Browser DNS caching

The curious question of DNS caching in web browsers.

This has been a problem since the early days of the web: browsers (IE, Mozilla, etc) which do their own DNS caching, regardless of what the host platform's DNS resolver is doing. It's documented:

• Simplefailover.com documents it in IE and Firefox/Mozilla-based browsers. 
• Microsoft's KB263558 shows how it works in all IE versions. It seems to say that IE does its own DNS lookups completely independent of the DNS resolver, but a simple test shows that the local DNS client is still in the loop. Run ipconfig /flushdns, then browse to any site in IE, then run ipconfig /displaydns  ... that site's DNS name and IP are added to the local DNS client cache.

Of course the problem here is that while documented, it's not known to many network practicioners. Even those who know about this mechanism curse it, because it is impossible to manually peer into. System admins, network admins, etc, depend on the ipconfig /flushdns and ipconfig /displaydns utilities to troubleshoot typical user "I cannot reach the website" issues. These utilities allow troubleshooters to manually inspect and clear the DNS cache. Because the web browser cache cannot be accessed in this way by the troubleshooter, he cannot know for sure that improper DNS caching by the browser is (or is not) the culprit. Nor can he see which address has been cached by the browser, as a way of tracing the problem back to its root cause.