[neon5077]

Here's my own 500 mile email story. This happened to me about a year ago.

Just a normal day at the office when suddenly the internet drops out, except for my machine. Everyone else has a network connection, but no internet. Except for me, I can't reach devices on the local network, but I can reach anything outside.

Now, our network is not large or complicated. We have a consumer grade ONT and WiFi router provided by the ISP, and a big unmanaged ethernet switch. There's really nothing to go wrong here.

After some debugging, I notice that I have been assigned an IP address in my ISP's public block. Tracert seemed to show no local network between me and the WAN. It was as if the router had somehow connected my WiFi client directly to the ONT, bypassing the local network. That only barely makes sense, but it was my best guess so I condemned the router.

Next day, new router, same problem. I couldn't explain it. This time though, I didn't have an internet connection, but local network was reachable. Some sanity restored, ar least.

Turns out that our fiber line had been accidentally cut during construction work. Once the ISP fixed that, all was normal.

The question remains, how did I have internet connection through a severed fiber line? It's not likely that the router had a bizarre failure right before the line was cut. I suppose it's possible that Windows had sneakily connected me to some other WiFi network, but then why did I have a weird IP address?

I have no explanations

[hunter2_]

Does your machine have a cellular modem that gets prioritized only when there's no route to some well-known service via the normal network adapter? And you disabled it (but forgot to mention doing so in this story) around the same time as swapping routers?

[neon5077]

Nope! Only WiFi and Ethernet. I had been using my phone hotspot, but that gives me a sane IP in the local reserved block, not one from the public block.

I also was using our neighboring business's guest WiFi, but again that should have given me a sane local IP.

Every diagnostic I could think of told me I was directly connected to the WAN with no intervening networks. Then again I'm not the best at debugging networks so I could be mistaken on this point. I am 100% certain that the IP address my computer was given was not a legal local network address.

[hunter2_]

Very interesting! Some kind of buggy DMZ type of thing, perhaps, where even the DHCP traffic flowed right on through... who knows.

[neon5077]

That's about the only thing that makes any sense. Maybe it somehow faulted to route all traffic straight to the ONT, which could only give one address which I happened to get. And then the fiber got cut the very next day around the same time as we got the new router.

A lot of coincidences and extraordinary edge cases, but it's plausible I guess?

[jffhn]

Here is mine.

The admins could connect to their machines, but not to any user machine.

It was winter and we had some heating issues, so I made a script "warmup_the_office.sh" that was meant to launch a "while(true){}" on each core of each PC of the office, but instead launched itself indefinitely on each and all reachable machines, exhausting all pids and preventing distant logging. We had to reboot everything by hand, after some nice warmup.

[neon5077]

What a gloriously dumb idea. If I had that sort of access, I'd probably try something similar, and probably get the same results.

Did you admit what happened, or was there a "mysterious widespread network failure"?

[jffhn]

The mystery didn't last long, and no problem to admit it, I maybe even contacted them. I guess they put safeguards after that, but I didn't try again to check ;)