Billion BiPAC 7300 RA User Manual page 89

Since NAT acts as a "natural" Internet firewall, your router protects your network from
access by outside users, as all incoming connection attempts point to your router unless
you specifically create Virtual Server entries to forward those ports to a PC on your network.
When your router needs to allow outside users to access internal servers, e.g. a web server,
FTP server, Email server or game server, the router can act as a "virtual server". You can
set up a local server with a specific port number for the service to use, e.g. web/HTTP (port
80), FTP (port 21), Telnet (port 23), SMTP (port 25), or POP3 (port 110). When an incoming
access request to the router for a specified port is received, it is forwarded to the
corresponding internal server.
For example, if you set the port number 80 (Web/HTTP) to be mapped to the IP Address
192.168.1.2, then all incoming HTTP requests from outside users are forwarded to the local
server (PC) with the IP address of 192.168.1.2. If the port is not listed as a predefined
application, you need to add it manually.
In addition to specifying the port number used, you also need to specify the protocol used.
The protocol is determined by the particular application. Most applications use TCP or UDP,
however you can specify other protocols using the drop-down Protocol menu. Setting the
protocol to "all" causes all incoming connection attempts using all protocols on all port
numbers to be forwarded to the specified IP address.
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