Digi TransPort WR31 User Manual page 218

Configure network interfaces
IP address
Enable standard Network Address Translation (NAT).
When a private IP host sends a UDP or TCP packet to an Internet IP address, the router changes
the source address of the packet from the private host IP to the router's public IP address before
forwarding the packet onto the Internet host. Additionally it will create an entry in a NAT table
containing the private IP source address, the private IP port number, the public IP destination
address and the destination port number. Conversely, when the router receives a reply packet
back from the public host, it checks the source IP, source port number and destination port
number in the NAT table to determine which private host to forward the packet to. Before it
forwards the packet back to the private host, it changes the destination IP address of the packet
from its public IP address to the IP address of the private host.
IP address and Port
Enable Network Address and Port Translation (NAPT).
This mode behaves like NAT but in addition to changing the source IP of the packet from the
private host it can also change the source port number. This is required if more than one private
host attempts to connect using the same local port number to the same Internet host on the
same remote port number. If such a scenario were to occur with NAT the router would be unable
to determine which private host to route the returning packets to and the connection would fail.
NAT Source IP address
If specified, and NAT mode is set to NAT or NATP for this interface, then the source address of
packets being sent out this interface is changed to this address, rather than the interface
address.
Enable IPsec on this interface
The IPSec parameter enables or disables IPSec processing on this interface. If this box is
checked, packets sent or received on this interface must pass through the IPSec code before
being transmitted. IPSec may drop the packet, pass it unchanged, or encrypt and encapsulate
within an IPSec packet.
Keep Security Associations (SAs) when this Mobile interface is disconnected
Configures the router to keep any existing IKE and IPsec associations should the link drop. This is
usually applied on head-end routers with fixed IP addresses.
Use interface X, Y for the source IP address of IPsec packets
By default, the source IP address for an IPSec Eroute is the IP address of the interface on which
IPSec was enabled. By setting this parameter to either a PPP or Ethernet interface, the source IP
address IPSec uses will match that of the Ethernet or PPP interface specified.
Enable the firewall on this interface
Turns Firewall script processing On or Off for this interface. If the firewall is enabled on an
interface and with the absence of any firewall rules, the default action is to block ALL traffic. To
configure the firewall, see the
Digi TransPort WR Routers User Guide
Firewall section.
Configure DSL interfaces
218