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BACKGROUND:

I have an iMac in my office which is connected to the eduroam network (which is a common network in universities). When I am not in the office, I can use the Apple's application Screen Sharing to connect to the iMac through my MacBook Pro.
In the "Sharing" panel of the iMac settings I have just "Screen Sharing" selected, and I allow just administrators to connect. Then, I just have to copy the vnc string I find in the same folder inside the Screen Sharing application, insert the credentials of the iMac, and it works.
You can have a look at the Sharing panel in my settings. It's from here that I get the vnc path to connect to the iMac.

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THE PROBLEM:

I have another laptop, a MacBook Air, that is at home, connected to my personal router. If I am on a different network, always with my MacBook Pro, and I try to use Screen Sharing in the same way to connect to the MacBook Air, it doesn't work. For this second computer, the Screen Sharing App works only if I am on the same network of the MacBook Air.

QUESTIONS:

  1. Does anyone know what are the difference between the two computers and why I can connect to the iMac and not to the MacBook Air? Thanks in advance for your help!

  2. In case it's not possible to do that through the use of the vnc, maybe it can be done by specifying the Apple ID, but in that case someone on the other side should accept my request to control the screen. Is there a way to do it automatically?

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  • I'm no Sharing expert… but where did you find this 'vnc string' & precisely what does it say? You can connect to any remote location without having to drill your way through any router structure [certainly on domestic routers, not sure about corporate] by invoking the AppleID of the remote. idk if you can set that to auto-accept, I've only ever used manual, with the recipient there to click the button.
    – Tetsujin
    Nov 1, 2022 at 9:30
  • Hi and thanks for you comment. I've just updated the Question by adding, at the end of the first paragraph, a link to the screenshot of my Sharing panel, in Settings. You're right about using the Apple ID, and it should work, but I have no one that "accepts" my request to log-in. There should be a way to do it automatically, right?
    – nd091680
    Nov 1, 2022 at 10:08

2 Answers 2

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Partial answer, to work on. Far too long for comments…

That VNC address will be a local subnet address, 192.168.x.x or maybe 10.x.x.x etc. The address is not valid from outside your network - or more specifically, it's an address not specific to you, personally, but owned by several billion people around the globe, all behind routers too. Your router knows who your are, when you access the outside world using a process known as NAT (Network Address Translation).
One simple aspect of NAT is if you make a connection from inside, it knows who you are & gives permissions liberally. If you try to hack your way in from the outstide… it's not going to let you without some very specific permissions & routing set up just for that one computer.

Your IT department would have to set this up for every user; using one of several [not important to us right now] methods.
This is not going to happen, for obvious reasons.

The advantage of using the Apple ID is it uses the remote computer's existing known presence on the internet. To the end user, this is similar to how such as TeamViewer, LogMeIn, etc work. It uses established connections initiated from inside the network so already has permission to punch through the firewall. The router sees this as an outbound connection & doesn't prevent it, or need to route it in any 'special' way.

I've only ever done this using the Apple ID, which manages to accurately locate my father-in-law half a country away.

Apple's Help page on Screen Sharing doesn't really seem to mention this method. When I do this to remote to my father-in-law's Mac, it's the only Mac with his Apple ID, so that's all I type in the connect to box. He has to be present to allow the connection - I've never seen the connect perms box; maybe there's a permanently allow, idk.
Also, because I'm connecting to an ID other than my own, nothing is going to confuse which Mac I mean. If you're trying to connect to yourself, this is perhaps going to be different.

Without being able to test this myself, I'd suggest trying to do this when you have both computers in the same room, on campus. Tether your 'home' Mac to a phone, so you're using the phone's internet connection, not the local one. This will put you in a random 'foreign' network, allowing you to see & interact with both computers as the connection initiates.

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  • Thanks @Tetsjuin for you detailed answer. I've already tested the two computers in the same room, connecting the MacBook Pro to the data of my mobile. I also agree that the best solution, in this case, would be to use the Apple ID, because it's indeed very specific, but now we need to understand if there is a way to avoid the "Accept" notification. Any ideas?
    – nd091680
    Nov 1, 2022 at 16:00
  • I'm afraid this is the bit I cannot test, sorry. I don't actually use Screen Sharing for anything other than this one remote 'dad's computer management' task & tbh, unless I'm at his house, looking over his shoulder as this happens, I will never get any proper info as to what happens at this point. (ikr? ;) For everything else, I have the full Apple Remote Desktop to admin all the other Macs in the building, which requires simple Screen Sharing to be off; so I can't even poke at the settings, I'm afraid. I had really hoped there would be an option to "always allow" on the receiving Mac.
    – Tetsujin
    Nov 1, 2022 at 16:45
  • I can see from google that there's an option to save credentials when using vnc, but I cannot find any useful info when using Apple ID. Prefs for vnc connections are saved at ~/Library/Application Support/Screen Sharing/name.vncloc but Apple ID connections are not in there, neither can I find any reference in the keychain.
    – Tetsujin
    Nov 1, 2022 at 16:48
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    Thanks again for the answer, I will make a try contacting the Apple Support
    – nd091680
    Nov 2, 2022 at 18:39
  • I wish you luck :))
    – Tetsujin
    Nov 2, 2022 at 18:44
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I don't know if it can be considered a real answer, but I wanted to post it here because in this way it might help someone else who is experiencing my same problem.

From the App Store I bought the application Screens 4 for 29 €. It works like a charm. I can control every computer I want, even if they are on different networks. For iOS it is also available an application to control everything from the iPhone.

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