@Kathyh When you have to use an ISP router it's better to set Deco in AP mode as you did to avoid the double NAT in your LAN. Now what I've understood from your post is that you need to use the Deco...

@1382-837366__71 This router model (TL-WR850N) is not supported by the Tether app - here's the tether compatibility list.

@DanQo I guessed that you want to limit the bandwidth of a particular device which is a different feature - Bandwidth Control. That's why I tried to explain what QoS is and how it works. TL-WR820N...

@NGSC Check this post which gives an answer to both of your questions.

@DanQo You need to understand what QoS is: "The QoS (Quality of Service) feature allows you to prioritize the internet traffic of specific devices to guarantee a faster connection when you need it...

@RichStaf If I understood correctly you need a different DNS server on the LAN side of the TP-Link router. If that's correct you can do that here: