The disappearing local website

Problem: I have set the ports up correctly so that incoming HTTP is forwarded to a machine on my network. From work or via dialup I can see my test website, but I cannot see it when I access it from broadband at home.

The problem you have is with the way that NAT (Network Address Translation) works, not with the way that the DSL-500/DSL-504 router works.

NAT: An HTTP request from inside the LAN has a source private IP address which NAT translates to a public IP address when a packet goes out through the external (WAN) interface, the destination public IP address is untouched. When the response comes back through the external (WAN) interface, NAT translates the destination IP address back to the private IP address, the source public IP address is untouched.

In the case under discussion, the request never goes out through the external (WAN) interface (as the web server's public IP address is not out on the Internet, but on the router's external interface), so its source IP address is never touched. And it never comes back through the external (WAN) interface so the destination IP address is never touched. The result is that the web server never receives the request; the TCP connection simply times out in the router's TCP connection table.

Solution: You have some options:

• Access your website using its private IP address;
• Access your website through an external web proxy (eg www.anonymizer.com);
• Edit your hosts file (Unix/Windows) to resolve your web server name to the private IP address (this file is generally consulted before external DNS is consulted);
• Install a local DNS server which will resolve your domain to its private IP address instead of its public IP address.

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