I have a lan of about 10-15 clients (depends on counting tablets and so on..). To access them from one station I use tightvnc which works like a charm - up to now. Sometimes I cannot access and I don't know why. When I access manually and so on, then it works, out of the blue. Are there some commonly known "features" I don't know?
closed as too broad by Rui F Ribeiro, Thomas Dickey, Jeff Schaller♦, msp9011, Totor Sep 5 '18 at 6:23
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VNC works on ports 5900 and up; 5900 for the service I believe then 5900+n for each n user desktops.
so if you are the 7th user for example and you get desktop :7, you would need port 5907 in addition to 5900 being opened in your firewall.
depending on your linux distribution, they sometimes manage only a few ports upward or 5900, your 10-15 clients is likely exceeding that and your firewall may be blocking VNC for those desktops.
a not uncommon but not necessarily correct practice is to just open ports 5900:5999 in your firewall, which would account for up to 99 users... or disable firewall if that is acceptable on your LAN