I have three Windows hosts on the same private LAN, each hosting an IIS default website. One host is running Windows 7 Pro, while the other two are running Windows 8.1 Update Version 6.3 (Build 9600).
Other computers on the local subnet can open the default website on each of the 3 hosts by entering each host's private IP address in a browser.
However, when I Port Forward port 80 from a gateway router in turn to each of the 3 hosts private IP address, then enter the gateway router's public IP into a browser on a computer outside of the private network, only the Windows 7 host displays its default website. The two Windows 8.1 Update hosts report "This webpage is not available. Details: The host took too long to respond." Additionally, no record of the HTTP request appears in "C:\inetpub\logs\LogFiles\W3SVC1\u_exYYMMDD.log" on the host.
All three hosts have their Windows Firewall Inbound Rule "World Wide Web Services (HTTP Traffic-In)" set to Profile: All, Enabled: Yes, Action: Allow, Override: No, Program: System, Local Address: Any, Remote Address: Any, Protocol: TCP, Local Port: 80, Remote Port: Any, Authorized Users: Any, Authorized Computers: Any, Authorized Local Principles: Any, Local User Owner: Any, Application Package: Any.
Furthermore, disabling both Windows Firewall and Windows Defender made no difference. I have no other security or firewall systems installed.
Something is preventing port 80 requests from public ip addresses from reaching Windows 8.1 Update IIS. But the success on Windows 7 demonstrates that the gateway router is properly forwarding outside traffic to the assigned IP address.
This problem only appeared after I installed the mid-February Windows Update. Any help diagnosing & fixing the problem is greatly appreciated.