[coffeeri]

This is/was also my take. I’m skeptical that a probe-based network can be granular enough to reliably pinpoint a city, especially when some paths are much better connected than others (fewer hops, uncongested fiber, no throttling).

However, ipinfo still appears to rely on active probing to triangulate geolocation data, which suggests they believe these routing asymmetries can be modeled or averaged out in practice.

https://ipinfo.io/blog/ipinfos-probe-network

[direwolf20]

I think the idea is that if you have enough probes, one of them will be in the right location and network.

Tier 2 ISPs have the right incentives to peer with every network in every peering point, so you are likely to get a correct result from a different ISP. Tier 1 ISPs avoid peering, so if your probe or target is on Deutsche Telekom or Cogent, your packet takes a circuitous route, passing only through networks that paid the extortion money.

Friends don't let friends get internet service from Deutsche Telekom or Cogent.

[toast0]

It depends on the city, and how the ISPs in the city work.

The telco DSL and fiber in my metro area all runs through a single location where the PPPoE (hiss) concentrator is and the first hop latency from DSL interleaving swamps the latency from distance. You can someone is in the metro area, but not the county or city.

Cable company customers are a little more locatable, probably get the county.