Since my hard drive recently crashed and I had to reinstall my Windows XP (yes, I have not yet moved on to Vista nor Windows 7), I took the opportunity to install Service Pack 3. For some strange reason, my previous SP2 installation would get strange errors when I try to install SP3. So this time around, I went straight to SP3.
For the past week, I've been testing some applications to require a PC outside my LAN to access my XP's web server (aka. IIS). The http connection cannot seem to get through. I use Comodo Internet Security for my firewall, and as far as I can tell, my firewall rules should allow HTTP to come in. After a couple of days of tinkering, it finally occurred to me that the problem might be related to SP3.
After a little bit of Google research, I found that out that XP+SP3, by default, runs Windows Firewall that blocks incoming traffic including port 80. I assumed that when one installs a 3rd party firewall or anti-virus, it disables the built-in one from Windows. But in this case, even though I had Comodo running, the internal Windows Firewall was still active.
To fix the problem:
- Start >> Run "firewall.cpl"
- Go to Exceptions tab
- "Add Port" for port 80
That's it! After that, incoming HTTP is working again.