Router acts weirdly on DHCP and phones drop connection suddenly and randomly recently

[#1]

Hi,

I am experiencing weird things recently with my router. I have an unusual setup but it did work for more than a year before I started to have issues. I hope someone can help me as it is a tad annoying - you'll understand when I explain the allowance bit

Setup:

I have the plusnet fibre broadband router as the main router with 2.4ghz wifi allowed only. Also I have an old sky router upstairs linked into the plusnet router with a LAN cable. This upstairs router is an access point only for extending the wifi. I have a tinfoil like underlay upstairs which is screening out the downstairs wifi almost entirely hence I needed an additional router there.

In terms of the upstairs router setup I have set it on a static IP and the plusnet router doesn't even show this router on the DHCP table. SSIDs are the same. Every wifi connection going through the upstairs router are shown as LAN connections on the plusnet router page. (plusnet router deals with the DHCP table and dynamic IPs)

Here is what I do experience:

Phones are dropping the wifi connection and they can't reconnect. I can't remember to have experienced the same with laptops. I have to reboot the rooter and the phone as well to reestablish connection. (or wait a very long time, probably hours to have it resolved on its own) Also the weird thing is when I look at the connected devices the phone in question is shown as connected however strangely the laptop I am doing the check on is not shown on the connected devices list nor on the DHCP list but it works. (I just noticed this today, previously my laptop used to be shown as it should)

What I know / have tried:

In the past year a few times (2 or 3 times altogether) my wife's old phone got being "stuck" on the connection list. When we go down stairs the phone has to reconnect to the downstairs wifi and vice versa. That old phone got stuck in the connection list and blocked the IP address resulting in a connection issue while trying to connect to the other router. This was resolved by kicking out the phone manually from the list. This never ever happened to my phone (which was a better model).

In August I was watching youtube on my phone and out of the blue I received a message from my phone provider that my allowance was used fully. My contract month just started and I didn't use any of my allowance for that particular month so far. I then realised that the wifi icon completely disappeared from the phone. It could not connect to the router at all. That was the first instance of this issue. That particular night I just went to sleep without trying to fix it and by the morning wifi was up and running again on the phone, so it resolved itself during the night.

I thought it was a one off, but unfortunately it happened a few times since on both my and my wife's phone. Wifey's phone just did it again hence I ended up writing this post after spending hours trying to fix the router.

Some additional notes:

- I am positive my laptop is not on the list I have checked MAC and IP, no match.

- The issue is not related to going upstairs or downstairs. It can be that I am upstairs for hours and it just happens.

- The issue is not related to the wifi signal strength or interference.

- I have found in a thread that someone complained about the router upgrade. I never knew it happens automatically but since I read that topic I have checked mine. It was last updated on the 15th of August. My allowance was eaten up on the 24th of August in one go. (I still have the notification text message) May have no relation but with this I couldn't rule out the update as a possible culprit.

- I wouldn't think (but not ruling out either) that the upstairs router is faulty as it seems to me that the plusnet router's DHCP handling is the one that doesn't work properly any more.

- I cannot reproduce the error therefore I am unable to do extensive tests. The wifi drop happens randomly, I couldn't identify any cause or pattern

Sorry for the long post, I hope I managed to answer a few of your questions in advance.

Any ideas welcome, if you want to have more details on my setup/issue etc I am happy to share. I need a solution because we have low internet allowance on the phones and it is basically impossible to notice when the wifi icon suddenly disappears and internet switches to mobile data especially when it happens during watching videos. Waiting almost a month for the allowance to reset is a nightmare

[#2]

So the fundamental problem is that your phones(s) sometimes lose your home WiFi connection, switch to mobile data and then rapidly consume your monthly allowance?  Isn't the best thing to do to turn-off mobile data when you are at home, or at least when you are at home and about to watch a YouTube video?  See for example: https://www.techadvisor.co.uk/how-to/google-android/how-limit-data-usage-on-android-3509785/

Although it is convenient to use the same SSID for both your wireless networks, you then never know which network your device is connected to and at what point it decides to switch.  If you used different SSIDs you might get a clearer idea of what is going on/wrong.

You are setting great store by the absence or presence of a device on your routers list of connected devices.  I have never found that this function is particularly reliable on routers in general so I think this may be a red herring.

It may be possible to tether a mobile phone to your PC so the PC connects to the internet via the mobile phone's data connection.  You can also buy routers that connect via 3G/4G wireless rather than by cable or landline.  But I would be pretty surprised if it turned out that your Plusnet router had the capability to do that unbidden or bidden.  So I think the idea that your Pluisnet router sucked the data for its update though your mobile phone rather than through its own broadband connection is far-fetched.  And I doubt that the update consumes much data anyway.

[#3]

Thank you for your reply! I have the feeling I managed to confuse you a bit.

I didn't think the router did suck up my allowance. It was youtube I meant that while you are watching a video on the phone full screen you don't see if the wifi icon is there or not. That means if the wifi connection drops it automatically switches to mobile data on the phone but I won't notice that until it is too late. I had 500mb allowance previously so you can see it was quite easy to burn out with a few videos in no time. Now I have upgraded to 4gb but still I want to keep that allowance for the weekends when we go out and I use it for google navigation etc.

Switching off the mobile data all the time when I come and go is inconvenient and could cause trouble when I forget to switch it back on when leaving the house but expected to be available. I know it is an option but I would like to have it sorted rather than having this workaround.

Regarding the SSID if I wanted to use the upstairs router as a wifi extension only rather than as a separate network I had to use the same SSID. (can't really remember the details why the setup is as is, I did it over 2 years ago and spent days reading forums, articles, guides to make it work for me) This doesn't cause any issue at all. The screening between the floors works so good (unintentional that is) that if I switch off one of the routers I can't really use wifi on the other floor, signal is that weak. If I am not standing on the stairs somewhere I can tell exactly which router I am linked to, devices pick up the strong signal.

I take your advice on the DHCP list, I thought that is like written in stone

Basically what I am looking for here, I would like to understand why these wifi drops occur and how can I prevent them. Every time logging into the router and rebooting it along with the phone is far from ideal. Also this is a recent behaviour therefore it is fair to assume that something has changed that triggers the wifi drop. Again, that's why i mentioned the firmware change on the router, it may be a cause, I don't know. I did not change anything on my end, everything was up and running, I didn't touch anything. It can also be the phones' update, again something that I won't know. I am looking for ideas what I could check and how I could check those. Even better if someone else had the same and found a solution.

[#4]

I am 99% certain that as long as your two routers remain linked by a LAN cable then their wireless networks will never be unified, even if they have the same name.

WiFi is rarely rock solid.  A burst of radio interference can cause the connection to be dropped momentarily.  Nor is WiFi like mobile phone coverage where you can move from one base station to another without dropping the call; you presumably lose the WiFi connection momentarily every time you take a device up and down stairs.  If your mobile devices obligingly connect to 3G/4G whenever this happens then you have to decide which is more troublesome, manual intervention or loosing your entire month's data allowance.  

The tendency to lose WiFi could be indicative of a problem with the router's WiFi.  So if it happens downstairs then it's a problem with the Plusnet router and if it happens upstairs then the Sky router is to blame.

[#5]

Just for future reference in case anyone else runs into similar issues.

The secondary router was the faulty one. I had an old ASUS router lying around (it was half bricked hence I went with the sky router first) and replaced the sky router upstairs with it. It has been tested for about a month now and the issue never came up since. I did not change anything else, ASUS router was set up to the very same as the previous router was.