IP Port Forwarding / Static NAT Mappings parameters
Digi TransPort User Guide
379
IP Port Forwarding / Static NAT Mappings parameters
The router supports Network Address Translation (NAT) and Network Address and Port
Translation (NAPT). NAT or NAPT may be enabled on a particular interface such as a PPP instance.
When operating with NAT enabled, this interface has a single externally visible IP address. When
sending IP packets, the local IP addresses (for example on a local area network) are replaced by
the single IP address of the interface. The router keeps track of the local IP addresses and port
numbers so that if a matching reply packet is received, it is directed to the correct local IP address.
With only one externally visible IP address, NAT effectively prevents external computers from
addressing specific local hosts, thus providing a very basic level of “firewall” security.
Static NAT mappings allow received packets destined for particular ports to be directed to specific
local IP addresses. For example, to have a server, running on a local network, externally
accessible, a static NAT mapping would be set up using the local IP address of the server and the
port number used to access the required service.
Configuring IP port forwarding and static NAT mapping is done by entering the following
configuration values into a table and using the Add button to add them into the NAT
configuration for the router.
External Min Port
The lowest port number to be redirected.
External Max Port
The highest port number to be redirected.
Forward to Internal IP Address a.b.c.d
The IP address to which packets containing the specified destination port number are to be
redirected.
Forward to Internal Port
The IP port number to which packets containing the specified port number are to be
redirected. When set to
0
, no port remapping occurs and the original port number is used. The
NAT mode parameter of the appropriate interface must be set to
NAPT
rather than
NAT
or
OFF
for this parameter to take effect.
