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  • Overview of Fibre Troubleshooting

Overview of Fibre Troubleshooting

3 min read

A collection of things you can do to check your fibre line health. It’s best to do these in the order below.

1. Reboot and stable power #

Reboot your fibre box, router and WiFi access point(s) and make sure they have stable power.

2. Confirm the status lights on your fibre box are normal #

Make sure your fibre box shows that you have a connection with the upstream network. Check the LAN light, if you don’t have any legacy 100Mbps devices make sure that everything is connecting at Gigabit speed. See Lights on your Fibre Box.

3. Check for low signal on the fibre line #

Atomic will have to do this step for you by checking the fibre network portals. You’ll have to open a support ticket. See How to Report a Problem.

4. Basic speed testing #

Do a basic web browser based speed test when connected directly to the fibre ONT/CPE (skip the router and wifi). See Gigabit Speed Tests.

5. Basic ping test for packet loss #

Ping the gateway IP while connected directly to the fibre ONT/CPE. Usually about 1,000 pings are enough. There should be no packet loss. See Troubleshooting with Ping.

6. Large ping test to check MTU #

Ping the gateway IP while connected directly to the fibre ONT/CPE. Send large ping packets and set the ‘don’t fragment’ bit. See Troubleshooting with Ping.

7. Traceroute and MTR tests #

These tests are useful if you know the IP address of a site or service which has slow speeds or packet loss. See Troubleshooting with MTR and Pingplotter.

8. iPerf tests for packet loss under load #

This is the gold standard for testing your line health. You can also use iPerf to check TCP speeds. We have iPerf servers in Cape Town, Joburg and London. See Test your Fibre Line Health with iPerf.

9. Smokeping monitoring for intermittent problems #

If problems are intermittent and you need to monitor a fibre line over a few hours, days or weeks. We can set this up from our monitoring server if you open a support ticket. See How to Report a Problem.

10. TCP stack tuning #

Mostly for Linux users who have fast lines, but can also help with troubleshooting international speed issues. See Test your Fibre Line Health with iPerf.

Edge Cases and Intermittent Problems #

Troubleshooting intermittent problems can be tricky. Here are a few things to check:
  • Stable power – is your router rebooting? Check your power plugs and ideally get a DC-UPS.
  • Is your DC-UPS old or too small?
  • Temperature – make sure your router and fibre box / ONT are in a well-ventilated area.
  • Check all your cabling and connectors. Make sure your fibre patch lead is not curled too tightly.
  • Has anything changed on your network recently? Cabling, cleaning, new network devices?
  • If you have an ONT/CPE with more than one Ethernet port, make sure you are connecting to the port with an active service.
  • Check the DNS settings on your router and your devices. Try 9.9.9.9 as DNS server.
  • Are you using a VPN service?
  • Check that there is only one DHCP server on your local network.
  • Are you using all your upstream bandwidth? Check file syncing service are not doing big uploads.
  • Test from more than one PC / laptop / phone and see if you can reproduce the problem.
  • Make notes of when you notice the problem happening and see if you can spot a pattern.

Updated on 15 April 2025
Scope of Services
Table of Contents
  • 1. Reboot and stable power
  • 2. Confirm the status lights on your fibre box are normal
  • 3. Check for low signal on the fibre line
  • 4. Basic speed testing
  • 5. Basic ping test for packet loss
  • 6. Large ping test to check MTU
  • 7. Traceroute and MTR tests
  • 8. iPerf tests for packet loss under load
  • 9. Smokeping monitoring for intermittent problems
  • 10. TCP stack tuning
  • Edge Cases and Intermittent Problems

About Atomic

Atomic is a Specialist Fibre ISP in Cape Town and the Cape Winelands. Our narrow focus makes us #1 in Google and Hellopeter ratings!

We are Fiercely Independent, Founder-Run and Fibre-Only. Big enough to be Reliable, small enough to be Agile and Friendly. We are Gamer & Techie friendly.

Read our Epic Reviews and Switch to Atomic today!

🏆 Reviews: Google & Hellopeter

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