In London I can literally follow the map from manhole to manhole, exchange to exchange. It's dark fibre so I can flash a light down it and a colleague can see i

In London I can literally follow the map from manhole to manhole, exchange to exchange. It's dark fibre so I can flash a light down it and a colleague can see it emerge at the other end. Now it's possible they don't follow the map and still make it to the other end, but it's pretty unlikely. Sometimes of course you have to make judgement calls. From one location near Slough I have a BT EAD2 back to my building a few miles away. I know the route into my building, I can see the cables with my own eyes going in different directions. BT tell me which exchanges those cables goto, and provide me with a map into the field at a 1000:1 scale showing the cables coming in down a shared path. Sure it's possible BT are lying, but it's unlikely. Only use that location sporadically, and when I do it's a managed location, so I can accept the risk of a digger on the ground. Another location in Norfolk, two BTNet lines, going to two different exchanges. They meet at the edge of the farm and go up the same trunk. That's fine, I can physically control the single point of failure there too, although if peering between BT and my network fails then I'm screwed, but I have a separate pinnacom circuit in a crunch. Now obviously some failure become far harder to mitigate. A failure of the Thames Barrier would cause a hell of a lot of problems in Docklands, I'm not sure if any circuits in/out of places like telehouse, sovhouse, etc will remain. Cross that bridge etc. Whether my electricity provider will remain with a loss of the internet is another matter, so then it comes down to how much oil there in in the generators, and the generators of any repeaters on the routes of my network. However the much easier to avoid is the problem of some shitty stacked switch the salesman says will always work.