Digi WAN 3G User Manual page 87

C o n f i g u r e D i g i d e v i c e s
IP pass-through settings
There are many application scenarios where a router is used to decide upon alternative routes using
a primary and a secondary (or backup) interface. In many of these configurations, the router is
required to use a public IP address as assigned by the network over which it is communicating.
This requirement is mostly owing to the router needing to establish a VPN tunnel over that
interface and using the public IP address as part of the VPN authentication. (For more on VPN
tunnels, see page 79.)
The IP pass-through feature allows a Digi device to provide bridging functionality similar to that of
a cable or DSL modem, where the Digi device becomes "transparent" to the router or connected
device. In this case; the router's WAN interface believes it is connected directly to the mobile
network and has no knowledge that the Digi device is the mechanism providing that connectivity.
How IP pass-through works
A Digi device configured for IP pass-through, such as a ConnectPort WAN or Digi Connect WAN,
passes its mobile IP address directly through and to the Ethernet device (router or PC) to which it is
connected through the Ethernet port. From the perspective of the connected device, the Digi device
essentially becomes transparent (similar to the behavior of a cable or DSL modem) to provide a
bridge from the mobile network directly to the end device attached to the Digi device.
Since the mobile network address is effectively "passed-through" to the local device connected to
the Ethernet port of the Digi device, all network access to it is bypassed, with some specific
exceptions.
Here is an example of a Digi device configured for IP pass-through in a network with a third-party
router.
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