D-Link DSL-2600U User Manual page 36

Web Configuration
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.
=
Using port forwarding (the forwarding of requests to particular ports), the router is forced to send requests from the Internet for a certain service, for example, a game,
to the appropriate port(s) on the PC on which the game is running. Port triggering is a special variant of port forwarding. Unlike port forwarding, the DSL router
forwards the data from the port block to the PC which has previously sent data to the Internet via a certain port (trigger port). This means that approval for the data
transfer is not tied to one specific PC in the network, but rather to the port numbers of the required Internet service. Where configuration is concerned, you must
define a so-called trigger port for the application and also the protocol (TCP or UDP) that this port uses. You then assign the public ports that are to be opened for the
application to this trigger port. The router checks all outgoing data for the port number and protocol. If it identifies a match of port and protocol for a defined trigger port,
then it opens 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, the
router allows it to pass through and directs it to the appropriate PC. A trigger event always comes from a PC within the local network. If a trigger port is addressed
from outside, the router simply ignores it.
Note:
=
An application that is configured for port triggering can only be run by one user in the local network at a time.
=
After public ports are opened, they can be used by unauthorized persons to gain access to a PC in the local network.
=
When the DSL router is supplied, the NAT function is activated. For example, all IP addresses of PCs in the local network are converted to the public IP address of the
router when accessing the Internet. You can use NAT settings to configure the DSL router to carry out the following tasks.
=
For functions described as follows, IP addresses of the PCs must remain unchanged. If the IP addresses of the PCs are assigned via the DHCP server of the DSL
router, you must disable DHCP server as the settings in the local network menu entry for the lease time or assign static IP addresses for the PCs.
You can enable or disenable the NAT function. By default, the NAT function is enabled.
NAT-Virtual Server Setup
By default, DSL router blocks all external users from connecting to or communicating with your network. Therefore, the system is safe from hackers who may try to intrude
into the network and damage it.
However, you may want to expose your network to the Internet in limited and controlled ways in order to enable some applications to work from the LAN (for example,
game, voice, and chat applications) and to enable Internet access to servers in the home network. The port forwarding feature supports both functionalities. This topic is
also referred as Local Servers.
The port forwarding page is used to define applications that require special handling by DSL router. All you need to do is to select the application protocol and the local IP
address of the computer that is using or providing the service. If required, you may add new protocols in addition to the most common ones provided by DSL router.
For example, if you wanted to use a file transfer protocol (FTP) application on one of your PCs, you would simply select FTP from the list and enter the local IP address or
host name of the designated computer. All FTP-related data arriving at DSL router from the Internet henceforth is forwarded to the specific computer.
Similarly, you can grant Internet users access to servers inside your home network, by identifying each service and the PC that provide it. This is useful, for example, if you
want to host a Web server inside your home network.
When an Internet user points his/her browser to DSL router external IP address, the gateway forwards the incoming HTTP request to your Web server. With one external
IP address (DSL router main IP address), different applications can be assigned to your LAN computers, however each type of application is limited to use one computer.
D-Link DSL-2600U User Manual
33