[TChris]

Everything else will just route around the break. It might be slower because overall capacity has been reduced, but it doesn't isolate them.

That's the way it's SUPPOSED to work.

But it's far cheaper to have NO redundancy or only pseudo-redundancy (redundant circuits in the same conduit, for example) and there are plenty of places on the 'net where that is the case.

[justlurking]

But it's far cheaper to have NO redundancy or only pseudo-redundancy (redundant circuits in the same conduit, for example) and there are plenty of places on the 'net where that is the case.

As I posted moments ago, there are definitely cases where this occurs. But, it's the fault of providers that have limited peering agreements.

There used to be a backbone diagram of the 'Net in the US, along with its connections overseas. There is plenty of physical diversity in the routing. The problem is if your particular ISP limits which ones it uses.