctly. A sketch of the topology is extremely helpful when attempting to locate problems. Create a sketch if none exists.

The following questions can help to troubleshoot communication problems.

Faults

Possible causes & troubleshooting

Is the link signal available on the IP components?

With switches, the link signal is indicated by a continuous or flashing LED. In all devices in the Desigo system, the Service LED is continuously ON if no link signal is detected.

  • Are all connectors firmly in their sockets?
  • Is there supply voltage for the switches?
  • Were the RX and TX connections mixed up on fiber optics?
  • Is the setting for the switch/router port correct?

Are VLAN switches used on the network?

  • Are all BACnet devices configured on the same VLAN?
  • A number of managed switches offer information on their own web interface on connected devices. This includes, for example, port speed, VLAN association, and packet statistics. The latter can also provide references on insufficient cabling.

Diagnostics via wireshark is not possible.

No port mirroring configured on the managed switches

  • Use of hub or configured switch
  • Consultation with customer IT on the use of wireshark

Wireshark does not have the proper BACnet services.

Layer 2 switch is used, but without port mirroring

Use a hub or configure a corresponding layer 2 switch via the web interface

No communication between the BACnet client and the various BACnet devices.

Is a firewall available?

Consultation with IT, cannot be discovered using the diagnostics tool.

Firewall, UDP port configuration is not entered

The BACnet clients cannot access the different BACnet devices on the various VLANs.

BBMD in multiple IP segments

BACnet devices do not have a unique instance number

BACnet devices do not have a fixed IP address (if configured as BBMD)

BBMD used, but all BACnet networks are the same UDP port?

Have you considered notes from technical documentation?

  • Desigo Ethernet, TCP/IP, MS/TP and BACnet fundamentals (CM110666)

Communication, speed on the Desigo network

Compliance with system topology, regarding:

  • Number of devices on a BACnet network.
  • Max. number of 500 commanded group members. No more than 500 addresses can be managed.
  • Max. number of 250 group members. The interface performance when acquiring data is limited, in other words, only a limited number of telegrams can be processes in brief period.