Transmission Control Protocol (TCP) port 443 is the default port used by Hypertext Transfer Protocol Secure (HTTPS). If this port is blocked on any server or device from your computer to a given destination, such as www.Microsoft.com, your connection to any https site will fail and your browser will return an error message like "Secure Connection Failed" or "Page Cannot be Displayed." However, the two most common locations for this failure are at your workstation or router.
Open a web browser and attempt to load several different https sites, such as your bank's website, and https://www.Microsoft.com. If at least one of these connections is successful, port 443 is open on your end. To determine if port 443 is open at a remote server address, follow Steps 2 through 4.
Click "Start" and position your cursor in the "Search" box.
Type "cmd" (no quotation marks) and press "Enter."
Type "telnet servername.domain.com 443" (replace "servername.domain.com" with any web server address using HTTPS. For example, Microsoft.com. If you get a blank screen with a flashing cursor, port 443 is open there. If the port is closed, you will receive a "Could not open a connection to host on port 443 : Connect failed" error message.
If you need to pinpoint the exact location where port 443 is blocked, type "tracert www.enterwebserveraddress.com --d" (no quotation marks). Replace the server address given for the destination server address and press "Enter." Your workstation will begin tracing the network path to the destination. Each "hop" represents an intermediate router or server the trace must travel through en route. You may check each of these "hop" locations by typing "telnet" (no quotation marks), followed by the first hop's IP address. Execute the command by pressing "Enter." The first address that gives you a "connect failed" error message represents the culprit device.
There are many web-based tools for determining which ports are opened or closed. However, since many hardware and software based firewalls block port scanning applications, using these tools may yield incorrect results.