Existing BACnet/IP Network

If you have an existing BACnet/IP network that spans IP subnets, chances are that it has at least one existing BBMD. Unless the host for the Niagara station is located on that same IP subnet as an existing BBMD^[3], you must choose one of the following:

Configure As BBMD

Typically this is best if the local subnet is receiving other new BACnet/IP devices, and/or existing BACnet/IP devices on this subnet are not currently supported by a BBMD. You should determine if the IP router for the local subnet supports “directed broadcasting.”

Configure Niagara station as BBMD

Expand the Bacnet network’s BacnetComm container to reveal Network, IpPort, Link, opening the property sheet for the Link component.
In the “Ip Device Type” property, select “Bbmd” from the drop-down list.
To have Niagara read from another BBMD, in the “Bbmd Address” property, enter the address of a known BBMD on a remote subnet, using its full BACnet/IP MAC address, that is IP_Address:UDP_port

For example, for a BBMD at 137.19.61.41 using the standard UDP port 0xBAC0 (decimal 47808), either entry format is accepted: 137:19.61.41:47808 (or) 137.19.61.41:0xBAC0

Figure C.1. BBMD operation configured in BacnetComm, Network, IpPort, Link container
Click Save to enable this configuration. This should update all other BBMDs on the BACnet/IP network with the same BDT information.
Under the Link container, expand the “Broadcast Distribution Table” slot to see child entries. There should be one “localDevice” entry and at least one “BdtEntry” for the remote BBMD entered.
You can also double-click the Broadcast Distribution Table component for its default BDT Manager view. As shown in Figure C.2, the entry for the local device is indicated in a pale blue color.
Figure C.2. Bdt Manager view on BroadcastDistributionTable under Link component of IpPort

This view allows you to manually add new BBMD entries if necessary, or edit or delete existing BBMD entries.
If the router for the local subnet supports “directed broadcasting,” edit the “localDevice” entry’s subnet mask (in decimal) in the “Distribution Mask” field. Otherwise, if the router does not support directed broadcasting, or if you are not sure, leave 255:255:255:255 as the Distribution Mask.
From the Bacnet Device Manager, perform a device discover. If the BBMD configuration was successful, you should see devices from other subnets respond.

Foreign Device Table notes

If the station is configured as a BBMD, in addition to the Broadcast Distribution Table component, the IpPort’s Link container also has a Foreign Device Table component. It accumulates entries for remote BACnet/IP devices that have registered with the station as a foreign device, and includes their registration “time to live” and upcoming purge time.

Double-click the Foreign Device Table component for its Fdt Manager view (Figure C.3).

Figure C.3. Fdt Manager view on Foreign Device Table component under Link component of IpPort

As shown in Figure C.3, this view allows you to manually add new foreign device entries, or edit or delete existing entries. Manually adding entries is not typical, but allows support for devices that cannot register.

If manually adding a device, enter its full BACnet/IP MAC address, that is IP_Address:UDP_port, for example: 137:19.64.29:47808 (or) 137.19.64.29:0xBAC0

The station automatically purges accumulated FDT entries when the requested lifetime expires. However, any manually-added entries are not purged.

Configure As Foreign Device

Typically this is best when a remote subnet BBMD exists and the local subnet has only the Niagara station as a BACnet/IP device, or if other BACnet/IP devices on the local subnet are currently registered as foreign devices.

Configure Niagara station as foreign device

Expand the Bacnet network’s BacnetComm container to reveal Network, IpPort, Link, opening the property sheet for the Link component.
In the “Ip Device Type” property, select “Foreign Device” from the drop-down list.
In the “Bbmd Address” property, enter the address of a known BBMD on a remote subnet. This is the BBMD that the station will attempt to register with as a foreign device.

Enter using its full BACnet/IP MAC address, which means IP_Address:UDP_port

For example, for a BBMD at 137.19.60.176 using the standard UDP port 0xBAC0 (decimal 47808), either entry format is accepted: 137:19.60.176:47808 (or) 137.19.60.176:0xBAC0

Figure C.4. Foreign device operation configured in BacnetComm, Network, IpPort, Link container
In the “Registration Lifetime” property, either accept the default 15 minutes, or enter another value. The station will automatically re-register within this period.
Click Save to enable this configuration. This station attempts to register with the remote BBMD.
From the Bacnet Device Manager, perform a device discover. If the foreign device configuration was successful, you should see devices from other subnets respond.

^[3]If installing the Niagara host on an IP subnet with an existing BBMD for that BACnet/IP network, you are “done”. In the Link property sheet of the Ip Port (BacnetNetwork, BacnetComm, IpPort, Link), leave the “Ip Device Type” property set to “Standard”.