FDR (Foreign Device Registration) - Knowledge Base

What FDR Is

Foreign Device Registration (FDR) is a BACnet/IP mechanism that allows a single device on a remote subnet to register with a BBMD and participate in BACnet broadcast traffic — without deploying a full BBMD on the remote subnet.

FDR is commonly used for:

• Remote supervisory workstations accessing a building network over VPN
• A single gateway on an isolated subnet connecting to the main BACnet network
• Temporary diagnostic connections during commissioning

How It Works

1. The foreign device sends a Register-Foreign-Device request to a BBMD, specifying a time-to-live (TTL)
2. The BBMD adds the foreign device to its Foreign Device Table (FDT)
3. The BBMD forwards all broadcast traffic to registered foreign devices
4. The foreign device must re-register before the TTL expires

[!NOTE] FDR requires the foreign device to know the IP address of the target BBMD. Unlike BBMD-to-BBMD peering, FDR is a one-to-one relationship.

FDR vs BBMD

Scenario	Use FDR	Use BBMD
One remote device	✅	Overkill
Multiple devices on remote subnet	❌	✅
Permanent installation	Consider BBMD	✅
Temporary access / diagnostics	✅	❌

Related Pages

• BBMD - Knowledge Base
• BACnet/IP - Knowledge Base
• BACnet Discovery & Network Architecture Reference