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Comment by colmmacc | Hacker News Reader

zvanness, would you be interested in also implementing this;

    http://whatsmyresolver.stdlib.net/
    curl -L  http://whatsmyresolver.stdlib.net/resolver/

? It should be relatively easy to add (happy to explain how it works), and I'm personally longing to turn off my service!

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Sorry to intercept, but how does it work?

My first guess would be that the domain uses a custom nameserver that logs all dns queries and serves back a different IP to each user. Then when the http request comes in to that specific IP, it can check the dns logs to identify the resolver.

But surely.. that would either require (a) a massive IP space (i guess that works if the site is IPv6 only), or (b) assuming a pretty short time between dns lookup and http request, and hence possibly false results if the dns lookup is cached somewhere and the IP has since been reused

I'd love to know if there's a better way of implementing this.

A better way would be to hand each client a unique hostname (sessionidhere.whatsmyresolver.stdlib.net) and match that dns query to the http client? For example as an ajax call from the main website.

curl $(</dev/urandom tr -dc a-z|head -c32).mydns.re

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