HTTP Through Firewall and "Bypass Proxy for Local Intranet"

"Bypass proxy server for local (Intranet) addresses" may not work as expected.

When a client process attempts to connect to an Internet address (for example, www.microsoft.com) through a proxy server when the above setting is selected, the first call to tcp_get_host_by_name uses that Internet server name (www.microsoft.com) as the server. Next, RPC sets up the tunneling, the proxy server redirects the call to the real server (www.microsoft.com), the response packet comes back to the proxy, the proxy redirects it back to the client, and the client sends it to the client process. However, the response packet contains the actual IP address of the Internet server. The client thinks that there is no proxy server and attempts to communicate directly to the Internet IP address that is unreachable; therefore, the connection fails.

If the "Bypass proxy server for local (intranet) addresses" setting is not selected, the call is always directed to the http proxy; however, if you do not select it, you may not be able to communicate or connect to Intranet servers.

The problem is that, if tcp_get_host_by_name() passes an address instead of a server name, it needs to force a name resolution to make sure the host is reachable.

To resolve this problem, obtain the latest service pack for Windows NT 4.0 or Windows NT Server 4.0, Terminal Server Edition. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

Microsoft has confirmed that this is a problem in Windows NT 4.0 and Windows NT Server 4.0, Terminal Server Edition. This problem was first corrected in Windows NT 4.0 Service Pack 4.0 and Windows NT Server 4.0, Terminal Server Edition Service Pack 4.