For both questions, in AP MODE, the anwser is YES, Deco has support for this topology. In router mode you get red lights on Deco 2 and 3.

Configure all decos before via wifi, afte this and network ready proceed this step:

1. Turn on 1st Deco, wait green light.

2. Wire and turn on Deco 2, if green light apear, Backhaul working.

3. Do same action on Deco 3.

Now this gets interesting

I sent in a support ticket before posting here on the forums and the official TP-Link response is as follows:

*Note: I provided them with the same layout etc.

===========================================

Thank you very much for your valued reply.

If you need to get a mesh network and running Ethernet backhaul, you can configure deco as router mode or AP mode. So your current topology is not correct mesh network, so even you connect them to each other , they don't run Ethernet backhaul. If you need to set the deco as AP mode, you should connect like modem---router---deco1-deco2-deco3, or modem--router--deco1-switch--deco2(deco3). any way, you should make sure one of the deco is connected to your router directly.

In the following FAQ, the deco is working as router mode:
https://www.tp-link.com/us/faq-1794.html

In the following FAQ, deco is working as AP mode:
https://www.tp-link.com/us/faq-1842.html

Thank you!

Have a nice day!

===========================================

This seems to suggest that my method of connecting up the DECOs DO NOT adhere to their definition of a mesh AP network using Ethernet Backhaul. 

They reference https://www.tp-link.com/us/faq-1842.html in which the layout for the AP mode with Ethernet Backhaul shows that DECO M5 (UNIT 2) and DECO M5 (UNIT 3) needs to connect to the 2nd ethernet port of DECO M5 (UNIT 1)

The following is mine, which they claim is incorrect.

FIGURE-1

                                                                 |-------------> DECO M5 (UNIT 3)
                                                                 |

WWW ---> MODEM ---> ROUTER ---> SWITCH ----------> DECO M5 (UNIT 1) (MAIN DECO)
                                                                 |
                                                                 |------------> DECO M5 (UNIT 2)

They need me to admend to the following

FIGURE-2

WWW ---> MODEM ---> ROUTER ---> SWITCH -----> DECO M5 (UNIT 1) (MAIN DECO) ----> DECO M5 (UNIT 2) ----> DECO M5 (UNIT 3)

But who has existing network cabling done like this? 

:confused:

I wonder if I were to complex the setup and run it like this, what will be the effect?

FIGURE-3

                                                                |-------------> DECO M5 (UNIT 3)
                                                                |

WWW ---> MODEM ---> ROUTER ---> SWITCH ----------> DECO M5 (UNIT 1) (MAIN DECO) <------|
                                                                 |     |                                                                                    |
                                                                 |     |-------------------------------------------------------------------|
                                                                 |
                                                                 |------------> DECO M5 (UNIT 2)

Any ideas?

Tested this over the weekend.

(a) Setup as per Figure-3 

DECO M5 (UNIT 1) (MAIN DECO) went crazy, from the switch, lights were blinking non-stop. Think it created a loop of sorts. DECO's light also turned RED. No internet access. Disconnected it.

(b) Setup as per Figure-1

1. Connected wirelessly to DECO M5 (UNIT 2)

2. Ran a speedtest against the local ISP server. Got about 670Mbps. My subscription is for 1000Mbps. 

3. Disconnected the Ethernet cable on DECO M5 (UNIT 2)

4. While still connected to DECO M5 (UNIT 2), ran the speedtest again

5. No internet access

6. DECO M5 (UNIT 2) light turned RED

(c) My Personal Conclusion 

- The setup in Figure-1 works as per what LEOGZ mentioned

- Not sure why TP-Link Support is insistent that it does not

- Out of the box, my setup summarized as follows:

1. Power up DECO M5 (UNIT 1)

2. Setup DECO M5 (UNIT 1) as per the TP-Link App (Setup wireless SSID, password, etc.)

3. This puts DECO M5 (UNIT 1) into ROUTER mode

4. Add in DECO M5 (UNIT 2) to the setup

5. Add in DECO M5 (UNIT 3) to the setup

6. Test Internet accessibility

7. Update all the firmware

8. Change DECO M5 (UNIT 1) mode to AP 

9. Power off DECO M5 (UNIT 1), DECO M5 (UNIT 2), DECO M5 (UNIT 3)

10. Move DECO M5 (UNIT 1), DECO M5 (UNIT 2), DECO M5 (UNIT 3) into position, plugging in their respective ethernet cables as per Figure-1

11. Power up DECO M5 (UNIT 1)

12. Power up DECO M5 (UNIT 2)

13. Power up DECO M5 (UNIT 3)

14. Test and enjoy internet connectivity

- That's my setup for TP-Link Deco M5 in AP-Mode using Ethernet Backhaul.

 

@thankgod 

Is your setup still working?

Last week i installed this system (m5) as follows:

m1 (main Deco) directly on the modem (main level). M2 and M3 (upstairs, first and second Floor) via ethernet backholes, which are directly connected to the modem. Setup of M1 in accesmode. 

Worked perfect.

All of sudden, my ethernet connection in m2 and m3 collapses today,  and m2 and m3 are using the WiFi signal of M1 which results in poor internet.    

Furthermore i found out that m1 was back in routermode again. Now i can install it all over again, but if this will occur every week i need to find a solution. 
 

can anyone give me an advice on this matter?

@thankgod just a clarification.

In the topology of Figure 1, there is only one wireless network (SSID name) for the whole house right?

I'm just trying to figure out how to make my topology for optimizing wifi with ethernet backhaul.

Thanks 

@thankgod I was surprised by the reply of Customer Service at the time.

AP Mode with switched Ethernet backhaul between master and slave DECOs is supported;

https://www.tp-link.com/uk/support/faq/2399/

How are things working for you these days?  Is the wifi client handoff working well between APs?

Cheers,

James.