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Screen Sharing stops working when using separate networks

I'm having an issue accessing my work iMac from my MacBook at home. I've enabled Remote Management and Remote Login (along with every other Sharing option) through my System Preferences on my iMac at work.


To test the connection, I used my MB on the same network and successfully used the Screen Sharing app. But when I got home and tried to connect I got a "Connection Failed" error. Remote login through Terminal also timed out.


I made sure my iMac doesn't sleep, although the display goes to sleep after some time. I also successfully connected to a local computer also using Screen Sharing, so I know it's not my network. I'm connecting using "vnc://ip.address," and I've also tried adding port numbers. The work iMac's IP address is static, so the address couldn't have been renewed.


Any suggestions for this issue?

OS X Mountain Lion (10.8.1)

Posted on Dec 5, 2013 7:05 PM

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10 replies

Dec 6, 2013 6:43 AM in response to sylekimmonds

If there is a router at work, then unless your work Mac is using something like Back-to-My-Mac, you will never see it, as the work router will block all access.


NOTE: You do not need "Remote Management" enabled. Just "Screen Sharing". Remote Management is if you have purchased the Apple Remote Desktop package, which is intended to manage a class room full of Macs, not remotely connect to a single Mac. Screen Sharing is what you use for what you are doing.


Remote Login is used for SSH connections (Secure SHell terminal sessions). If you are not using the Terminal to connect to your Mac, or a utility that sets up SSH tunnels, then you do not need "Remote Login" enabled.


If you cannot get Back-to-My-Mac working, then you might want to look at TeamViewer.com, as their remote screen sharing package can generally get through any home router.


NOTE: If work is using a Corporate Firewall and Proxy servers to access the web, then TeamViewer.com can work though a Proxy server, as long as the corporate proxy server do not block the TeamViewer.com servers.


If the work router is your own (as in you are a small business and in charge of the router), then you could also try configuring the router to allow Back-to-My-Mac (BTMM). If you do not want to allow BTMM, then you could look at setting up Port Forwarding <http://portforward.com>

Dec 6, 2013 7:24 AM in response to Linc Davis

Bob, thank you for the response. I was using SSH initially and used it to test the connection when Screen Sharing stopped working. I also tested both Screen Sharing and Remote Management, but I'll revert to Screen Sharing when I'm able since I only need to access the one computer.


With using ports, some resources I found online said to use ports 5900 and 59001 for VNC. If I was to use Screen Sharing instead of Back to My Mac, do I still need to forward ports?


Linc, in regards to the VPN connection, if I had the login credentials to access the network, would the VPN allow Back to My Mac or Screen Sharing access (or both)?

Dec 6, 2013 7:40 AM in response to sylekimmonds

Are you a small business and in control of the work router?


Or is this a corporate network, and you are just one of the employees?


If a corporate network, then a VPN connection is typically how those of us working for large corporations gain access to the work network from home. Corporate IT provides the connection software, the VPN accounts, etc...


Generally, if you can access work via the corporate VPN servers, then it is possible to do Screen Sharing over the VPN connection, as corporate VPNs tend to make your home system part of the corporate network. I was just doing this last night from my living room.


However, if you are a small business and in control of your own network, then you get to either configure the work router to allow Back-to-My-Mac, or configure the work router to port forward port 5900 (the VNC/Screen Sharing port number) from the router to your work Mac, or try using TeamViewer.com (there are lots of other options with different levels of complexity). TeamViewer.com would be my first choice if you do not want to mess with your work router at all, or as a starting point that you can expand as you have time to explore.

Dec 6, 2013 9:00 AM in response to BobHarris

Linc and Bob, thank you for the suggestions. I'll try to get the credentials and see if it works. In the meantime, it would be helpful to know if this is being caused by my own router or the network at work. I've successfully connected to other computers locally on both networks, so I can't tell where the issue is.


Bob, I checked out TeamViewer and will try it if this doesn't work, but shouldn't I be able to connect without using third-party software? It seems like the Screen Sharing app isn't the issue, but rather the network.

Dec 6, 2013 10:31 AM in response to sylekimmonds

in the meantime, it would be helpful to know if this is being caused by my own router or the network at work.

The destination router. In your case the router(s) at work.


Bob, I checked out TeamViewer and will try it if this doesn't work, but shouldn't I be able to connect without using third-party software? It seems like the Screen Sharing app isn't the issue, but rather the network.

Yes it is the work network that is in your way.


Home routers and especially corporate routers block unsolicited connections from the internet because there are bad things happening out there.


Back-to-My-Mac sets up its own connection port through your home router to the internet along with connection security to allow you to connect from outside your home (unless the UPnP or similar services are disabled).


Corporate networks do not allow employees to open ports in their networks, which is why they frequently require the use of a Proxy server to surf the web and VPN connections to allow employees to connect from home. In a way, Back-to-My-Mac acts like a VPN for home users going Mac-to-Mac. But corporations are not going to allow Back-to-My-Mac through their firewalls.

Screen Sharing stops working when using separate networks

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