How do I troubleshoot intermittent or isolated network problems, like the inability to contact some web servers from my workstation?

If you can contact most, but not all of the websites you would like to visit with your workstation, the issue is most likely a network issue or a server issue:

In the event that you suspect a network issue, the problem is most likely with a firewall device on your network. It may be blocking access to various websites, based on domain name, IP address, or possibly even server port numbe...