@pavel_105 

Deco mesh runs in either Router or Access Point mode. There is single setting in Deco app for all of Deco units in your household, so whatever you choose will apply to the whole mesh you have.

Deco app screen with that setting:

You need to decide if you will be running Deco in Router mode (default setting) or in Access Point mode. If you are deploying Deco primarily to improve WiFi coverage, I would recommend Access Point mode. See What’s the difference between Access Point mode and Router mode on the Deco?

If you decide to run Deco mesh in Access Point mode, you can wire Deco units any way you want. You would not even need to pass all your home Internet traffic through Main Deco on its way to TD-W9970B router. I would recommend reading this document: General questions about Ethernet Backhaul feature on your Deco

Additional benefit of Deco Access Point mode is you would not need to make any changes on TD-W9970B router, other than turning off its WiFi.

If after reviewing these documents you've decided to stay with Deco Router mode, feel free to ask follow up questions. 

@Alexandre. Thanks for reply.

I was planning to do the AP mode setup as an alternative, if router mode won't work out. AP mode does seem to be the easiest solution and probably most reliable too. However, i will have 4 ip cameras that will record 24/7, and then there's also other internet activity, and the problem with my current router is that it seems to have only 100 mbit lan ports, which means that i will still need to bridge to another router with faster lan ports.

So far 3 question regarding router mode:

What to do with DHCP on my root vdsl router after i bridge it to Main deco? Should i switch it off or just leave it on, basically it will give just one ip: to the main deco unit.

Quote:

"There is single setting in Deco app for all of Deco units in your household, so whatever you choose will apply to the whole mesh you have."

Is there no option to set each unit individually?

If there's an option to set each unit's mode individually, which is better:

root router bridge --> main deco in router mode --> all other decos in AP mode

root router bridge --> main deco in router mode --> all other decos in router mode

@pavel_105 

I think we should clarify terminology first.

Deco mesh in Router mode: Main Deco is your router and Satellite Decos behave as access point nodes, for Main Deco. You do not need to configure anything on Satellite Decos, they will automatically understand their role. 

This is what you will have: root router TD-W9970B --> Main Deco in Router mode --> Satellite Decos as access point nodes

Deco mesh in Access Point mode: ISP router is your router. While Deco mesh runs WiFi under its own SSID, all Deco nodes (Main and Satellite) behave as access point nodes for your ISP router.

Hopefully it is clear now, but if not, feel free to ask for additional clarification.

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Your planned setup should work with Deco mesh running in Router mode. At least initially, leave your TD-W9970B router as is. Don't change it to bridge mode, don't disable its DHCP. Just turn off its WiFi after you setup Deco mesh.

You will have traffic going to Internet through two routers: Main Deco and TD-W9970B. This is called "double NAT" and in most cases is not noticeable for apps and devices. Notable exception is XBOX, also some VPN services. Google "double NAT" for additional info, but generally speaking: if you set up Deco mesh in Router mode, with your current VDSL router, and everything you use accesses Internet with no issues - there is no reason to mess with TD-W9970B.