Sign in prompt required, please help

[#1]

This is a strange one. I'm certainly not the most knowledgeable when it comes to networking, but I have a little experience. Myself and a good friend who currently works as a contractor with a networking background have brainstormed all we can and are yet to determine the problem.

Last week we had a power cut, possibly also a surge when it came back on but I am unable to confirm that. Ever since, accessing the internet on any device (both wi-fi & ethernet) gives the "No internet, requires sign in" message, (slightly different wording across different devices, but it's the common prompt you get when you need to sign in to free public wi-fi etc.)

Immediately I thought this was just a rather simple and shallow DNS issue, possibly with ports getting a little messed up due to the abrupt outage, also at one point I believe sites and apps that commonly use UDP were working, and TCP based https services were not, so I thought I had caught the problem immediately.

But it has been days now, as I said I've spoken with a friend who knows a little more than me and we've essentially tried everything I can think of, (I'm well aware I could be missing something really stupid and embarrassing myself right now). The usual basic stuff first of course, power cycling every device involved, then factory resetting the hub. I've been all through the admin settings in the hub's portal, ran a bunch of ip and dns troubleshooting, I just can't fix it.

The immediate affects are also a little strange, at least to me, someone who hasn't experienced this exact issue before. Internet access is pretty much perfect, on most devices it doesn't even block anything, it just shows the message. (On my PC for example, it just constantly shows "No internet access", but I have full access unhindered. It's only really annoying on the TV and on Alexa's where they basically just don't work, haven't found a way past it yet.

I obviously have my ideas, my guess is simply that either the modem or router got damaged from the cut/surge, but I'm of course curious if anyone knows of any other possibilities before I need to start thinking about replacing certain hardware etc.

I'd appreciate any help or advice and I'm willing to discuss and provide any extra details, thanks :3

[#2]

You're not alone. Same issue with me for couple of days. Really weird!

[#3 · Accepted solution]

It doesn't sound like an electrical damage sort of problem to me.

My best guess is that for some reason the check that devices make to detect if a device is connected are failing.

A Microsoft "Dev Blog" article says:

"Windows attempts to download a file from a dedicated Web server. Depending on which version of Windows, it’s http://www.msftncsi.com/ncsi.txt or http://www.msftconnecttest.com/connecttest.txt. If the download is successful and contains the correct contents, then Windows concludes that you have full Internet access.

If something goes wrong, Windows will report either limited or no Internet access, depending on what exactly went wrong."

For me, a tracert to this address ends up at 2.19.252.163 after a good bounce around in Akamai's systems.

Try this kind of test when you see the message (to the test address for the device) and see what the result is.

Rubbing the crystal ball a little more, I wonder if the power bump caused you to move IP address within Plusnet to a range with a bit of a routing problem.

[#4]

For anyone experiencing a similar problem, I will do my best to briefly explain the solution. While this response wasn't exactly the fix itself, I do deeply appreciate your help, the tracert was something I was going to do but forgot and you definitely reminded me. Technically that allowed me to see where the issue was, because it was simply a backend authentication issue, and the trace route showed me that my ping reached the destination, but got intercepted along the way by a flag.

That flag was just fixed, I finally got through to someone on support that was very nice, kind and helpful. Apparently it was some sort of failed authentication flag that as visible on my account. They hinted that it was an issue possibly triggered by my power outage, but that a lot of other people have been experiencing the same issue recently, (I believe it might be linked to the same flag put on your account if you fail to pay your bill? Idk they didn't explain it much even when I asked)

The flag was removed and all is now fixed :3