macOS 10.12.1 (16B2555) on an early 2015 Macbook Pro.

I can't resolve any .io domains on this machine. Other people on the same network can. This happens here at the office, and at home.

I've tried different browsers, I've turned it off and on again.

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[~]$ nslookup ngrok.io

Non-authoritative answer:
Name:   ngrok.io
Name:   ngrok.io
Name:   ngrok.io

[~]$ ping ngrok.io
ping: cannot resolve ngrok.io: Unknown host

If I add the domain manually to /etc/hosts, and then run a traceroute, I don't see anything abnormal. I'm able to bring up the domain in a browser.

Definitely seems like a DNS issue, however, I'm not using DNS settings that are any different from anyone else on either my home or work network.

If I change the DNS servers manually to, it STILL does not work.

  • When you say "it happens here and at home" I am assuming it's on the same machine (like a MacBook), correct? How do you have your IP setup? Full DHCP or are you making some manual settings?
    – Allan
    Oct 29, 2016 at 0:48
  • DHCP on both networks, same macbook
    – synic
    Oct 29, 2016 at 1:01
  • 1
    Can you flush your DNS; issue the command: sudo dscacheutil -flushcache;sudo killall -HUP mDNSResponder;say cache flushed
    – Allan
    Oct 29, 2016 at 1:07
  • No change at all :(
    – synic
    Oct 29, 2016 at 2:49
  • Looks to be similar to apple.stackexchange.com/questions/24018/… but, I don't know if the same fix would apply to 10.12 or not
    – Kent
    Oct 31, 2016 at 0:53

1 Answer 1


You may have been impacted by recent issues of a portion of the .io TLD Nameservers delivering NXDOMAIN responses which then cascaded throughout all DNS entries globally.

Only a portion of the nameservers were doing this, leading to discrepancies in the cached values downstream, which in turn lead to intermittent failure to lookup the host server when making requests.

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