User`s guide

Configuration through the web interface
76
IP forwarding settings
When a Digi device acts as a router and communicates on both a private and public network with
different interfaces, it is sometimes necessary to forward certain connections to other devices. This
is also known as Network Address Translation (NAT) or Port Forwarding. When an incoming
connection is made to the device on the private network, the IP port is searched for in the table of
port forwarding entries. If the IP port is found, that connection is forwarded to another specific
device on the public network.
Port Forwarding/NAT is useful when external devices can not communicate directly to devices on
the public network of the Digi device. For example, this may occur because the device is behind a
firewall. By using port forwarding, the connections can pass through the networks transparently.
Also, Port Forwarding/NAT allows multiple devices on the private network to communicate to
devices on the public network by using a shared private IP address that is controlled by Port
Forwarding/NAT.
Port forwarding can be used to connect from a Digi device to a RealPort device. For this type of
connection to occur, your mobile wireless provider must be mobile-terminated.
IP Forwarding settings include:
 Enable IP Routing: Enables or disables IP forwarding.
 Apply the following static routes to the IP routing table: The Digi device can be
configured with permanent static routes. These routes are added to the IP routing table
when this device boots, or afterward when network interfaces become active or changes
are made to this list of static routes. The use of static routes provides a means by which
IP datagrams can be routed to a network that is not a local network or accessible through
the default route.
 Network Address Translation (NAT) Settings: A list of instances of NAT settings is
displayed. For each instance, the settings are:
– Enable Network Address Translation (NAT): Permit the translation and routing of IP
packets between private (internal) and public (external) networks. Refer to NAT
configuration options below. Some Digi device models permit the configuration of NAT
instances for more than one network interface. .
– NAT Public Interface: The name of the network interface for which NAT will perform
address and port translations. The list of interfaces available for NAT configuration
varies according to the capabilities of your Digi device model.
– NAT Table Size Maximum: The maximum number of entries that can be added to the
NAT table. These entries include the configured port and protocol forwarding rules (see
Forward TCP/UDP/FTP Connections and Forward Protocol Connections below), the
DMZ Forwarding rule (see Enable DMZ Forwarding to this IP address below), as well
as dynamic rules for connections that are created and removed during the normal
operation of NAT. The NAT table size maximum value may be configured for any value
in the range 64 through 1024, with the default value being 256 entries. Note that this
setting does not control the maximum number of port or protocol forwarding rules that
can be configured in their respective settings.