In my case the problem was the ethernet cable. All cables where CAT5e.

My setup is like this:

2 Deco M4, first working as the main router, and another one as slave (Mode: Wireless Router)

Tried all the settings for QoS, limit to 1000mbs but didn't work.

I contact support and they told me to try to check to Status of the connection to see what speed it showed. 

Connected to second Deco by ethernet it showd 100 Mbps. Connected directly by ethernet to main Deco it Showed 1 Gbps. 

By replacing the cable that was from the second Deco to my PC/laptop i resolved the problem. It seems that the cable wasn't made properly for the RJ-45, if i'm not mistaken, and the color of the wires didn't match at the end (cable from deco 2 to pc didn't match the cable from main deco to deco 2). If the cables are not wirred properly the device will not send the data correctly and that's why it's capped at 100Mbps. I don't remember exactly the explanation. The initial cable was bought as it is, i didn't do anything to it.

Hope it helps.

Hello, 

I just bought a Deco M4 and no matter what i do is capped at 100 Mbps. 

I'm using a Master and a slave , the master is directly connected to the internet. I switched them around without success. I use a cat5e cable between the master and the slave. 

Strangely i managed to get around 500 Mbps on a speed test on wifi when i switched the cables around. 

PS : Just right now i disconnected the slave, rebooted the Master and now i get around 500 Mbps download and 436 Mbps upload on my laptop. I will try to change the cable between master and slave tommorow and see how that goes. 

LE : I changed the cable to a brand new cat6, i dissconected the slave, rebooted the master. Without the slave i get around 450 Mbps download/upload, i connected the slave i got capped to 100 Mbps. 

Thanks

  @TP-Link 

Any more ideas? The qos doesn't work. I have found that if i disconnect the slave, the master gets gigabit connection. I connected the slave and in 10 minutes both master and slave got capped. 

I think i'll return the product since i can't get it to work at Gigabit connection. 

Best regards, 

George

  @TP-Link 

Hello, 

Thank you for the reply and the ticket ( i received the email from you ). 

For the first question the answer is yes , they were both capped at 100 mbps. 

For the second question : I tried disconnecting the slave and rebooting the master. I got gigabit connection. This morning i gave it one more try, but this time i have rebooted both from the web app. For two hours the connection is gigabit for both master and slave ( they are still connected with the cable ). 

I'll get back to you with an update later on how they are performing. 

Best regards, 

George

  @George.Bran 

The issue is still present, for no reason the connection is capped at 100 Mbps. 

Best regards, 

George

  @PavanKumar I'm having the same problem,  speed at the first M4 in my mesh is capped at 100Mbs.  All 3 M4s are set up as access points only so I don't have Qos on my phone app.   Do I need to reinstall the mesh network so I can turn off during installation?  If not how do I do I disable Qos?  Thanks.  Driving me crazy!