A flashing PON light on a MetroFibre ONT means the device is attempting to register on the fibre network but has not completed authentication. If PON continues flashing for more than 5 minutes, it may indicate a line sync issue or access-layer fault requiring escalation.
What the Problem Means
On a MetroFibre ONT, the PON (Passive Optical Network) light indicates whether your device has successfully registered with the fibre exchange.
If the PON light is:
- Solid green → Successfully registered
- Flashing → Attempting to register
- Off + LOS red → No optical signal detected
A continuously flashing PON means the ONT detects optical light but cannot complete network registration.
This differs from a red LOS fault. Flashing PON suggests partial connectivity at the access layer.
Why It Happens
Common causes of flashing PON on MetroFibre:
- Temporary network registration delay
- Authentication sync issue
- Provisioning mismatch
- ONT reboot after power interruption
- Area-level maintenance
Unlike a red LOS condition, flashing PON typically means the optical signal is present, but full line sync is incomplete.
If PON does not turn solid within 5 minutes after boot, further diagnostics are required.
MetroFibre ONT Light Meaning Table
| Light | State | Meaning | Action Required |
|---|---|---|---|
| Power | Off | No power | Check adapter |
| Power | Green | ONT powered | Continue checks |
| PON | Flashing | Attempting registration | Wait 2–5 minutes |
| PON | Solid Green | Registered | Connection active |
| LOS | Red | No optical signal | Escalate signal fault |
| LAN | Green/Flashing | Router connected | Not fibre fault |
If PON flashes indefinitely but LOS is off, signal is present but registration is failing.
Step-by-Step Fix
Confirm Stable Power
- Ensure ONT power source is stable.
- After loadshedding, allow full boot cycle.
Wait Full Sync Window
- MetroFibre registration may take up to 5 minutes after restart.
Properly Restart the ONT
- Switch OFF.
- Wait 2 minutes.
- Switch ON.
- Allow 5 minutes.
Check LOS Status
- If LOS is red → optical signal fault.
- If LOS is off and PON still flashing → registration issue.
Confirm No Area Outage
- Ask nearby MetroFibre users.
If flashing persists beyond restart cycle, escalation may be required for authentication verification or access-layer inspection.
Definition: PON and Line Sync
Confirms successful communication between the ONT and the fibre exchange.
The process where the ONT authenticates and registers on the access network.
If PON flashes continuously, registration is incomplete even though optical light may be present.
When to Escalate
Escalate when:
- PON flashes longer than 10 minutes after restart
- LOS is not red but connection never establishes
- Router shows no internet access
- Neighbours report similar issue
MetroFibre access-layer faults typically resolve within:
- 24–48 hours for sync or provisioning issues
- Up to 72 hours if physical inspection is required
The ISP can verify authentication status, but physical fibre repair requires FNO intervention.
Responsibility Breakdown
| Layer | Responsible Party |
|---|---|
| ONT power & internal setup | User |
| Provisioning & authentication | ISP |
| Fibre access infrastructure | MetroFibre (FNO) |
This prevents unnecessary router resets or WiFi troubleshooting when the issue is at the access layer.
When This Is NOT a PON Registration Issue
If all of the following are true:
- PON is solid green
- LOS is off
- Internet connects but is slow or unstable
Then the issue is not line sync.
See our fibre speed & performance guides