> I said top-level domain.

"io" and "com" are top-level domains, and in the example I gave, you can't even distinguish between them.

Well, I appreciate the correction: I meant second level (or whatever is most distinguishing for that TLD). However, even if what you say is true, you really cannot disprove my claim with one nitpick, you need to talk majorities. (And, in case it needs to be said: i really don't think the issue here is distinguishing activity to github.io vs github.com)

Okay, how about this then. Here's some of the IP addresses of posts on the HN front page right now:

  104.21.3.245
  104.21.68.247
  104.21.80.31
  104.21.95.131
  104.21.112.1
  104.26.4.133

None of them have reverse DNS records. Can you tell which is which?

So you take literally the worst possible set of IPs (all of them cloudflare), IPv4 only, and yet Copilot (!) is easily able to reverse 50% of them:

  104.21.3.245 -- trebaol.com
  104.21.80.31 -- diwank.space
  104.26.4.133 -- daringfireball.net 
  104.21.112.1 -- simonwillison.net , taras.glek.net

This was literally the worst example you could possibly do. I hope you kept which one was which, I'd like to know if Copilot was right.

In the meanwhile, from the current top #30 articles on HN (also via copilot script, but I removed non-cloudflare IPs):

  ycombinator.com -- no CDN
  letsbend.de -- no CDN
  grepular.com -- no CDN
  xania.org -- cloudfront
  github.io -- no common CDN
  owlposting.com -- AWS, but IPv4 remained static
  netfort.gr.jp -- no CDN
  simonwillison.net -- cloudflare, 104.21.112.1 fixed
  folklore.org -- azure, 13.107.246.1-255 range
  danq.me -- no CDN
  nature.com -- fastly, IPv4 remained static
  daringfireball.net -- cloudflare, 104.26.4.133
  ssp.sh -- no CDN
  trebaol.com -- cloudflare, 104.21.3.245
  glek.net -- cloudflare, 104.21.112.1
  gov.uk -- AWS, but IPV4 remained static
  phys.org -- no CDN
  diwank.space -- cloudflare, 104.21.80.31 
  free.fr -- no CDN   (my French ISP, btw)
  ericgardner.info -- AWS, but IPv4 remained static
  ghuntley.com -- fastly, IPv4 remained static
  paavo.com -- no CDN
  railway.com -- cloudflare, 104.18.24.53
  alloc.dev -- cloudflare , 188.114.96.2

Look at how many of them are self-hosted, have zero CDN, or otherwise return me always the same IP (even when I try from 3 different ISPs) which makes them trivial to reverse address. This is already a pretty huge success rate and all my context is that you browsed HN first (which I know, see first result on the list). Now imagine the tools a ISP will have at its disposal:

- IPv6

- Its Geo region will actually match yours

- Routing tables

- The patience to also include resources fetched from these pages in the analysis (i.e. page X always gets its JS from Y domain which results in a constant Z KB transfer).

- The rest of your browsing activity

- The rest of everyone's browsing activity including most popular _current_ hosts for each hostname.

Do you still claim that it is "impossible" to track your activity because of CDNs? I still bet you your ISP can do it with _100%_ accuracy.

They're not all running single IP ECH yet. I was just making the point that it's not as trivial as a reverse DNS lookup, as you said it was.

It took me the whole of one Copilot conversation to do the entire thing. Most of the top #30 results are in fact one reverse DNS away. The rest is not much more complicated.

They're never going to be "1 IP ECH" . That would be the end of the Internet as we know it.

If it ever happens that the majority of the WWW is 1 CDN, we have a bigger privacy problem than DNS. Much bigger.