TRENDnet TDM-C400 User's Guide - Page 127

Chapter 12. Configuring Network Address Translation Note The RDR rule: Allowing external access to a LAN computer You can create an RDR rule to make a computer on your LAN, such as a Web or FTP server, available to Internet users without having to obtain a public IP address for that computer. The computer's private IP address is translated to your public IP address in all incoming and outgoing data packets. Without an RDR rule (or Bimap rule described on page 133), the Ethernet Modem Router blocks attempts by external computers to access your LAN computers. The following example illustrates using the RDR rule to provide external access to your web server: Your ADSL2+ Ethernet Modem Router receives a packet containing a request for access to your Web server. The packet header contains the public address for your LAN as the destination IP address, and a destination port number of 80. Because you have set up an RDR rule for incoming packets with destination port 80, the device recognizes the data as a request for Web server access. The device changes the packet's destination address to the private IP address of your Web server and forwards the data packet to it. Your Web server sends data packets in response. Before the ADSL/ADSL2+ Ethernet Modem Router forwards them on to the Internet, it changes the source IP address in the data packets from the Web server's private address to your LAN's public address. To an external Internet user then, it appears as if your Web server uses your public IP address. Figure 52 shows the fields used to establish an RDR rule: Figure 52. NAT Rule - Add Page (RDR Flavor) 127