Deco M5 internet connection down but main router working

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Deco M5 internet connection down but main router working

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Deco M5 internet connection down but main router working
Deco M5 internet connection down but main router working
2023-09-14 11:54:46 - last edited 2023-09-15 18:48:27
Model: Deco M5  
Hardware Version: V3
Firmware Version: 1.7.1

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?

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Re:Deco M5 internet connection down but main router working-Solution
2023-09-15 18:48:03 - last edited 2023-09-15 18:48:27

  @David-TP I have figured out what happened. Apparently there have been massive problems over the past day or two with the Plusnet dns servers, this would explain why the decos suddenly couldn't get at anything and marked the Internet as down. As there is no way of overriding dns settings in the plusnet router, there's no easy way around that - the pc I was using to check was specifically configured using either my adguard system, or 8.8.8.8 so I didn't see the problem. 

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Re:Deco M5 internet connection down but main router working
2023-09-15 07:56:41

  @Meshdave 

Hi, Have you set up any DNS filtering on Access Control on the main router?

Deco would make online internet detection by sending some DNS requests to several common domains, like Google/Amazon, etc. If the DNS resolution succeeds, the LED would remain green, otherwise would turn red.

Both Decos and other network services/devices still have IP addresses from the DHCP router and are also under the same IP range so the PC does not need internet access to ping the local LAN devices.

 

Thank you very much and best regards.

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Re:Deco M5 internet connection down but main router working
2023-09-15 15:26:27

  @David-TP Hi, no nothing like that, I haven't changed any router settings for years. From the PC (connected direct to router) I could not find anything wrong, but the decos were adamant the connection was down, even though they were clearly able to talk to the router (several restarts of the deco network, including powering off the main deco, resulted in all the local devices, around 45 of them, re-connecting each time and being visible to the router and the PC).

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Re:Deco M5 internet connection down but main router working
2023-09-15 15:33:27

  @David-TP One further thought - I have been experimenting with Adguard running on my Home Assistant machine (an advert filtering DNS server), but I have not configured the router to provide this as a DNS address to clients (it's not possible on the Plusnet Hub One) so the only machine that has been using it is the main PC where I have manually configured the adapter DNS settings to use it. It had been running for a few days before this problem, and it is still running now, and the only thing it reports as having used it is the PC, but is it possible that the decos do some active sniffing around for local DNS servers and possibly found this and started using it temporarily? Even if they had, I don't see why they wouldn't be able to find any of the services you mention, but it is the only possible thing I can think of that might have interfered.

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Re:Deco M5 internet connection down but main router working
2023-09-15 15:43:04 - last edited 2023-09-15 15:45:28

Meshdave wrote

  @David-TP One further thought - I have been experimenting with Adguard running on my Home Assistant machine (an advert filtering DNS server), but I have not configured the router to provide this as a DNS address to clients (it's not possible on the Plusnet Hub One) so the only machine that has been using it is the main PC where I have manually configured the adapter DNS settings to use it. It had been running for a few days before this problem, and it is still running now, and the only thing it reports as having used it is the PC, but is it possible that the decos do some active sniffing around for local DNS servers and possibly found this and started using it temporarily? Even if they had, I don't see why they wouldn't be able to find any of the services you mention, but it is the only possible thing I can think of that might have interfered.

  @Meshdave 

 

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:

 

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Re:Deco M5 internet connection down but main router working
2023-09-15 15:54:15

  @Alexandre. Thanks, I can not think why Adguard would cause a problem like this anyway, but it is the only change I have been testing recently. As I said, my router does not allow DNS settings to be changed, so it would not have been given out to anything, including the decos, only my PC is configured to use it at the moment.

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Re:Deco M5 internet connection down but main router working-Solution
2023-09-15 18:48:03 - last edited 2023-09-15 18:48:27

  @David-TP I have figured out what happened. Apparently there have been massive problems over the past day or two with the Plusnet dns servers, this would explain why the decos suddenly couldn't get at anything and marked the Internet as down. As there is no way of overriding dns settings in the plusnet router, there's no easy way around that - the pc I was using to check was specifically configured using either my adguard system, or 8.8.8.8 so I didn't see the problem. 

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