Testing Basic HTTP Connectivity
The very first step is to determine whether your web server is accessible on TCP port 80 (HTTP).
Lack of connectivity could be caused by a firewall with incorrect permit, NAT, or port forwarding rules to your Web server. Other sources of failure include Apache not being started at all, the server being down, or network-related failures.
If you can connect on port 80 but no pages are being served, then the problem is usually due to a bad Web application, not the Web server software itself.
It is best to test this from both inside your network and from the Internet. Troubleshooting with TELNET is covered in Chapter 4, "Simple Network Troubleshooting".