How to configure NAT Static Mappings on Diva ADSL Routers

When are NAT static mappings required?

NAT static mappings are required when a user wishes to route a certain type of Internet traffic to a specific computer on the internal LAN and still maintain Network Address Translation for security. 

A typical example of this is when a user requires all http traffic (i.e. web requests) to be routed ("mapped") to a web server behind the Diva 2440. Doing this via mapping as opposed to direct routing maintains the security of Network Address Translation which guards against hacking. 

Note: The instructions on this page apply to both the Diva 2440 and 2480 provided they have version 1.5 and above of the firmware.

How do I configure NAT Static Mappings?

In order to demonstrate how to set up NAT static mappings, we will go through how to route http traffic to a web server. However it should be possible to apply exactly the same principals to whatever mapping is required. - e.g. an FTP server.

Step 1: 

Go to the configuration page of the Diva 2440 by typing 192.168.1.1 in your browser address bar. Get to the NAT settings page by clicking 'Advanced settings'-> 'NAT Server Settings'. 

You should see the following:

Step 2: 

Click on the 'View Mappings' button. You will see the following screen:

Step 3:

 In the above screenshot there are no NAT server mappings currently configured. To add a server mapping click on the 'Add Server' button. You should then see the following screen:

Step 4: 

You must now choose which type of traffic you wish to create a mapping for. In our example, we wish to route web traffic and have therefore chosen to create a mapping for HTTP traffic. Once you have selected the appropriate type of traffic, click on the 'Next' button. 

Step 5: 

You must now specify the details of the mapping that you wish to create. You should fill in the four fields as follows:

• Server Name: You can give any name to your server, however, in our example, since we are routing web traffic, it has been given the default name of 'HTTP'.
• IP Address: You should enter the IP address of the server that you wish to route traffic to - e.g. 192.168.1.3
• Protocol: The type of IP protocol used by this traffic - in this case, TCP
• Port: The port on the server to which traffic should be routed. Web servers customarily use Port 80.

Note: If you are mapping something other than web traffic, click on the subject headers for help on each item.

For our sample mapping, the screen should now look as follows:

The NAT static mapping seen above specifies that all HTTP traffic coming in to the 2440 via TCP on port 80 - the port reserved for http ("web") traffic - should be forwarded to the server specified by the Server IP address - in this case, 192.168.1.3.

Note: This server IP address will need to be reserved for the particular PC concerned by specifying it on the PC instead of acquiring it via DHCP - which is the normal IP setup method. You would do this in the TCP/IP Protocol settings screen within the Windows 'Network' setup screens for the LAN card on the PC which is to be the web server.

Step 6: 

Click on the save button and wait while your mapping is being saved. Once this is done you should see the following screen:

Your NAT static mapping has now been created.

Now, when a web service request arrives at the Diva ADSL Router from the Internet, the router knows that it is destined for the PC on IP address 192.169.1.3 and will forward the packet to it. The web server will then find the relevant web page that has been requested, and send it back out to the router which in turn will forward it on to the original address of the requesting PC on the Internet. 

The requesting PC never gets to know the IP address of the web server behind the Diva ADSL Router, so security is maintained. The delivery of the web service request is achieved by "mapping" any web requests received by the router to the IP address of the web server PC using NAT Static Mappings.