As building automation systems (BAS) have evolved from isolated fieldbus networks to fully IP-connected infrastructures, BACnet/IP has become the dominant communication standard for smart buildings. To keep pace with modern IP architectures — especially the transition from IPv4 to IPv6 — the BACnet community introduced the BACnet Virtual Link Layer (BVLL).
The BVLL acts as a virtual communication bridge that abstracts the details of physical and transport networks (Ethernet, Wi-Fi, VPN, etc.) from the BACnet protocol itself. This abstraction enables seamless interoperability across different types of IP networks and ensures that BACnet can remain future-proof as technologies continue to evolve.
In simple terms, BVLL allows BACnet devices to exchange data over any kind of IP-based transport without worrying about the underlying medium. This design makes BACnet more flexible, scalable, and ready for integration with emerging technologies — from IPv6 to BACnet Secure Connect (BACnet/SC).
If you’re new to BACnet or want to understand its foundational structure, you can first explore our introductory guides:
👉 What is BACnet?
👉 BACnet Protocol Basics
The BACnet Virtual Link Layer (BVLL) is a crucial component in the evolution of BACnet/IP communications. It serves as a logical interface that enables BACnet messages to travel seamlessly over various IP-based networks — including Ethernet, Wi-Fi, VPNs, and even IPv6 infrastructures.
In traditional BACnet systems, messages were tightly bound to the physical network medium. This coupling limited flexibility when integrating devices from different vendors or connecting systems across complex IP infrastructures. The BVLL was designed to remove this limitation by virtualizing the communication layer between the BACnet protocol and the underlying transport mechanisms.
The BVLL sits just below the BACnet Network Layer (BNL) and above the IP transport layers.
It acts as a translator, wrapping BACnet NPDUs (Network Protocol Data Units) into BVLL messages, which are then sent over standard IP packets. This allows BACnet to function independently of the physical transport — ensuring that systems can evolve from IPv4 to IPv6 or to secure connections without changing how BACnet works internally.
“The BACnet Virtual Link Layer represents the essential bridge between the physical network and the logical data exchange — it’s what truly makes BACnet scalable for the IoT era.“
This separation of concerns means that BVLL doesn’t replace the lower network technologies; instead, it harmonizes them. Whether data flows through Ethernet switches, wireless routers, or cloud-based tunnels, BVLL guarantees that every BACnet message is understood and correctly delivered.
This is where the actual BACnet services reside. Devices use these services to read or write data, discover other devices, subscribe to value changes, and more.
| Layer | Description |
|---|---|
| Application Layer | Encodes BACnet objects and services for building automation (e.g., sensors, controllers, schedulers) |
| Network Layer | Handles routing and message forwarding between BACnet devices or subnets |
| Virtual Link Layer (BVLL) | Provides a unified interface between BACnet and IP transport, encapsulating NPDUs into IP packets |
| Transport / Physical Layer | Transmits packets over Ethernet, Wi-Fi, IPv4, IPv6, VPN, or other physical networks |
By abstracting the lower layers, the BVLL ensures that BACnet applications do not need to be redesigned when migrating to new network infrastructures — a key benefit as the building automation industry shifts toward BACnet Secure Connect (BACnet/SC) and cloud-integrated environments.
The BACnet Virtual Link Layer defines several message types that control how BACnet data is transmitted across IP networks.
Each message type serves a specific purpose — for example, forwarding packets between networks, broadcasting to all devices, or returning status information.
These message structures ensure that BACnet communication remains consistent, efficient, and compatible across different IP configurations (local, routed, or tunneled).
| BVLL Message Type | Purpose |
|---|---|
| BVLL-Original-Unicast-NPDU | Transmits a BACnet message directly to a single device on the same subnet. |
| BVLL-Original-Broadcast-NPDU | Broadcasts a message to all BACnet/IP devices on a local network segment. |
| BVLL-Forwarded-NPDU | Transfers a message between different BACnet/IP subnets or routers. |
| BVLL-Result | Returns status or error codes confirming success or reporting transmission failures. |
| BVLL-Register-Foreign-Device | Registers a remote BACnet/IP device (via NAT, VPN, or external network) to a BACnet Broadcast Management Device (BBMD). |
| BVLL-Read-Foreign-Device-Table | Allows a BBMD to share the list of registered external devices with other routers. |
| BVLL-Delete-Foreign-Device-Table-Entry | Removes a remote device registration from a BBMD’s database. |
| BVLL-Distribute-Broadcast-To-Network | Forwards broadcast traffic between BBMDs across multiple BACnet/IP networks. |
In practical terms, these message types make it possible for BACnet/IP systems to operate over distributed and complex network topologies — ensuring that even when devices are separated by routers, VPNs, or cloud networks, the communication remains transparent and reliable.
As the Internet transitions from IPv4 to IPv6, building automation networks must evolve to remain interoperable and secure.
The BACnet Virtual Link Layer (BVLL) plays a central role in this transition — it provides the abstraction and encapsulation mechanisms required for BACnet to operate seamlessly over IPv6 infrastructures.
In traditional BACnet/IP networks, devices used IPv4 addresses for identification and routing. However, IPv4’s address limitations and security weaknesses made it less suitable for large-scale smart building deployments.
By leveraging BVLL, the BACnet protocol can now use IPv6 addressing schemes, which offer:
Because BVLL encapsulates NPDUs independently of the underlying transport, no changes to BACnet applications are required to operate on IPv6 — they automatically benefit from the new addressing and routing capabilities.
The BVLL architecture also laid the foundation for BACnet Secure Connect (BACnet/SC), the latest evolution of the protocol designed for encrypted and authenticated communication.
