[privong]

Thanks, but the articles you link don't really describe what I was asking about (and the "TL;DR" doesn't appear to be actually derived from those in an obvious way). I know about the strata and the use of GPS as stratum 0 clocks.

I was interested in more details about why GPS is dangerous (i.e., more about "breaking GPS"). I get that a cheap jamming attack can disrupt a single NTP server/location. But it isn't obvious that that leads to widespread use of GPS being a bad thing for NTP pools. Because it would require a widespread (near-simultaneous?) jamming for several hundred physical locations to bring down a large chunk of the pool in that way. Of course, somehow corrupting the global GPS signal would be an issue, but how would that happen?