RDMnet

showstack / protocols / rdmnet

Also called E1.33, RDM over IP.

Carries RDM messages over IP, with brokers routing between controllers and devices instead of every controller polling every wire. It also defines LLRP, a multicast side channel for finding and fixing devices whose IP settings are wrong.

Device managementOpenESTAReported

Stewarded by ESTA (Entertainment Services and Technology Association).

Management Housekeeping, no deadline

Discovery, monitoring, configuration, backups, updates. Useful, and none of it has a deadline of its own.

What kills it. Nothing kills it. That is the problem: with no deadline it has no manners, and it will happily starve everything that does have one. Putting it on a show VLAN is the commonest self-inflicted wound in the industry.

Why this one, and not what the category suggests. The same job over IP, and the same reasoning.

The four flows, and why the model is worth having →

Ports

udp/5569 LLRP discovery and configuration (multicast)
IANA registers 5569/udp as rdmnet-device and 5569/tcp as rdmnet-ctrl to PLASA for E1.33. Broker connections do not use a fixed port; brokers advertise their listening port over DNS-SD.

Multicast

239.255.250.133 (LLRP request, IPv4)
239.255.250.134 (LLRP response, IPv4)
ff18::85:0:0:85 (LLRP request, IPv6)
ff18::85:0:0:86 (LLRP response, IPv6)
Multicast is used only by LLRP. Normal RPT traffic between controllers, brokers and devices is unicast TCP through a broker. Addresses as defined in the ETC reference implementation of E1.33.

What goes wrong

Nothing works without a broker. With no broker running in the scope, controllers and devices sit there discovered and unable to exchange a single message. Some products embed a broker, most do not.

Discovery is DNS-SD, normally over mDNS, which does not cross a subnet boundary without a reflector or a unicast DNS-SD server. That is the usual reason a device on another VLAN never appears in the list.

Scope is a text string and it defaults to "default". A device left on the wrong scope is invisible to the controller even though it is on the right network and answers a ping.

LLRP is the recovery path, not the working path. It is multicast and deliberately limited in what it can do, so never design a routine control workflow around it.

Dynamic UIDs are allocated by the broker in the 8000h-FFFFh manufacturer ID range and are not stable across sessions. Never key a patch, a preset or a show file off one.

A gateway presents its downstream DMX responders as endpoints, but the wire behind it is still RS-485 RDM. A slow or marginal DMX leg gates the whole conversation regardless of how fast the network is.

TCP connections to the broker are health-checked with heartbeats. A network that drops idle flows, or a firewall with a short state timeout, will make devices appear and disappear on a cycle.

What speaks RDMnet (1)

Product	Direction	Notes
Wireshark Wireshark Foundation	in	RDMnet dissector added in Wireshark 3.4.0 (commit 'Added RDMnet protocol', March 2020).

Open source implementations

ETCLabs RDMnet — C, Apache-2.0

Typical use

Configuring RDM devices across a whole building from one controller
Recovering nodes that have the wrong IP address, via LLRP
Gateways exposing their downstream DMX/RDM responders to the network
Multi-controller environments where a single DMX line would be a bottleneck

Sources

ANSI E1.33-2019 (RDMnet), approved 27 August 2019 — free download — ESTA Technical Standards Program primary
ANSI E1.33-2019 preview — scope, Broker/Controller/Device roles, DNS-SD, LLRP — ESTA / ANSI webstore primary
ETCLabs RDMnet — include/rdmnet/defs.h (LLRP addresses, LLRP_PORT, default scope, DNS-SD service type) — Electronic Theatre Controls
IANA Service Name and Transport Protocol Port Number Registry (5569 rdmnet-ctrl / rdmnet-device, PLASA E1.33) — IANA primary

Understand the mechanism

DMX on the wire

Something wrong, or missing?

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