[seszett]

They don't have to assume that traffic is efficiently routed, on the contrary if they can have a <1ms RTT from London to a server, the speed of light guarantees that that server is not in Mauritius EVEN if the traffic was efficiently routed.

It just can't be outside England, just one 0.4ms RTT as seen here is enough to be certain that the server is less then 120 km away from London (or wherever their probe was, they don't actually say, just the UK).

RTT from a known vantage point gives an absolute maximum distance, and if that maximum distance is too short then that absolutely is enough to ascertain that a server is not in the country it claims to be.

[preinheimer]

We've got detailed global ping data here: https://wondernetwork.com/pings

One of our competitors was claiming a server in a middle eastern country we could not find any hosting in. So I figured out what that server's hostname was to do a little digging. It was >1ms away from my server in Germany.

[ramity]

I see I was mistaken, but I'm tempted to continue poking holes. Trying a different angle, though it may be a stretch, but could a caching layer within the VPN provider cause these sort of "too fast" RTTs?

Let's say you're a global VPN provider and you want to reduce as much traffic as possible. A user accesses the entry point of your service to access a website that's blocked in their country. For the benefit of this thought experiment, let's say the content is static/easily cacheable or because the user is testing multiple times, that dynamic content becomes cached. Could this play into the results presented in this article? Again, I know I'm moving goalposts here, but I'm just trying to be critical of how the author arrived at their conclusion.

[seszett]

This is about ping though, so presumably ICMP packets. There is no content to cache as the request is sent with random data that must be sent back in the reply.

It is very unlikely that VPN providers use convoluted caching systems just to make their ping replies appear to come from a different region than the one they claim to be in. It would be much more likely for them to add a little latency to their responses to make them more plausible, instead.

[ghxst]

Assuming a secure connection this isn't possible without terminating TLS and re-negotiating.