General ยป  VNC

VNC: Port Forwarding

What is Port Forwarding

Typically most organisations have a single network router connected to the internet for access. This router will have a unique public facing IP address which by definition is accessible by anyone on the internet.

A port number is a number from 0 to 65535 that is linked to the IP address of a network device. Software/Firmware on the network device binds exclusively to one or more of these ports for communication to provide a service. The most famous port number is 80, which is normally associated with a web server for delivering web pages such as this. A list of well-known port numbers can be found on Wikipedia. All Adder VNC based products use port 5900 by default, however, this is customisable.

Port forwarding allows external network devices to communicate with a network device that is within an organisations network, also known as a private LAN (Local Area Network). This is done by assigning a specific port number to the external routers IP address and forwarding it to an internal private IP address and port number of a network device on the private LAN. From an outsiders point of view, it appears as though the router is delivering the service.


As the configuration of a router varies between different makes and models, providing the port forwarding configuration for your specific router and/or firewall is beyond the scope of this page and support, please consult your system administrator.

This will give you an overview and understanding of how you can connect an Adder product running a VNC server to your network and enable remote access.

VNC PortForwarding

The diagram above shows the following elements:-

  • A Remote User, it is assumed that they already have internet access and is running a VNC Viewer client.
  • An internet router.whose unique public IP address is 123.456.789.1 and the internal private IP address is This is the gateway IP address used by internal network devices to access the internet,
  • An Adder IPEPS whose internal LAN IP address is and port number is 5900. A gateway IP address will also need to be set on the IPEPS, this is normally the IP address of the router which in this case is
  • Port 5901 has been chosen for the external public facing port and configured on the internet router forward traffic to IP address and port 5900.

The port forwarding configuration will differ between makes and models of router/firewall, however, it typically will require information such as:-

VNC PortForwarding3

  • Application - a name for the port forwarding service that you are setting up.
  • IP Address - the internal IP address of the network device that you are forwarding to.
  • Start - the port number that is open on the public side of the router.
  • End - the port that is open on the internal network device.
  • Protocol - for VNC this needs to be TCP. For other services, this can be UDP or both TCP and UDP.
  • Enabled - forwarding for this port is active.

For the Remote User to connect to the VNC device, they would enter the routers public IP address followed by a colon ':' and then port number, e.g. <IPADDRESS>:<PORT>. In this example, the connection address will be 123.456.789:5901:-

VNC PortForwarding2

Further Information

With port forwarding, it is possible to have remote access to multiple VNC products on the internal private LAN. For example, let's imagine that you have a number of Adder VNC sources available. You can assign an individual external port number to each one and then forward them appropriately to each Adder product.

The table below shows an example of the port forwarding settings and the IP address that you would use to access them externally:-

VNC PortForwarding4


  • Make sure that the Remote Users own firewall or router is not blocking outbound connections to the remote VNC port.
  • Likewise, if you are using a firewall on the organisations network, make sure that traffic is allowed to pass through from the external router to the Adder product running VNC.

Page last modified on Thursday April 11, 2019 12:36:38 GMT-0000