Deco M5 internet connection down but main router working
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I had a very strange problem last night which lasted about an hour. I have not changed anything recently, I was not doing anything to the network at the time.
I have 5 M5 Decos running in AP mode connected to my Plusnet Hub One router. We were watching streaming TV when it stopped because the network went down, I could see the deco next to the TV had turned red. This usually indicates that the main router has lost connection or has rebooted for some reason, but when I checked the router, it was fine.
Using the main PC which is connected by cable directly to the Plusnet router, I found this:
The internet connection was fine, I could call up the router admin pages from the PC, and I could also access the internet normally, and speedtest showed the line was working at normal speeds (we have a very good phone line, 74 down, 18 up). But the really strange part was although all the decos had a solid red light and nothing connected to them could get to the internet, the router COULD see all the devices, and indeed I could ping them from the PC.
I went through several reboots of the router and of the whole deco network, and tried swapping ethernet cables and using different ports on the router and the main deco, but they all remained red. Then after about an hour of messing around and getting nowhere, they finally turned green, and everything worked again, and has done since.
So my question is, precisely how do the decos determine that the internet is "available"? Is there a server that they connect to that maybe had a problem last night, so they determined the internet was not available even though the connection was actually fine?
I don't understand how my PC could access the internet, the main router was online to the internet, on the local network the router and the PC could see all the devices which connect to the decos (I run a home assistant system on a raspberry pi which is connected to one of the decos, and I could even access that webserver from the PC so it was clearly talking to the router), but the decos would not "allow" any connected devices through to the internet?
I have Deco mesh running in AP mode, two M5 and two M9 Plus, and have been playing with Adguard recently. In my case, I have configured my ISP router to provide Adguard DNS service as DNS server address for every client on my home network, including Deco units. This did not cause any issues with Deco. I suspect, the issue you see is not related to Adguard.
Just for the reference, the list of filters I've enabled in Adguard I am running:
