NBN FTTP Connection Box Status Lights

Key Takeaways

Optical is the light that matters. Solid green means the fibre is up. Slow flashing green is normal traffic. Red means the link to the network is down, and no amount of rebooting your router will fix that.
Power off means everything off. Every other light goes dark with it. Check the PSU before you diagnose anything else — it’s a separate brick from the connection box.
Alarm red is not yours to fix. It’s a fault on the connection box itself. That’s an nbn field call via your retail provider, not a home troubleshooting step.
Only one Port light will normally be lit. Your service is provisioned against a specific UNI-D port — usually port 1. A dark port isn’t a fault if nothing’s plugged into it.
The lights can be switched off. There’s a physical button for it, and it doesn’t affect the service. Useful when the box lives in a bedroom.

The nbn connection box — the Network Termination Device, or NTD — is the demarcation point in an FTTP install. Fibre in one side, ethernet out the other, and a row of indicator lights that tell you which side of that boundary a problem sits on.

That last part is the useful bit. When something breaks at 11pm, the lights answer one question before you touch anything: is this the carrier’s problem or mine? Getting that right saves you an hour of rebooting equipment that was never at fault.

This covers the four-port FTTP connection box, which is the common residential unit. There’s a newer single-port variant with a reduced light set; the logic is the same, there’s just less of it.

What the lights mean

The four-port box has seven indicators. Straight from nbn’s own documentation for the unit:

Light	State	Meaning
Power	Off	No power reaching the box. Every other light will be off too.
	Slow flashing green	Starting up.
	Fast flashing green	Receiving a firmware update. Leave it alone.
	Solid green	Normal.
Optical	Off	Not connected to the nbn network.
	Solid green	Connected and ready to pass data.
	Slow flashing green	Data moving across the fibre. Normal in use.
	Red	Lost the connection to the network.
Alarm	Off	Normal. Off is the good state here.
Alarm	Red	Fault on the connection box.
Port 1–4	Off	No service on that port, or nothing plugged in.
	Solid green	Active service, no traffic right now.
	Fast flashing green	Active service passing traffic.

Worth noting the naming mismatch: nbn’s consumer documentation calls them Port 1 to 4, while provisioning systems, RSP support staff and the industry generally call them UNI-D 1 to UNI-D 4 — User Network Interface, Data. Same four sockets. If someone on the phone asks which UNI-D you’re plugged into, they mean the numbered ethernet ports.

Reading it as a fault tree

Work top down. The lights are ordered by dependency, and there’s no point looking at a lower one until the one above it is healthy.

Power off. Nothing else means anything. The FTTP install has a separate power supply unit, and it’s a distinct box from the NTD — check that it’s powered and that the lead between the two is seated. Older installs shipped a PSU with a backup battery compartment, which is the usual culprit on units of that vintage.

Optical red or off. The fibre path is down. This is upstream of you and there is nothing at your end that fixes it — power-cycling the NTD, swapping ethernet cables and factory-resetting your router are all wasted effort. Off generally points at a provisioning or fibre-path problem; red means it had a link and lost it. Either way it’s a call to your retail provider, who raises it with nbn.

Alarm red. Hardware fault on the box. Again, a provider call — the NTD is nbn’s equipment and you’re not meant to service it.

Power and Optical solid green, Port light dark. Now it’s your side of the demarc, and this is the most common genuine home-network fault. The fibre is fine and the box is healthy. Check that your router is plugged into the port your service is actually provisioned on. Only one UNI-D is active for a standard single service, and it’s usually port 1 — but not always, and there’s no way to tell by looking. If you don’t know which, your provider does.

Everything green, no internet. The physical layer is done and the problem is above it — PPPoE credentials, VLAN tagging, DHCP, or your router. The NTD has told you everything it can at this point.

The lights button

There’s a LIGHTS ON/OFF button on the unit. Pressing it turns the indicators off without touching the service — it’s purely cosmetic, and it exists because these boxes are frequently installed in bedrooms and hallways.

The obvious trap: if someone has pressed it, a working box looks like a dead one. Before diagnosing a completely dark NTD, press the button once and see if the lights come back.

Finding the serial number

Providers ask for the NTD serial number when placing or troubleshooting an order. It’s on a barcode label on the unit itself, alongside the model number. On boxes fitted with the plastic cover — standard on installs from around mid-2013 — you’ll need to unclip the cover at the bottom and lift it away to see the label.

Take a photo of it while you’re there. It’s easier than getting behind the thing twice.

What the lights won’t tell you

The NTD reports on the fibre path and the physical ethernet handoff. It has no visibility above that, which means a fully green box is entirely consistent with:

Wrong or expired PPPoE credentials on your router
An outage in your provider’s network rather than nbn’s
DNS failures — everything routes, nothing resolves
Your own Wi-Fi being the actual problem

All green means the carrier has delivered a working service to your wall. Past that point it’s yours.

Sources

nbn — Fibre to the Premises four port connection box, the light-state definitions above
nbn — Fibre to the Premises one port connection box, the newer reduced-light variant
nbn — Understanding your connection box