BACnet/SC replaces UDP transport with WebSocket over TLS (HTTPS), ensuring data confidentiality and integrity over public and private networks.
BVLL’s modular abstraction makes this evolution possible without redesigning the BACnet logic itself. It allows the protocol to adapt to modern IT security standards, VPN topologies, and cloud integration — ensuring that BACnet remains relevant in an era of IoT convergence.
In essence, BVLL is not just a communication layer — it’s a strategic enabler for the next generation of secure, IP-based building automation systems.
By virtualizing the communication between the BACnet stack and the underlying IP infrastructure, BVLL introduces a series of strategic advantages that make building automation networks more interoperable, scalable, and secure.
| Benefit | Description |
|---|---|
| Interoperability | Ensures seamless data exchange across devices using different IP transports (Ethernet, Wi-Fi, VPN, etc.) without compatibility issues. |
| Scalability | Supports large and complex building networks with multiple subnets and thousands of connected BACnet devices. |
| Security | Acts as the foundation for BACnet Secure Connect (BACnet/SC), supporting encrypted, authenticated communications. |
| Future-Proofing | Enables BACnet to evolve with IP technologies — from IPv4 to IPv6 and future transport innovations — without modifying higher protocol layers. |
| Flexibility | Allows the integration of BACnet traffic through VPNs, cloud gateways, or edge infrastructures with minimal configuration changes. |
| Reduced Complexity | Simplifies network configuration by decoupling application-level behavior from physical network constraints. |
| Cost Efficiency | Reduces engineering and maintenance costs by standardizing communication across diverse network types. |
| IoT Integration | Creates a pathway for BACnet to coexist with IoT and IP-based protocols in hybrid or smart-building architectures. |
Thanks to these advantages, the BVLL makes BACnet systems future-ready, enabling building operators and system integrators to migrate toward IPv6 and cloud-native infrastructures without disrupting existing operations.
It’s a key component in the convergence of building automation, IT networks, and the Internet of Things — where Actility’s expertise in secure, large-scale connectivity plays a decisive role.
The BACnet Virtual Link Layer (BVLL) may seem abstract, but its impact is tangible in the operation of modern Building Management Systems (BMS).
It enables BACnet/IP devices — such as HVAC controllers, lighting systems, and smart meters — to communicate reliably across diverse network environments, including Ethernet, Wi-Fi, and cloud-based infrastructures.
Actility plays a key role in this evolution by providing secure IoT connectivity solutions that extend the capabilities of BACnet networks.
Through its ThingPark® platform, Actility enables seamless communication between BACnet/IP devices and LoRaWAN® sensors, creating a unified data layer that bridges field equipment with enterprise IT systems.
In practice, BVLL and Actility’s IP bridging solutions make it possible to connect low-power wireless devices (via LoRaWAN) to high-level BMS protocols like BACnet/IP — ensuring full interoperability from the edge to the cloud.
By combining BVLL’s abstraction with Actility’s expertise in large-scale IoT deployment, building operators gain access to truly hybrid infrastructures, where wired, wireless, and cloud devices all communicate as one ecosystem.
The BVLL provides a virtual communication interface between BACnet and IP networks. It encapsulates BACnet messages into IP packets, enabling devices to exchange data over Ethernet, Wi-Fi, or VPNs without worrying about the underlying transport.
The Network Layer handles routing and message forwarding between devices, while the BVLL deals with how those messages are actually transmitted over IP. In short, the Network Layer decides where messages go; BVLL defines how they travel over the IP medium.
Yes. BVLL supports both IPv4 and IPv6 by design.
Because it abstracts the transport layer, BACnet applications don’t need to change when migrating from IPv4 to IPv6 — they automatically benefit from extended address space and improved network efficiency.
Absolutely. One of BVLL’s strengths is its ability to transmit BACnet/IP messages through VPNs, firewalls, and cloud-based networks using encapsulation.
This makes it ideal for connecting remote sites or multi-campus infrastructures securely over the Internet.
BVLL is part of the traditional BACnet/IP model, using UDP/IP as its transport.
BACnet/SC, on the other hand, is a newer evolution that uses WebSockets over TLS (HTTPS) to ensure encrypted, authenticated communication.
BVLL paved the way for this transition by modularizing the network abstraction.
BVLL standardizes how BACnet messages are encapsulated, ensuring vendor-neutral communication across any IP-based network.
This guarantees that devices from different manufacturers can exchange data reliably, as long as they adhere to BACnet/IP standards.
In IoT-enabled environments, devices communicate over various media — wired, wireless, and cloud.
BVLL ensures that all these elements can speak a common language at the network level, supporting integration with edge gateways, cloud analytics, and LoRaWAN® IoT platforms like Actility’s ThingPark®.
Actility bridges BACnet/IP networks and IoT sensors through secure IP gateways.
By leveraging the BVLL abstraction, Actility enables bidirectional data flow between BACnet devices (e.g., HVAC systems) and low-power LoRaWAN® sensors, offering a unified monitoring and control architecture.
About Actility
Actility, one of the co-inventors of LoRaWAN® technology and a founding member of the LoRa Alliance, is the leader in industrial-grade low-power wide-area network (LPWAN) connectivity and IoT tracking solutions. Actility’s ThingParkâ„¢ platform, which supports multi-radio connectivity (LoRaWAN®, NB-IoT, LTE-M), powers the majority of public networks and numerous private and enterprise networks worldwide. Through its subsidiary Abeeway, Actility offers patented ultra-low power, multi-radio trackers and comprehensive indoor and outdoor geolocation services. Additionally, the ThingPark Market boast the largest catalog of LoRaWAN® devices, gateways, and solutions available.Â
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