HFC Modem Lights Explained

Last Updated: Sunday 14 Sept 2025

There are 2 versions of the Hybrid Fibre Coaxial (HFC) modem, also called an Network Termination Device (NTD).

Check the images below for the version that looks like yours.

New HFC NTD – Arris CM3500



Power	Downstream	Upstream	Online	Meaning
Off	Off	Off	Off	No power to the NBN connection box
On	Flashing	Flashing	Off	Firmware is updating
Flashing	Off	Off	Off	There is a problem with the NBN connection box
On	On	On	On	The NBN connection box is online

Older HFC NTD - Arris CM8200



Power	Downstream	Upstream	Online	Meaning
Off	Off	Off	Off	No power to the NBN connection box
On	Flashing	Flashing	Flashing	Power-on self test
On	Flashing	Off	Off	Downstream search
On	On	Flashing	Off	Downstream found, upstream search
On	On	On	Flashing	Downstream and upstream found - retrieving setup information from NBN
On	On	On	On	Ready for service