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There is a problem with resolving DNS in my OS X Yosemite.

Safari doesn't load web sites, ping says "unknown host" to google.com. DNS servers set to 8.8.8.8 and 8.8.4.4.

dig google.com

Gets proper information about google.com domain and others. nslookup also works properly.

I cannot reboot because I've got another user logged in and his data will be lost.

Restarting discoveryd doesn't seem to help. TCP dump shows no UDP activity when Safari or ping trying to resolve.

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I experienced that problem on my MBP as well. I suppose it's a bug in Yosemite. Here's a related question: Yosemite cannot resolve domain names maybe it gives you some insight

My work around is flushing the DNS cache:

sudo discoveryutil mdnsflushcache

if that command doesn't work try this one instead:

sudo discoveryutil udnsflushcaches

I am not sure if this helped fixing it, but I did a PRAM and SMC reset as well.

  • Udnsflushcache seem to be taking too much time. It hangs for a few minutes already and no effect from mdnsflushcache. Is there a way to make Safari work via the same DNS as gig or nslookup? – Alexey Shatygin Nov 28 '14 at 9:06
  • I don't have a mac nearby and it's awhile ago since I had those problems but if I remember it correctly, discoveryd is the daemon replacing mDNSResponder so restarting the daemon should help. Did you restart it via load/unload (see linked question in my answer)? – vkvau Nov 28 '14 at 9:12
  • Yes, I used load/unload. – Alexey Shatygin Nov 28 '14 at 9:15
  • Do it again but this time load/unload discoveryd_helper as well. If all things fail, maybe that could help you outdated apple kb – vkvau Nov 28 '14 at 9:23
  • Sorry, did not try restarting discoveryd_helper, but the reboot helped me that time. Thanks anyway. – Alexey Shatygin Dec 6 '14 at 7:07
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If you haven't stumbled on this already, try arp -ad. I don't know why it works for me, but it does. I'm still working on it

  • This worked for me when even rebooting wouldn't work. Thanks! – Learn OpenGL ES Sep 17 '16 at 0:46

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