Nat - D-Link DSL-500B User Manual

Web Configuration

NAT

Note: You must enable the NAT service when you configure the WAN connection at first. The NAT item will then
appear in the Advanced Setup directory. In the pure bridging mode, there is no NAT service.
Overview - Setting up the NAT Function
The DSL router is equipped with the Network Address Translation (NAT) function. With address mapping, several
users in the local network can access the Internet via one or more public IP addresses. All the local IP addresses
are assigned to the public IP address of the router by default.
One of the characteristics of NAT is that data from the Internet is not allowed into the local network unless it is
explicitly requested by one of the PCs in the network. Most Internet applications can run behind the NAT firewall
without any problems. For example, if you request Internet pages or send and receive e-mails, the request for data
from the Internet comes from a PC in the local network, and so the router allows the data to pass through. The
router opens one specific port for the application. A port in this context is an internal PC address, via which the data
is exchanged between the Internet and a client on a PC in the local network. Communicating via a port is subject to
the rules of a particular protocol (TCP or UDP).
If an external application tries to send a call to a PC in the local network, the router blocks it. There is no open port
via which the data could enter the local network. Some applications, such as games on the Internet, require several
links (that is, several ports), so that players can communicate with each other. In addition, these applications must
also be permitted to send requests from other users on the Internet to users in the local network. These applications
cannot run if NAT is activated.
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