As part of troubleshooting a system, testing network connectivity and working communication channels is pretty important.
For example, to test an HTTP server, use these commands:
telnet www.google.com 80
GET / HTTP/1.0
with 2 enters after the GET line. Then you will get to see exactly how the server responds.
Sometimes it would be nice to test an SSL connection, to see what the server is saying. Thanks to Tony Copping for showing me this.
openssl s_client -showcerts -connect www.google.com:443