17 Bypassing a Firewall
Firewalls can pose a problem when using VNC. By far, the simplest and most secure
way to get around a firewall when using VNC is through SSH tunneling (Section
14.12).
But if the machine you??™re connecting to is a cluster of computers??”or if SSH is not
configured??”then SSH is not an option. However, you may be able to create the connection
if you reverse the direction: make the VNC server connect to the VNC
viewer.
To set up the viewer side of a reverse connection, run vncviewer with the -listen
argument. You can specify a port, or omit it and use the default of 5500 like this:
green$ vncviewer -listen
The server side is then set up in two steps. First, start the Xvnc server; here I??™m specifying
display :1 and instructing the server to connect to the display manager on red:
blue$ Xvnc -query red :1
If you??™re using a recent version of RealVNC, use the vncconfig command to instruct
the VNC server to connect to the viewer:
blue$ vncconfig -display :1 -connect blue:5500
If you??™re using TightVNC or an older version of RealVNC, the command is
vncconnect:
blue$ vncconnect -display :1 blue:5500
The port can be omitted if the default (5500) is used.
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