Problem:

You need to use the port-forwarding capability of the Digi ConnectPort WAN to remote control a machine on a network and that machine needs to maintain full connectivity to the local network and cannot have its gateway address changed. To forward traffic from the target machine through the Digi unit, the IP address of the Digi needs to be set as the target machine's gateway - which interferes with the machine's local network access.

Cause:

Whilst the Digi unit performs Network Address Translation on incoming packets it forwards to a host on the local network, it only rewrites the packet's target address, not the source address. Therefore, when connecting to the WAN IP address of the Digi, the Digi forwards that packet via its LAN interface to the target machine. The target machine, however, sees the incoming packet as having come from the external address of the machine that initiated the session, not the address of the LAN interface of the Digi. Therefore, when the target machine tries to respond to the request, it routes the data to the public address which needs to be routed to the machine's gateway address, not the Digi, and the connection is unsuccessful.

Resolution:

A static route can be added to the target machine at the command prompt to route all data to a specific IP address via a specific gateway address - only affecting traffic to that IP address.

At the command prompt, enter the following command:

route add <external address> <gateway address>

so, for example:

route add 62.189.60.194 192.168.1.99

This assumes, however, that you will always be connecting from the same IP address and that the target device allows for static routes to be defined on it (Windows-based PCs and Unix machines support this functionality).

This route will be lost if the device is rebooted. To make the route 'persistent', issue the same command with a '-p' at the end of the command.

To view routes that have been defined on a machine, issue the command 'route print' at the command prompt.

On a Windows PC, to remove a persistent route once it has been added, open Registry Editor and browse to the following folder:

HKEY_LOCAL_MACHINE \ SYSTEM \ CURRENTCONTROLSET \ SERVICES \ TCPIP \ PARAMETERS \ PERSISTENTROUTES

Locate the entry for the route and delete it, then reboot the PC.