Mac Screen Sharing Problem

[TalosLS]

It seems odd to be reporting a screen sharing problem between two Macs here, but I am now at the point where the only common denominator is my new Bell Giga Hub router.

I have a Mac Studio (M1) and a MacBook Pro (Intel).  I use the Mac Studio in headless mode, controlling it from the MBP via either Mac Screen Sharing or via NoMachine.  I have done this since the Mac Studio was new, and prior to that with a succession of Mac Minis that preceeded it.  I have not had any problems whatsoever.  Until now.

I recently moved house, and following the move Bell installed a Giga Hub modem/router.  Prior to that I had a Bell Home 3000 (or something along those lines).  After the technician finished installing the system, I was immediately able to use Screen Sharing to operate the Mac Studio.  However, the following day Screen Sharing refused to connect to the Mac Studio.  I had done absolutely nothing to the system in the interim.  Nada.  Both computers were still connected to the network, and could access all the other available network resources just fine.  Just not Screen Share.

Over the coming weeks I tried everything under the sun to troubleshoot this problem, but with no success.  My MacBook Pro cannot connect a Screen Sharing session with the Mac Studio.  In fact, it cannot even connect a file sharing session.  The error message is along the lines of "the remote computer cannot be found on the network".  I have disabled the FireWall and checked, double-checked, and triple-checked every mildly relevant setting on both Macs.  Everything, including the Bell Giga Hub has been cold booted several times and in several different sequences.  All is as it (supposedly) should be.

This week the new Sonoma version of macOS was released, and so I simultaneously upgraded both the MacBook Pro and the Mac Studio to Sonoma.  On first boot-up, I was immediately able to initiate a Screen Sharing session, which worked flawlessly for the rest of the day and evening.  I figured that the Sonoma upgrade must have fixed whatever it was.  But then the following morning it would not connect again, and I am right back to where I was before.  I have spent the last two days going up and down, backwards and forwards, through all the usual suspects, and it is clear that the problem has gone right back to square one.

So I have no choice but to conclude that the only remaining common factor is the Bell Giga Hub router, although I am at a loss to explain what it might be doing wrong.  It doesn't seem to have the tools to check whether any of the necessary Ports (Mac Screen Sharing uses Port 5900) are being blocked.  All my tech expert friends are as baffled as I am.  So I could really, really do with your help here 🙂

[ZaneP]

Hi @TalosLS 

"All my tech expert friends are as baffled as I am"

If your tech experts can't solve this, I'm not sure how much help I can be!

I'd be surprised that the Bell Hub is playing a role in the problem, but I think you need to use the modem's portal to look for issues.

When you see that error message - "the remote computer cannot be found on the network" you should log into the modem, go to My Devices, and see if both devices have a LAN  connectIon. What you're describing indicates to me that one of the Macs isn't connected. Also have a look on each Mac's network settings to ensure the IP address is correct. The Giga Hub's DHCP server will be assigning the addresses, as I'm sure you know.

I assume you checked this (from a Mac support doc):

"Make sure both computers are connected to the same network.

• To check your connection, choose Apple menu > System Settings, then click Network in the sidebar (you may need to scroll down). On the right, the indicator next to your type of network connection should be green. For a Wi-Fi connection, click Wi-Fi to check the network name."

I also assume that after the OS update to Sonoma you looked at all relevant permissions settings in System Settings on both.

Are both Macs connected via ethernet, or ethernet for one, wifi for the other, or both wifi?

The modem can do port-forwarding for inbound traffic and has the tools for it, but the port you mentioned shouldn't be blocked at all for internal traffic.

Hopefully others in the forum who use Mac screen-sharing will contribute to a solution.

Keep us updated.

Cheers,

ZaneP

[TalosLS]

Thanks, Zane.  As you surmised, I have already checked all these possibilities.  Both computers are connected to the same network (via the same Wi-Fi SSID).  The Giga Hub portal sees both of them, and reports the same IP addresses that the computers themselves report.  Both computers can connect simultaneously to the other shared resources on the network (including 2 NAS units and a printer).  I did meticulously check all of Sonoma's permission settings, although I can't entirely eliminate the possibility that there is a permission that has to be granted that I am unaware needs to be granted.  I should point out, though, that (i) everything worked fine for the first day after upgrading to Sonoma, and failed the subsequent day without my having changed a single thing; and (ii) the problem was there for several weeks prior to the Sonoma upgrade, and was not there for the first day after Giga Hub was first installed.  In fact, this odd behaviour seems strangely consistent:  I make a major change to the system and my Screen Sharing connection works thereafter for the first day, only to fail permanently on subsequent days, until the next major change.

