[EdLUG] Network problem

[Andrew Kember]

On Sat, 13 Feb 2021 at 11:47, Dick Middleton <dick at lingbrae.com> wrote:

> I've got a really weird problem with my network and I'm at a loss as to
> what to do.
>
> Just after midnight on Thurs problems were noticed.  Things stopped
> downloading from the
> network.  But not everything.
>
> No problems are being seen with Chromebooks and Android phones (wifi) but
> iPod, TV,
> network streamer etc have stopped working.
>
> My main linux desktop computer has no problems but a couple of arch linux
> computers do.
>
> I've narrowed it down using curl; on working systems curling a webpage
>     curl -v http://mirror.bytemark.co.uk I get the index page
> on a non working system it returns nothing - it just hangs waiting.
>
> If I provoke a 404
> curl -v http://mirror.bytemark.co.uk/x then all systems return an error
> web page.
>
> Similar effect with nc
>
> printf "GET / HTTP/1.1\r\nUser-Agent: nc/0.0.1\r\nHost:
> 127.0.0.1\r\nAccept: */*\r\n\r\n"
> | nc mirror.bytemark.co.uk 80
>
> It looks like a routing error but if that was the case all systems would
> fail and the
> error page would also not be returned.
>
> My brother has simple home page which is returned normally from all
> systems; again
> suggesting it's not a routing problem.
>
> I'm totally perplexed and would really appreciate some ideas
>
> Dick
>
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One cause that covers some but not all of your problem statement would be a
device in your house on your network advertising itself as the default
gateway. Different device types might pick up that info at different times
or rates, causing the kind of issues you're seeing.

One example of this that happened to me is a new smart, network-connected
LED controller that we bought. The setup routine was ... extremely janky.

The way it was supposed to work was that it initially created its own
wireless AP. You connect your phone to that (this is when it should be
advertising itself as the default route) and give it details of your WiFi
ssid and password.

It's then supposed to connect to your normal WiFi, turn off its own AP
function and - crucially - stop telling everything in range that it's the
default gateway for the internet.  That last bit didn't happen.

As a result, devices in the house just mysteriously stopped connecting to
the internet.

It's a long shot, but I thought I'd share my experience. Hope you find the
cause!

Andrew Kember.

(P.s I've attempted to bottom-post my reply via GMail on iOS, so apologies
if this turns out badly)

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