August 10, 2026

Anycast breaks IP geolocation — and that is fine

Anycast IP geolocation is a category error. The address is in several metros on purpose. A vendor that prints one city is picking a pop they like, a registry they cached, or the location of the covering prefix’s NOC. None of those is “where the packet went.”

I confirm anycast the cheap way: IPv4 and IPv6 ping from more than one continent. If latency is local everywhere, you are not looking at a single basement. Then I open the looking glass. Different collectors, different next hops, same prefix — that is the shape. The IP geolocation table will still argue. Let it.

How to write anycast IP geolocation without lying

I write “anycast, pops in at least X regions” or “single-origin, geo disagrees.” I do not write “the user is in Dallas” because a CDN node is in Dallas. Country can still be useful for licensed content. City is a slide decoration. Category still matters: cloud vs residential does not suddenly become honest because the logo is a CDN.

If min RTT is 8 ms from Frankfurt and 9 ms from Virginia, stop decorating maps.

When geo is still worth running

On unicast space, geo plus origin from an IP lookup is how I sort a flood. On anycast, I sort on ASN and prefix, not city. Publish a geofeed if you announce anycast and you are tired of vendors inventing a headquarters — RFC 8805 is the adult version of that conversation.

Anycast is not a bug in geolocation. Geolocation is a bug in how we talk about anycast. Use ping, use the glass, then put the pin away.