40 | Chapter 3: Protecting Your Network
N300 Wireless Gigabit ADSL2+ Modem Router DGN3500 User Manual
Inbound Rules (Port Forwarding)
Because the wireless modem router uses Network Address Translation (NAT), your network
presents only one IP address to the Internet, and outside users cannot directly address any
of your local computers. However, by defining an inbound rule you can make a local server
(for example, a Web server or game server) visible and available to the Internet. The rule tells
the wireless modem router to direct inbound traffic for a particular service to one local server
based on the destination port number. This is also known as port forwarding.
Note: Some residential broadband ISP accounts do not allow you to run
any server processes (such as a Web or FTP server) from your
location. Your ISP might periodically check for servers and might
suspend your account if it discovers any active services at your
location. If you are unsure, refer to the acceptable use policy of your
ISP.
Remember that allowing inbound services opens holes in your firewall. Enable only those
ports that are necessary for your network. Following are two application examples of inbound
rules.
Inbound Rule Example: A Local Public Web Server
If you host a public Web server on your local network, you can define a rule to allow inbound
Web (HTTP) requests from any outside IP address to the IP address of your Web server at
any time of day. This rule is shown in the following figure:
Figure 18.
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