What Does Checking Port Mean?

Corporate and educational networks often block incoming network traffic.

Applications establish network connections using numbered ports. Server software, such as game servers and file-sharing programs, requires that a port can receive incoming connections from the Internet. Many of these applications check that their ports can receive incoming connections, ensuring that the network is configured correctly. An error message indicates that the program won’t work correctly until its port can receive incoming connections.

Routers and Firewalls

Routers perform “network address translation” to share a single Internet address with multiple devices on a local network. Routers using network address translation discard incoming network traffic by default because the router doesn’t know which computer to send the traffic to. This causes the port to appear closed. Firewalls, including the firewall included with Windows, can also block incoming traffic, causing the port to appear closed.

Automatic Port Forwarding

Many routers support the UPnP or NAT-PMP protocols, which allow applications to automatically forward ports on the router. When an application that supports the protocol starts, it contacts the router and specifies its desired port. The router automatically forwards the port; you don’t have to enter the router’s Web interface and set it yourself.

Manual Port Forwarding

You can forward ports manually from your router’s Web interface. Type the router’s IP address, often “192.168.1.1,” into your Web browser’s address bar and press “Enter” to access its Web interface. Consult your router’s documentation or your router manufacturer’s website to determine its exact IP address, username and password. After you’re logged in, look for the “Port Forwarding” or “Virtual Server” section and forward the exact port your application requires to your computer’s local IP address.

Firewall Settings

Firewalls block incoming network traffic, making ports appear closed even if they’re forwarded correctly on the router. You can unblock an application on the Windows firewall by clicking “Start,” typing “Firewall,” clicking the “Allow a Program Through Windows Firewall” shortcut that appears and pressing “Enter.” Click the “Change Settings” button, click the check boxes to the right of your application and click “OK.” Consult your application's documentation if you use a different firewall

Checking Port

Applications check a port to ensure that it’s correctly forwarded, open and can receive incoming traffic. The application contacts a server, which attempts to establish an incoming connection to the port. A successful check indicates that your network is correctly configured, while a failure indicates that you must forward the port yourself or open it in any firewalls.

References

• Microsoft: Allow a Program to Communicate Through Windows Firewall
• Netgear: How Is Port Forwarding Configured?