DNS at exit should tolerate broken providers (aka "Earthlink")
Some ISPs have decided that implementing the internet correctly is not so worthwhile as pointing people towards their advertising. Sadly, some Tor exit server operators have signed up for these ISPs, and every time they attempt to resolve a nonexistant DNS entry, they get the IP for the ISP's "oops! let's help you out!" site rather than the correct error code.
Exit nodes could detect this pretty easily by periodically attempting to lookup a few guaranteed-to-be-nonexistant domains, and seeing whether they resolve to anything. If they do, the exit node could a) switch to using the root nameservers b) treat any IP returned by such test resolves as equivalent to a "no such domain" error. c) warn the operator d) ... ?
[Automatically added by flyspray2trac: Operating System: All]