@RoomTiger 

 

If you decided to return your Decos to the seller, remove them first from Deco mesh, in Deco app. As a courtesy to whoever else will end with your "slightly used, excellent condition" Deco units.

 

You have ended with bricked Deco unit, unless you can recover it not much else you can do. Try resetting it again, according to TP-Link manual. See article Deco M4 became brick during update? If nothing helps or you don't want to bother, returning that Deco set is only option. What else you can do.

 

I am assuming you've already restored your home network to what it was before Decos. Will continue under that assumption.

 

If you recovered your Main Deco, or if after returning that set you've decided to buy another set of Decos and try again, these would be my recommendations on how to deploy them.

 

You have more complex that average home network, so ask yourself if you want Deco mesh for WiFi coverage or for other features. I, too, run file server, also I have backup server and print server on my home network. When I got Decos I configured them to run in Access Point mode. They provide excellent WiFi coverage over my house, and the rest of network runs undisturbed.

That would be my suggestion: instead of running Decos in default router mode, configure them in Access Point mode. That'll make your life much easier.

 

In case you want such features as parental controls, traffic filtering, antivirus - that would be Deco in router mode. You were almost there, your "Second Setup," when you went the wrong way with troubleshooting.

Next time, if you deployed mesh and it runs file, but single device (NAS) can't connect to it - instead of messing with mesh focus on that device. You got it right that it probably stuck to its old IP address, but if you have figured how to unstuck it or how to force it request new IP address - you'll be done with setup. 

 

That would be my suggestion for next time: go after NAS, search for forums of NAS users, google it - you can't be the only one whose DS220+ NAS can be stubborny stuck to its old IP address.

If it is stuck with old IP and not visible when connected to Deco, bring back ISP router in router mode, plug NAS to ISP router, gain full access to its configuration settings online, and start from there.

After done, ideally by removing DHCP reservation from ISP router, ensuring NAS gets dynamic IP address after each restart, plug NAS back to Deco.

 

After you managed to make NAS get IP address from Deco IP range, you can make it static by going through Deco router configuration settings and making DHCP reservation for NAS that Deco mesh now sees.

I've tried again, this time without messing with the deco's settings. Seems to be working surprisingly well after I let it "sleep" for a night :

- put the secondary deco as main after a reset, worked well. The other one wouldn't connect after several attempt but I let it "sleep" the night and this morning it was connected ^^

- removed every static configuration on the NAS and temporarily lowered its MTU on a friend's advice

- kept the router mode of my modem (I'm not sure why it's not on bridge mode I may have just forgotten to reboot it yesterday evening)

- This morning after booting up the NAS, no change in its IP (still on the modem's network) but weirdly enough it is detected on my computer which is not on the same subnet.

 

The double NAT seems to be working well without blocking anything now. I don't get how.

Will see for a while how it works I'm afraid to put it in bridge mode now

 

Thanks to both of you for your help, really appreciate it.

Update : As I feared, putting the modem back in bridge mode brings everything down.

VERY unstable wifi and cable connection with DNS errors. Cannot connect to decos using the app, even with reboots its light stays solid red.

The NAS was offline, so not his fault.

As soon as I put the modem back in router mode, green light on the deco.

Edit : It has been confirmed that the culprit is a broken bridge mode on my ISP's modem. Bummer. I'm forced to use the router mode.

 

Can I keep both in router mode ? What are the drawbacks if any ?

Maybe I can use a DMZ on the modem in router mode instead ?

@RoomTiger 

Edit : It has been confirmed that the culprit is a broken bridge mode on my ISP's modem. Bummer. I'm forced to use the router mode.

Can I keep both in router mode ? What are the drawbacks if any ?

 

So the guess that something in your system was broken was correct then. I would just go back to router mode, you already confirmed that double NAT didn't cause any problems.

Well it does now... My ISP lists an IP and MAC adress for the deco that is not the one in the TPlink app (1 digit different)... So I'm having trouble forwarding a port from the modem to the deco to the device... I'll have to try access point mode and forget about all of the Deco router functions. I hate to pay for a product I can't use fully... Damn ISP Any advice to switch to access point only ?

@RoomTiger 

 

Deco unit has multiple MAC addresses, because it has Ethernet card and wireless. The one that is on the bottom sticker of device is its Ethernet MAC address.

 

Still, I am not sure what MAC address has to do with port forwarding. Port forwarding done by the router (Main Deco in your case) using destination IP address inside the network and port number(s). You usually need that only if you run server you want to expose to the Internet.

 

You may be able to get help here if you can describe what you want to achieve instead of what you are doing. 

 

Example: "I have Web server running on my home network, I want it to be accessible through ports 80, 443 and 8080 from the Internet."

 

@Alexandre.  Got what I needed by switching to access point mode.

A bit sad to lose all the router functionality of the decos, but that will do for now, at least I don't have any double NAT problems now...

Thanks a lot to everyone who helped here !