[mdisraeli]

ipconfig /flushdns

The above will manually clear out the windows DNS cache. Note this doesn't block it, but rather simply limits what it can find out. I'm not sure it would be possible to block this functionality entirely without also breaking DNS, or otherwise causing the Anti-cheat tool to detect something odd.

By default, the Windows DNS cache doesn't flush itself, with entries lasting for 24 hours or so. As stated in the post, you can view currently cached domain names by entering

ipconfig /displaydns

Strangely, this doesn't seem to list some of the sites I've visited this morning within firefox

[blueskin_]

Firefox has its own DNS cache - emptying the normal cache in firefox also (silently) clears it.

[pfg]

Are you sure about that?

Here is what I've tried:

  ipconfig /displaydns | grep foobar.com
  #empty
  #open foobar.com in Firefox
  ipconfig /displaydns | grep foobar.com
    foobar.com
    Record Name . . . . . : foobar.com
  #delete firefox cache
  ipconfig /displaydns | grep foobar.com
    foobar.com
    Record Name . . . . . : foobar.com

[Dylan16807]

I think you misunderstood. Emptying the firefox data cache silently clears the firefox dns cache.

[pfg]

At which point the entry would still be cached by the OS, and since firefox apparently uses the OS API to resolve hostnames (if it didn't, I wouldn't have found the entry in my cache after opening the site, right?), it would still return the cached result (as long as it's not expired).

Besides, the question was how to prevent VAC from uploading your (hashed) DNS cache, and clearing Firefox cache doesn't flush those entries from your OS DNS cache.

[Dylan16807]

First off, in that case I'm not sure what your experiment was supposed to demonstrate.

More importantly, Windows will cache DNS records for no longer than the TTL. Firefox will keep entries in its cache for hours if not days. That's how sites you have been visiting will not show up in the OS cache.

[pfg]

OP asks if it's possible to block VAC from leaking your DNS cache (specifically the OS DNS cache obtainable via ipconfig /displaydns).

blueskin_ mentions that Firefox uses its own DNS cache, and deleting the browser cache also deletes the DNS entries.

However Firefox still uses the Windows API for DNS resolution, and deleting the browser cache doesn't result in those entries being flushed from the OS DNS cache (which is demonstrated by my experiment.) In other words, simply deleting your browser cache in Firefox will not prevent VAC from uploading your OS DNS cache. As long as the entries aren't expired or flushed manually, they will remain in your OS cache and VAC has no problem getting them.