Port Checker Tool: Real-Time Open Port Scanner
Understanding Port Status and Connectivity
In computer networking, a port is a logical communication endpoint that identifies a specific process or type of network service. When you attempt to connect to a server (like a website or an email server), your computer connects to a specific IP address and a specific port number.
What Do the Results Mean?
When using the Port Checker, you will encounter three primary status types:
- Open: The target server is actively listening on this port and accepting connections. This usually means the service (like a web server on port 80) is running and accessible.
- Closed: The request was received by the server, but no application is listening on that port. This indicates the host is up, but the service is down or not configured.
- Filtered (or Dropped): The request never reached the target port. This is almost always caused by a firewall (either on your network, the ISP, or the destination server) blocking the packet explicitly.
Common Ports Reference
While there are 65,535 available ports, most internet traffic uses a small subset of "Well-Known Ports" (0-1023).
| Port | Protocol | Service | Usage |
|---|---|---|---|
| 21 | TCP | FTP | File Transfer |
| 22 | TCP | SSH | Secure Remote Login |
| 80 | TCP | HTTP | Standard Web Traffic |
| 443 | TCP | HTTPS | Secure Web Traffic |
| 3389 | TCP | RDP | Remote Desktop Protocol |
How Firewall Latency Works
Latency, often called Round-Trip Time (RTT), is the time it takes for a data packet to travel from the source to the destination and back. In networking equations, Total Delay (\( T_{delay} \)) is often approximated as:
\[ T_{delay} = T_{prop} + T_{trans} + T_{proc} + T_{queue} \]
Where \( T_{prop} \) is propagation delay (distance), \( T_{trans} \) is transmission delay (bandwidth), \( T_{proc} \) is processing delay (router/firewall CPU), and \( T_{queue} \) is queuing delay. This tool measures the aggregate RTT, helping diagnose if a specific port is responding slowly due to firewall inspection overhead or network congestion.