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Okay, this is a strange one.

Ever since 2017 rolled around I have had this weird situation where I cannot load any pages from an Apple server on one of my iMacs. The strange things about this are:

  • It happens using either Safari or Firefox - but Google Chrome works fine
  • The iTunes Store, Mac App Store, etc are also affected
  • Every other device on the same network (e.g. iPhones, iPads, MacBook Pros, Apple TV, PCs, etc) all connect fine to these servers (including the same Safari/Firefox browser versions running within macOS on a virtual machine on the same iMac)
  • The problem persists regardless of how I connect this particular iMac to a network (i.e. ethernet or Wi-Fi, directly or via a router)
  • All other web servers (as far as I can tell) load fine

Restarting the iMac has no effect, neither does using Safe Mode. Nor did clearing caches, switching off extensions, switching to another user account. I also checked Google Chrome's settings (looking for some sort of DNS caching/prefetching option) to see if I could identify why it works, thinking that would help me troubleshoot the issue - but I didn't see anything obvious.

However, one solution I have found that resolves this issue is:

  • connect using a VPN that places me in another country
  • load apple.com in Safari
  • disconnect from the VPN
  • now all apple servers load fine in Safari and Firefox, as well as both the iTunes and App Store apps

Unfortunately, within a day or so the problem reappears and again, the only fix I've found is the one above. While this fix only takes about a minute, it is nevertheless frustrating, especially when you're in the middle of a workflow and have to access Apple's servers all the time!

Does anyone have any ideas about this?

Remember: This affects Safari, FireFox, iTunes and the App Store apps but not Google Chrome? And only those apps on one iMac are affected, but not within macOS on a virtual machine on the same iMac.

SPECS

The iMac in question has the following specs:

  • 21.5" Mid-2010
  • 16GB RAM
  • Mac OS X El Capitan 10.11.6
  • Safari 10.1 (but since v10.0.2)
  • FireFox 52.0.2 (but since v50.1.0)
  • iTunes 12.6.0.100 (but since v12.5.4.42)
  • App Store 2.1
  • No I don't, but that's a good idea! I hadn't even thought of installing Wireshark to help troubleshoot this. Will do that now! :) – Monomeeth Apr 17 '17 at 23:50
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    IMHO this is clearly related to some DNS/DNS cache/mDNSResponder issue. In your case Google Chrome probably uses it's own DNS client and isn't affected. Please check chrome://net-internals/#dns and the state of the "Internal DNS client". – klanomath Apr 18 '17 at 0:35
  • Thanks @klanomath - I'd previously checked Chrome's settings but couldn't find any relevant DNS info to see if it was using Google's own DNS servers etc. But this is a great tip - I'm not a big Chrome user so didn't know you could use chrome:// in the address bar to access other info (besides chrome://settings). I see that the internal DNS client enabled is flagged as true, so that confirms my suspicions. Thanks for the tip! :) As an aside, is there a way to change this flag to false for troubleshooting purposes? I checked chrome://flags but couldn't find anything. – Monomeeth Apr 18 '17 at 1:10
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    The DNS-async flag was removed. I would draw on LittleSnitch and disable Google Chrome's access to TCP/UDP port 53. Checking my Little Snitch network monitor Chrome accesses the locally configured DNS server(s) and 208.67.220.220 (relation: 1:300 in favor of the Google DNS server) – klanomath Apr 18 '17 at 1:45
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I would be tempted to do two things to troubleshoot this:

  1. Get a new network connection - use a VPN to connect elsewhere or move the computer to an entirely new network.
  2. Install macOS on an external drive and when you have this problem, power off the main macOS and boot to the alternative OS to test in rapid succession if this could be some odd corruption on the os.

You’ve ruled out all the big, easy targets, so this is likely to be something that’s a real edge case or wacky one-off issue. The VM connecting to the network when the host OS cannot is just baffling to me as well.

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