What they tell you.
CONNECTION REFUSED
Something answered and declined the connection.
The host is reachable; the service is not accepting on that port.
CONNECTION TIMED OUT
Nothing answered.
Either the host is unreachable, or something is silently dropping the traffic.
WHY THE DISTINCTION MATTERS
Refused points at the service. Timed out points at reachability or filtering.
HOST NOT FOUND OR NAME NOT RESOLVED
DNS. The name did not resolve at all.
NETWORK UNREACHABLE
No route to the destination. Frequently a gateway problem.
CERTIFICATE ERRORS
The name does not match, the certificate expired, or the clock is wrong.
Check the clock before assuming a certificate problem.
TOO MANY REDIRECTS
A configuration loop, usually in the application or a proxy.
SERVICE UNAVAILABLE
The server is reachable and could not serve the request.
WHAT TO DO WITH ANY ERROR
Read the exact text.
It usually states precisely which layer failed.
