Art-Net and sACN troubleshooting: a symptom-based checklist

This is the checklist to work through when Art-Net or sACN misbehaves: no output, nodes that cannot be discovered, flickering fixtures, or stuttering fades. Each section starts from a symptom; the checks are ordered to catch the most common faults first.

First: isolate the problem

• Bench test the smallest chain. One computer, one node, one fixture, a single Ethernet cable from computer to node (no switch, no Wi-Fi). If that works, reintroduce switches one at a time until the fault returns; the last piece added is where the problem lies.
• Read the node's port activity LED. Most nodes blink or change colour when valid data for a patched universe arrives. LED shows traffic but the fixture is dark: the fault is on the DMX side (address, cable, termination; see DMX signal loss). LED shows nothing: the fault is on the network side.
• Run only one lighting application at a time. Multiple applications on one computer (EMU, ELM, Pro Utility, or third-party software) can compete for the network port and cause output errors. Close all but one, then rescan.

No output at all

1. Subnet mismatch. Sender and node must be in the same IP range with the same subnet mask. ENTTEC's current nodes default to DHCP and fall back to 192.168.0.10 (mask 255.255.255.0) when no DHCP server answers, the usual case on a direct cable to a laptop. Some third-party nodes default to the Art-Net 2.x.x.x convention (mask 255.0.0.0) instead. Mixing schemes never works, even though discovery may still find the node, and mismatched netmasks silently break directed broadcast too. Match your computer to the node: guides for Windows and macOS.
2. Universe off-by-one. Art-Net counts universes from 0; sACN and much lighting software count from 1, so one tool's "universe 1" can be universe 0 on the wire. Trying the adjacent universe number is a legitimate diagnostic. Art-Net also splits its address into Net, Sub-Net and Universe fields; both ends must agree on all three, and the node's configuration page shows the raw values.
3. Firewall. Art-Net uses UDP port 6454, sACN uses UDP port 5568, and desktop firewalls routinely drop both. Allow the application through or open the port; disabling the firewall briefly confirms the diagnosis.
4. Wrong network adapter. Laptops with Wi-Fi plus Ethernet often send data out the wrong interface. Select the correct adapter in the software, or disable Wi-Fi while testing.
5. Port direction and protocol. A bidirectional port set to input never outputs, and a port set to sACN ignores Art-Net (and vice versa).
6. Duplicate or stale IPs. Nodes fresh from the box can share a default address; connect and readdress one at a time. On unicast rigs, a node that changed address stays dark until the controller's patch is updated.

Software cannot discover the node

• Art-Net discovery (ArtPoll) is broadcast: it does not cross routers, so computer and node must be on the same local network.
• Broadcast storm control on managed switches (for example the Netgear M4300) stops forwarding broadcast traffic above a set threshold, silently dropping the ArtPoll packets discovery depends on, and can add latency. Disable it, or raise the threshold, on lighting ports.
• On macOS, the system firewall can block the broadcast UDP packets ArtPoll relies on; turn it off to test.
• Discovery working while output fails usually means a subnet mismatch (item 1 above), not a discovery problem.

sACN specific: multicast and IGMP

sACN sends each universe to its own multicast group. On unmanaged switches multicast floods every port, which works but does not scale. On managed switches, misconfiguration has distinctive signatures:

• Nodes never receive data: IGMP snooping enabled but no IGMP querier, so group memberships are never learned.
• Output stops minutes after load-in: the querier fails to refresh memberships and subscriptions time out.
• Low packet rates: storm protection triggering on misconfigured multicast.

Details in sACN Multicasting and IGMP. Capture caveat: Wireshark on a separate machine cannot see multicast or IGMP traffic unless it subscribes to the group, so an empty capture proves nothing.

Flickering, or fixtures fighting

Flicker on an otherwise healthy network almost always means two sources on the same universe. Check whether merging is enabled on the node, whether more than two sources exist (ENTTEC nodes merge a maximum of two), and whether both streams come from the same IP address, which also breaks merging. Under HTP merging, a source holding a channel at 50% stops another source fading below it; zero unwanted sources to release control (see Output Merging). On sACN, deliberate multi-source rigs should use per-universe priority (1 to 200, default 100) instead: see sACN priority handover.

Stuttering fades and dropped frames

Overload shows up as jerky fades, stepped movement, fixtures freezing on the last value, and faults that appear only under full-rig output. In order of likelihood:

• The controller is still in broadcast mode on too large a rig; every node then inspects every universe, and small node CPUs hit their ceiling first. Switch to unicast: see Art-Net network design.
• 100 Mbit ports or links in the path, where broadcast floods bite first.
• Congested uplinks between chained switches.
• Wi-Fi anywhere in the signal path; not recommended for show-critical output (see Sending over WiFi).
• Genuine bandwidth shortfall: budget roughly 0.31 Mbit/s per Art-Net universe and 0.39 Mbit/s per sACN universe at 60 FPS, per Bandwidth Planning.

Web interface loads, but fields do not populate

The usual causes are browser cache and security software. Real-time internet scanning in endpoint protection such as Sophos can block the page's data requests, leaving fields empty or the page half-loaded. Try a hard refresh (Ctrl+Shift+R), another browser, and temporarily pausing the antivirus; on managed networks, confirm the firewall is not filtering these ports:

More in Web interface troubleshooting and Connecting to the Web Interface.

Still stuck?

If you are commissioning rather than fixing, the Art-Net node setup guide builds the chain in a known-good order, and the Art-Net explainer covers addressing in depth. Otherwise contact ENTTEC support with your topology, IP addresses and masks, and both ends' universe configuration; that turns most tickets into a one-reply fix.