Overview of Fibre Internet Troubleshooting

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. See First Steps to Fix your Fibre.

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 First Steps to Fix your Fibre. If you have a fast line also 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

• 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?
• 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.