I am really baffled as to what to do next, but remain convinced (without any smoking gun to prove it) that the problem lies in the network/router rather than in the Macs themselves.

Thanks,

RichardM

[ZaneP]

Hi @TalosLS

Given everything you described and what you've done to solve this, I'm at a loss on further steps. However, to explore if the Giga is the issue, some thoughts:

1. This is a stretch, but maybe having the latest modem firmware resolves the problem. The latest is 1.19.5.1. You could try a factory reset to get this version. But you'll lose any custom settings, so make notes.
2. When this problem occurs, go into the modem dashboard, Advanced Tools and Settings. Then select System Logs, select Error and Warning messages. See if the modem is reporting any errors before screen-sharing failed.
3. Ask Bell for a replacement modem, which would help determine if there's any problems with the one you have. It's unlikely, but could be worth it.
4. Another stretch: are there any other software tools for screen-sharing you could use, like VNC? Or is the Mac OS already using it as part of the built-in app?
5. Ask your tech friends if it would be useful to attach a third-party router to the modem, and turn off the Giga's routing. This is a long-shot, it adds costs, and can introduce other issues since there's no true bridge-mode connection. But if screen-sharing is mission-critical it's worth asking.

You could also post this issue on the Bell forum at DSL Reports. There may be some help there. https://www.dslreports.com/forum/sympat

As well, it may be worthwhile to post on the Bell Reddit. https://www.reddit.com/r/bell/

Let us know how it's going.

ZaneP

[TalosLS]

Thanks again Zane - great points.

1. I checked the firmware, and it is indeed 1.19.5.1
2. The system logs contain no entries at times when I try unsuccessfully to connect.  But in general, I have seen no entries suggestive of a problem happening somewhere; although I need to look deeper into this aspect.
3. That's possibility, although I think I would need to be able to make a more convincing case that a defective modem is the problem.
4. I do have other options for Screen Sharing, but none of them work either.  In fact, as far as I can see, I am failing to make *any* network connections with the Mac Studio.  That is, except for the fact that the Mac Studio does show up in Finder's list of Network Locations.  So bizarre.
5. Sadly, I have recently moved to a more rural location, and all my neighbours (at least those I have met so far) are also retired.  No sigh of any tech wizardry thus far .... 🙂  My first stab at this is going to be to see if anyone in the neighbourhood has a Mac laptop, and if they are willing to come round and see how they get on connecting to either my Mac Studio or my MacBook Pro.

For sure, I'll post an update here if and when there is one 🙂

RichardM

[ZaneP]

Hi Richard,

Good idea to see if another Apple device can connect.

I'm also rethinking the ports issue...an even bigger stretch (!) but might be worth another look, just to confirm that port 5900 isn't blocked . There's a good internal port scanner - nmap - which can be run from Terminal. If you have Homebrew on your MBP, just run "brew install nmap". I've used it on my MB Air.

more here: https://www.maketecheasier.com/scan-local-network-with-terminal-macos/

Anyway, I hope you get this issue resolved, and soon!

All the best.

[TalosLS · Accepted solution]

I finally got to the root of this problem, so I thought I'd post the answer here.

It turns out that the problem is due to having VPN software installed.  Apparently this interferes with Apple's 'network discovery' protocol, resulting in the remote device not being 'discovered'.  But the solution, apparently, is not just to make sure the VPN isn't running ... you actually have to *uninstall* the software.  In my case, the VPN software was VyprVPN, but Apple told me that it doesn't matter whose VPN software it is.

Bottom line ... the software is uninstalled and the problem has (apparently) gone away.  Having said that, I'm not 100% convinced by Apple's explanation.  They've clearly broken something somewhere and aren't fully owning up to it.  This, unfortunately, is standard practice for Apple.  Anyway, over the coming weeks I'm going to dig deeper into this, but I won't necessarily post any further findings here.

[Vanadiel]

That would make sense as the VPN service will tunnel to the VPN network, and unless you can configure it for whatever protocol Apple uses to connect remotely, it will not work. Same would be true for Microsoft remote desktop.

[TalosLS]

Well yes, on the face of it.  But it has worked perfectly for almost 10 years, through several iterations of hardware and OS, and only just failed somewhere along the Ventura timeline.