@Rcf026 I believe the main reason to disable the old SSID is to ensure that devices use the new SSID, because the new one offers a better coverage and transparent roaming.

Something else: it is usually recommended to avoid having two cascaded "routers".  Hence it is perhaps better to either run the AT&T router in "bridge" or "transparent mode", either run the Deco in AP mode.  I am not sure the AT&T router will keep its wifi active if you change its mode of operation.

yves_b wrote

  @Rcf026 I believe the main reason to disable the old SSID is to ensure that devices use the new SSID, because the new one offers a better coverage and transparent roaming.

 

Something else: it is usually recommended to avoid having two cascaded "routers".  Hence it is perhaps better to either run the AT&T router in "bridge" or "transparent mode", either run the Deco in AP mode.  I am not sure the AT&T router will keep its wifi active if you change its mode of operation.

  @yves_b Not a tech guy here so I understood about half of what you said. Forgive the long response, but I think I need to clarify my question. 

When I first set up my tp-link mesh network I connected the main X55 to the router by Ethernet cable. The other two X55's connected wirelessly. I used the same SSID name used by the AT&T router. When the mesh network went live I thought the client devices would recognize that SSID name and automatically connect to the strongest nearby signal. But they didn't. The app showed no client devices, even when I reconnected some of the clients to the SSID.
 

I then reset the X55's and set up the network using a different SSID from that of the AT&T router. Now when I connected the clients to the new SSID they were all recognized and showed up in the app as assigned to the nearest X55. This is how the instructions say it should be done per the tp-link Deco X55 set up video in the link below where they use the SSID name Deco to create a new network.

https://youtu.be/kmpAfA7KCn0?si=zQiO6phqmbRcJYNv

So, to make a long story short, I have followed the setup instructions to the letter, and my new tp-link X55 network is running fine. However,  the AT&T SSID is still live and there is no mention in the instructions of what to do about that, or if that is even something one needs to address. That is what I am trying to determine. 
 

PS What exactly do you mean by "run the AT&T router in bridge or transparent mode? 

  @Rcf026 

If everything works well, and if some devices are still using the old SSID, you can leave it running.

The video shows how to create a new wifi network from the Deco.  It would have been possible to migrate an existing wifi network onto a set of Deco, and it is too late for you to do that, as you modified the configuration of your devices.

If everything works fine, I would not change anything for the time being.  Having cascaded routers is not an issue except for specific cases.  By "run the AT&T router in bridge or transparent mode", I meant changing the setup of the AT&T modem, I believe AT&T calls that "passtrhough mode".  Again, if everything works fine, it is not worth making changes and, posisbly, injecting problems.

  @yves_b 

yves_b wrote

  @Rcf026 

 

If everything works well, and if some devices are still using the old SSID, you can leave it running.

 

The video shows how to create a new wifi network from the Deco.  It would have been possible to migrate an existing wifi network onto a set of Deco, and it is too late for you to do that, as you modified the configuration of your devices.

 

If everything works fine, I would not change anything for the time being.  Having cascaded routers is not an issue except for specific cases.  By "run the AT&T router in bridge or transparent mode", I meant changing the setup of the AT&T modem, I believe AT&T calls that "passtrhough mode".  Again, if everything works fine, it is not worth making changes and, posisbly, injecting problems.

Thank you. I definitely didn't want to get involved in changing the set up of the AT&T modem. That is definitely above my pay grade. It wasn't that hard to migrate the devices. I have none connected to the old SSID since I want each client to use the strongest signal available from the nearest AP, and I also want to keep track of the clients on the network through the app. Besides, the new SSD provides my family with a more user-friendly name as opposed to the AT&T router that uses a random mix of letters and numbers.
 

It was interesting to see how the strength of the two SSID signals compares at the furthest points out. The nearest tp-link AP definitely provides it's clients a stronger signal as compared to the signal coming from the AT&T router across the house. The AP's are doing their job. I assume now that I have migrated the client devices to the new SSID when it comes time to upgrade the system I can simply use the same SSID/password and the clients should theoretically find it. Yes?

By the way, since you brought it up, under what circumstances does it become an issue to have cascaded routers?

  @yves_b Update. It doesn't seem as though disabling the Wi-Fi on the AT&T router is that difficult after all. I found a really good video on YouTube that explains how to do it. See the link below. Apparently, to answer my own question the issue with cascading routers is potential interference, which does affect the new signal. I'm going to disable the AT&T Wi-Fi tomorrow. Hopefully it will go well. 
 

https://youtu.be/AE3afzRyNDc?si=HJBXNgVGlig7XMxt

  @Rcf026 

Next time you upgrade the system, you can, indeed, keep the same SSID/password, and the clients will find it.

Disabling the wifi on the modem will no stop the modem to act as a router.  Possible issues with cascaded routers:

• when the Deco acts as a router, clients connected to the Deco will not be able to communicate with clients connected to the modem
• some usage, such as peer to peer, requires changing the configuration of the router(s), and, sometimes, do not work via two routers

Disabling the wifi on the modem will no stop the modem to act as a router.

  @yves_b I meant disabling WiFi operation of the router, not simply disabling the broadcast of the SSID. This seems to be something recommended by tp-link, and many others once the mesh network is operational so the signals don't conflict. I did find that on a couple of occasions when I navigated to network optimization on the app and conducted a scan it reported another network with conflicts. After optimization the issue was gone, but soon it returned. Hopefully disabling the WiFi configuration of the AT&T router will resolve this.

  @Rcf026 It is, indeed, a good idea to disable WiFi operation of the AT&T router.

The AT&T router will continue acting as a router.  It will probably not impact your usage of the network.

yves_b wrote

  @Rcf026 It is, indeed, a good idea to disable WiFi operation of the AT&T router.

  @yves_b  I think so as well. After disabling the router's WiFi the optimization scans have detected no interference. I appreciate your help, and I hope this thread will helps others researching the same issue. It should be noted that as shown in the video I posted before there is a difference between turning off the router's broadcast of the SSID, and disabling the router from operating in WiFi mode. The former will still broadcast the signal without making the SSID visible. The latter will disable the router WiFi altogether only allowing connection to the old network via Ethernet cable. That is what needs to me done in this case. 
 

Thanks again!