@maxperhour 

Switch Deco mesh to Access Point mode and you'll find if the issue is software related (Deco configuration settings) or hardware related. In Access Point mode, Deco should pass through all Ethernet traffic.

  @Alexandre. 

So I placed the Decos into AP mode, and while the lights flashed red the app showed them working, in AP mode and could connect fine. Ran a speedtest via ethernet and still the same speed unfortunatly.

maxperhour wrote

  @Alexandre. 

 

So I placed the Decos into AP mode, and while the lights flashed red the app showed them working, in AP mode and could connect fine. Ran a speedtest via ethernet and still the same speed unfortunatly.

  @maxperhour 

That eliminates Deco mesh configuration settings as a cause.

If your Main Deco is connected to the router, its LED light should be either solid Green or solid White (same as in Router mode)  after very brief period while Deco switches between Router and AP mode. 

  @Alexandre. 

I waited around 5 minutes but only had red lights (main deco was solid and other decos flashing). I assumed it was just a bug as I have had issues in the past with these decos displaying a red light while everything was working (which is always fixed with a reboot). Either way it seems that AP mode made no difference to the ethernet speed, so does this mean it is hardware related?

  @maxperhour 

Yes, but "hardware" could mean not just Main Deco but also Ethernet wiring and your ISP router. You said you tested it all, and I have no reasons not to believe you, but still the issue exists.

So, if you want formally correct opinion: what you see is not related to Deco content filtering and bandwidth throttling settings available in Deco mesh Router mode. 

  @Alexandre. 

Well either way that narrows it down so thank you.

I used the same ethernet cable to test the speed from my main Deco and then my modem, and it went from 600Mbps to 900Mbps, so don't believe there is an issue with that cable. I definetly tried switching the cable that connects my main deco to the modem, so it can't be that cable either. I also tried using different ports on both the modem and the Deco. I think that eliminates wiring and ISP router?

  @maxperhour 

To be on the safe side I would also try very short, 3 feet, Ethernet cable with Main Deco. Preferably one you had for a long time and if it is Cat5E - that would be the best option.

In general, this is how I would troubleshoot an issue similar to what you have. I would change Deco mesh to AP mode to eliminate everything configuration related that would impact speedtest results. Then, I would start looking at wiring, Deco hardware, router. Of course, I would expect Deco mesh stay in perfect condition. If you are saying Main Deco LED goes Red occasionally even in Router mode and only recovers after reboot - I would focus on that part. Because, it means Main Deco either loses connection to Internet or fails to perform Internet health check such as DNS name resolution of popular domain names. It could also mean Deco hardware issues, but I don't have enough info to claim that for certain.

Finally, and I hope that does not sound wrong way, are you sure when you run speed tests through Ethernet connection with Deco your computer is actually connected to Deco by Ethernet and not by WiFi?

Because, 600Mbps is quite close to Deco S7 WiFi capabilities. In fact, my first reply was that 600Mbps is what you should expect from Main Deco on WiFi, and then I had to delete and rewrite it when I noticed you are saying speedtest is done through the Ethernet. 

Usually, if speedtest is limited by under 100Mbps, that means Main Deco negotiated 100Mbps Ethernet link speed with the router. Other than that, one should expect close to gigabit speeds through the Ethernet and 600-650Mbps with WiFi. Having 600Mbps on Ethernet with everything tested as you did and found it healthy is quite unusual. I can't explain that, honestly.

  @Alexandre. 

Thanks so much for the detailed troubleshooting steps! I'll run through them step by step when my housemates are next not using the internet.

So currently I've been using a 20m Cat6 cable that goes form the Main Deco to the Deco in my room to test the ethernet connection (ie unplugging from the satelite Deco into my PC then the other end into the modem/another port on the main deco). You are right that I should probably do a test with a shorter cable and a different device, however I don't own anything else with an ethernet port so I'll have to try to find something to test with. I assumed that because I got 900Mbps with that cable and my PC they weren't the issue, but its worth ruling them out for certain.

I did read on the forum earlier that someone had the same issue as me on the S7 with the red lights and fixed it by just turning the LED's off and on, so I assumed it was just a bug. I'll definetly take a closer look if it happens again though.

And it's totally fair enough to check I'm not acciedently on WiFi! Just to be sure I disabled the WiFi card and made sure it wasn't running during the speedtest. I honestly wish I'd made a mistake like that but sadly I am definetly testing over ethernet.

  @Alexandre.

After borrowing a friends laptop with a gigabit ethernet port I followed your troubleshooting steps. I started by factory resetting all Decos, just to sort out the weird red light problem and an issue I had with the app. I placed the Deco into AP mode, and this time the light was white, so I ran the speedtests using a Cat5e cable:

Modem: 911/100

Main Deco: 576/98

I then switched to a different ethernet cable (the one that came with the Deco):

Modem: 945/100

Main Deco: 500/99

I finally ran the speedtest again from the Main Deco from a different port on the back, and it made little difference (563/102).

At this point I'm not really sure where to go. I'm pretty happy with the Deco S7 other than this issue, the WiFi is great for me and everyone else in the house, and I can't afford a different/higher-end model just to fix a problem which only effects me in the house. So for now I guess this will just have to go unsolved, 5-600Mbps is still the fastest WiFi I have ever had. If you do think of anything else to try though please let me know.