Tuesday, January 13, 2015 [Tweets] [Favorites]

Why DNS in OS X 10.10 Is Broken

Iljitsch van Beijnum:

For 12 years, the mDNSResponder service managed a surprisingly large part of our Mac’s networking, and it managed this task well. But as of OS X 10.10, the mDNSResponder has been replaced with discoveryd, which does the same thing. Mostly. Here are some strange networking problems we’ve observed since installing 10.10[…]


If discoveryd isn’t doing its job properly, sometimes it helps to restart it. However, even this doesn’t always work, and restarting discoveryd gets old fast. If you’re not scared of a little command line hacking, there’s a better solution: you can reinstall the OS X 10.9 mDNSResponder on a 10.10 system. And after that, all the problems listed above magically go away.

I wouldn’t do that; go back to a full 10.9 system if 10.1 isn’t working for you.

Update (2015-01-13): Paul Horowitz on “How to Flush DNS Cache in OS X Yosemite with discoveryutil”.

Update (2015-03-31): Craig Hockenberry:

Why isn’t there a tech note about all of these DNS issues in Yosemite? Does Apple not care? Or do they not know?

Chris Parker:

It’s known. And the teams care. Don’t know why there isn’t a reunite though.

Craig Hockenberry:

There are A LOT of people burning A LOT of cycles on this stuff. Communication would go a long way…

Update (2017-07-14): See also: Accidental Tech Podcast.


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[…] Previously: discoveryd Is Still Buggy, Why DNS in OS X 10.10 Is Broken. […]

[…] because of the many PDF bugs, which go way beyond what I’ve documented. It looks to me like a discoveryd-type situation. One developer e-mailed me to […]

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