Configuration with Advanced Setup

Configuring Special Applications

One property of NAT is that data from the Internet is not allowed into your local network unless it has been explicitly requested by one of the PCs on that network. Most Internet applications run behind the NAT Firewall without any problems. If you request Internet pages, for example, or send and receive emails, the request for data from the Internet comes from a PC on the local network and so the router allows the data through. The router opens exactly one Port for the application. If an external application tries to send a call to a PC within the local network, the router will block it. There is no open port via which the data could enter the local network.

Some applications, such as games, network conferences and voice over the Internet, require several links, i.e. several ports, so that the users can communicate with each other. In addition, these applications must also be permitted to send requests from other users on the Internet to the user on the local network. These applications cannot work if Network Address Translation (NAT) has been activated. If you want to use such applications nevertheless, then you will have to configure them as Special Applications. This means:

◆You define a so-called trigger port for the application and assign it the public ports that have to be opened for the application.

◆The router checks all outgoing data for the port number. If it recognises a match with a defined Trigger Port, then it will open the assigned public ports and notes the IP address of the PC that sent the data. If data comes back from the Internet via one of these public ports, it allows the data through and directs it to the right PC. A trigger event always comes from a PC within the local network. If a Trigger Port is addressed from outside, it is simply ignored by the router.

iYou will find a detailed example of how to configure special applications in "Practical Tips and Configuration Examples" on the supplied CD.

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