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I'm trying to connect from iMac mid 2010 (10.8.3) to my MBA 2011 (10.8.3) using the Share Screen button in Finder.

I'm able to connect, but unfortunately the connection is closed in a minute and it's not possible to reconnect.

My MBA is behind Airport Extreme and my iMac is behind some 3rd party router.

Interesting that while I'm unable to connect to MBA, I can still mount the disk connected to the Airport.

How can I fix that?

EDIT

It appears that issue is only reproducible when clamshell of MBA is closed and system is asleep. That is, "Share Screen" works just fine if I ask someone to open clamshell and wake up the system. But if clamshell is closed, the issue I described above is always reproducible.

A little bit of info: I have File Vault enabled on MBA.

  • If you connect them both to the same router, does it work? – Undo Jun 3 '13 at 14:42
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I am missing one critical detail in your description: How are you connecting?

  1. VPN
  2. iCloud / Back-to-my-Mac
  3. LAN

Meanwhile - assuming it's either 1. or 2 - these are the quick check's I would perform initially and one-at-a-time.

  1. Check if it works the other way around: MBA -> iMac
  2. If you connect via VPN, try Back-to-my-Mac instead
  3. Make sure all routers run with current firmware
  4. Both routers should have UPnP (non-Apple) and NAT-PMP (Apple) enabled. Some 3rd party routers allow more fine-tuning with UPnP. While this basically opens up your network (and makes it more insecure), I would go and open up for now, just to see if this solves the problem.
  5. (temporarily) disable your firewall on both Macs. If you are running any 3rd party firewall app (such as LittleSnitch), switch if off for now.

Glad to hear if any of this opened your door again.

  • iCloud / Back-to-my-Mac. The problem is that connection is made for the first time. I could understand if it didn't work at all, but not that. – Kentzo Jun 3 '13 at 16:05
  • Do you have the same problem the other way around? Try to connect from MBA -> iMac. – OvQ Jun 8 '13 at 14:16
  • Yes it works smooth. – Kentzo Jun 8 '13 at 23:09
  • Turn off Back to my Mac on your iMac. Additionally, turn of anything in the sharing preference pane. Then restart your iMac and turn everything back on. – OvQ Jun 8 '13 at 23:36
  • sorry, didn't help. Please see update to the question. – Kentzo Jun 16 '13 at 17:34
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You are correct in that it only works when the clamshell on the MBA is open. When it is closed, the computer goes into sleep, turns off all network connections, etc.

To remedy this, you can install NoSleep, a little menubar app that should allow you to keep the computer from sleeping even when it is closed.

  • My MBA is behind Airport Extreme which supports Bonjour Sleep Proxy which in turn WAS able to wake up iMac (when it was there). It's actually able to wake up MBA, but for short time. After a minute or so it goes to sleep again. I hope it's something that can be fixed. – Kentzo Jun 18 '13 at 8:06
  • @Kentzo: I would still try NoSleep or a similar app and see if that solves it. – ZuluDeltaNiner Jun 18 '13 at 14:00
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Since file sharing works and screen sharing does not, the pragmatic solution is to establish a file share to keep the clamshell mac awake and then share the screen.

Since screen sharing operates on a different internet port than file sharing, this would be a router/firewall issue where the file sharing traffic is being treated differently than the screen sharing traffic.

In the end, if your Mac is closed clamshell, the OS will sleep the machine unless you meet all the requirements for your particular SMC.

Once you've sorted the OS lid sleep triggering issue, you can use many programs to keep the OS running like Caffeine or Screens Connect. The latter is great free software that I use in addition to Back to My Mac when I really need to get back to a specific Mac since each does part of the chain best and having two location (and remote wake) methods is in this case better than one. I use ssh as the second remote-wake mechanism rather than file sharing, fwiw.

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