Going back to the pre-Yosemite DNS service is one way to fix these problems.



From ArsTechnica:

Today, Apple released a new beta build of the OS X 10.10.4 update, and it turns out that Apple's fix for the problem was the same as ours: 9to5Mac reports that the discoveryd service is gone, and it's been replaced by the mDNSResponder service that handled DNS in Mavericks and older versions. That doesn't mean discoveryd is gone for good—Apple could try to fix its bugs and reinstate it in a future update, or it could even be reintroduced in a future OS X 10.10.4 build—but it does appear to be gone for now.

  New OS X beta dumps discoveryd, restores mDNSResponder to fix DNS bugs