I spent more time than I care to admit doing dual-stack IP detection in a way that works on modern browsers and all the way back to Internet Explorer 6.

I learned that IE6 will refuse to do XHR unless the host+port are identical to the current URL, and it doesn't support CORS. So, the workaround was using JSONP.

I wonder how many other people in the world have IE6 running with IPv6 support...

#ipv6 #internetexplorer #windowsxp