VNC User Guide - RealVNC

Chapter 2: Getting Connected
c. Click the Start button. RealVNC attempts to contact the host computer over the Internet. Providing
the host computer is connected to the Internet, the network address of an intermediary device is
revealed:
VNC Server appears to be behind a NAT router with IP address 212.44.6.81.
You will need to configure that router to forward port 5900 to this
computer before you can connect to VNC Server over the Internet.
Configuring a router to forward network communications
In a typical home or small office environment, a router assigns a private network address to an internal
computer. You should also be aware that VNC Server listens for network communications on a particular
port. The router must be configured to forward communications from VNC Viewer to the correct port at the
correct private network address. This procedure is known as port forwarding.
Note: Port forwarding instructions are specific to routers. If you do not have access to the host computer,
ask a host computer user to consult the manufacturer’s documentation, or visit www.portforward.com.
Note that a router may act as a public interface to more than one computer in a home or small office
environment. If you want to connect to multiple host computers, then VNC Server must be running on each
and listening on a different port. The router must be configured to distinguish between host computers using
port numbers.
Consider the following example:
A. Router with a network address assigned by an ISP, for example 212.44.6.81. B. Host computer with a network
address assigned by the router, for example 192.168.0.1. VNC Server is listening on the default port, 5900. C. Host
computer with a network address assigned by the router, for example 192.168.0.2. VNC Server has been configured to
listen on port 5901. D. Client computer running VNC Viewer.
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