D-Link DSR-250 Product Manual - Page 47

Unified Services Router User Manual your ISP has assigned an IP address for each of the computers that you use, select Classic Routing.  NAT is a technique which allows several computers on a LAN to share an Internet connection. The computers on the LAN use a "private" IP address range while the WAN port on the router is configured with a single "public" IP address. Along with connection sharing, NAT also hides internal IP addresse s from the computers on the Internet. NAT is required if your ISP has assigned only one IP address to you. The computers that connect through the router will need to be assigned IP addresses from a private subnet.  Transparent routing between the LAN and WAN does not perform NAT. Broadcast and multicast packets that arrive on the LAN interface are switched to the WAN and vice versa, if they do not get filtered by firewall or VPN policies. To maintain the LAN and WAN in the same broadcast domain select Transparent mode, which allows bridging of traffic from LAN to WAN and vice versa, except for router-terminated traffic and other management traffic. All DSR features (such as 3G modem support) are supported in transparent mode assuming the LAN and WAN are configured to be in the same broadcast domain.  NAT routing has a feature called ―NAT Hair-pinning‖ that allows internal network users on the LAN and DMZ to access internal servers (eg. an internal FTP server) using their externally-known domain name. This is also referred to as ―NAT loopback‖ since LAN generated traffic is redirected through the firewall to reach LAN servers by their external name. 45