Windows 11: Public Network VS Private Network

[ruckb]

Hello,
I have 2 new Windows 11 PCs and originally their network was configured as public network.
At this time I could easily connect from my normal PC (further on called host is in the same network inside my house) without issues with UltraVNC 1.4.3.6.

Then I changed network of the new PCs to a private network, but for both I got the message "Failed to connect to server!"
Switching back to public network VNC connection works again...
The two new PCs are connected by WLAN, while my host is connected with a cable.
The network on the host is also set to "private" and the VNC connection from the new PC to the Host works also without issues.

Basically the setting for all PCs in my home network is set to "Private network" and allow a VNC connection with this setting...

Any idea why this happens and how to allow VNC connections when network is configured as "private network" ?

I have searched the forum, but there are that many hits, that I might have overlooked the answer... Sorry for this.
But if anyone has an idea or the link to the answer for my problem this would be highly appreciated.

Thanks a lot.

Hermann

[rvk]

Then I changed network of the new PCs to a private network, but for both I got the message "Failed to connect to server!"
Switching back to public network VNC connection works again...

The first time connecting to your home network, you were TOO LATE to react on the message if you wanted internal computers to reach that computer. After that, that computer gets PUBLIC as network connection (instead of PRIVATE).

If you start a program which wants to receive outside connections, the Windows firewall will ask if it can make a rule for it. If you answer YES then that rule gets made for your PUBLIC profile. After switching to PRIVATE manually, that rule doesn't apply anymore (because it was only for PUBLIC, not PRIVATE). Once that rule was made, it won't prompt you again for it when you change the profile from Public to Private.

What you can do... Press Start and type Firewall, and choose "Windows Defender Firewall (control panel)". Then choose Allow an app or feature through Windows Defender Firewall. There you can see all the rules that are made.

If correct, you see that winvnc.exe (UltraVNC) is only allowed for "Public". Press Change settings and also check the Private box.

For better security you would want Public disabled, for when your computer gets connected to a strange network, but if that's never the case for you, you can leave it.

[Ludovic]

@ruckb, like @rvk has said, it is a problem of firewall/antivirus on your machines.
UltraVNC uses by default the 5900 tcp/udp port.
It is really important to have Private networks, it must be never "Public" for security reasons.