I have x11vnc server set up on a Lubuntu 14.04 system, using ~/.config/autostart/x11vnc.desktop to start it.
For a long time I specified exactly which machines on my network could access the server using:
Exec=x11vnc -forever -allow 172.27.123.2,172.27.123.3,172.27.123.4,172.27.123.5,172.27.123.6 -httpport 5900
However, because I do not want to manually add a new device every time, and having read the manual page for the -allow option:
By ending in a ".", it can also be a numerical IP prefix, e.g. "192.168.100." to match a simple subnet
I decided to change this line of the x11vnc.desktop file to:
Exec=x11vnc -forever -allow 172.27.123. -httpport 5900
However when I rebooted with these settings, I could not connect to the VNC server from any machine on the 172.27.123.0/24 subnet.
I also tried:
Exec=x11vnc -forever -allow "172.27.123." -httpport 5900
Exec=x11vnc -forever -allow 172.27.123.0/24 -httpport 5900
But was still unable to connect.
Why might this be happening, and what can I do to use the -allow option to allow access from a subnet?