User`s guide

183
IP Port Forwarding / Static NAT Mappings
Configuration – Network > IP Routing / Forwarding > IP Routing /Static NAT
Mappings
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 value in this text box specifies the lowest port number to be redirected.
External Max Port
The value in this text box specifies the highest port number to be redirected.
Forward to Internal IP Address a.b.c.d
The value in this text box is the IP address to which packets containing the specified
destination port number are to be redirected.
Forward to Internal Port
The value in this text box specifies 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.
Related CLI Commands
Entity
Instance
Parameter
Values
Equivalent Web Parameter
nat 0 - 29 minport 0 - 65535 External Min Port
nat 0 - 29 maxport 0 - 65535 External Max Port
nat 0 - 29 IPaddr
Valid IP address
a.b.c.d
Forward to Internal IP Address
a.b.c.d
nat 0 - 29 mapport 0 - 65535 Forward to Internal Port
Command format:
Nat <entry> <parameter> <value>
Example commands: