What is BACnet / IP / MS/TP?

This project is a router: it forwards BACnet network-layer messages (NPDUs) between two different networks — one on Ethernet/UDP (BACnet/IP), one on a serial RS-485 trunk (MS/TP).

BACnet in one paragraph

BACnet is a building-automation protocol. Devices expose objects (sensors, setpoints, binary points). Controllers and tools discover each other and read or write properties. A router does not need a full object database of its own; it moves packets between networks so a tool on IP can talk to a device on MS/TP (and the other way around).

BACnet/IP

  • Runs over UDP (commonly port 47808).
  • Devices have an IP address; BACnet also encodes IP+port as a six-byte “MAC” on the wire for routing.
  • Easy to lab with normal Ethernet; careful with broadcasts and who binds the UDP port (two stacks on the same host/IP often steal each other’s packets).

MS/TP (Master-Slave/Token-Passing)

  • Runs on RS-485: a shared two-wire (plus reference) bus.
  • Masters pass a token; only the station holding the token may initiate requests. Timing is tight — milliseconds matter.
  • Each station has an 8-bit MAC (0–127). Max_Master and baud must match the trunk you join.
  • USB RS-485 adapters show up as Linux serial ports. Always use stable /dev/serial/by-id/... paths, never a bare ttyUSB0 in config.

What this appliance does 

BACnet/IP network  ←→  DIY BACnet Router  ←→  MS/TP network
   (UDP / Ethernet)         (Buildroot OS)         (USB RS-485)

It uses the pinned rusty-bacnet stack for transport and routing logic, wrapped by this repo’s adapter and routerd management plane.

Who does what? See Stack map — rusty-bacnet, bacpypes3, web UI (bacpypes3 is a lab client only; React/routerd are this appliance, not the upstream stack).

Default config keeps forwarding disabled. Lab unlock flags (such as --route-enable) are for controlled benches — not for a random production trunk without a plan.