Port Scanner

A Port Scanner is a network security utility used to discover "Open Doors" (Ports) on a remote server or IP address. Every internet service—like Websites (Port 80/443), Email (Port 25/587), or File Transfers (Port 21)—listens on a specific numerical port. This tool is mission-critical for system administrators performing "Vulnerability Assessments" and developers ensuring that only necessary services are exposed to the public internet.

Implementation & Processing Pipeline

The analysis engine audits network endpoints through a systematic probing pipeline:

1. TCP Connection Probing: The tool attempts to initiate a "TCP Three-Way Handshake" (SYN, SYN-ACK, ACK) with a range of common ports on the target IP.
2. Port Status Identification: Each probe results in a status:
   • Open: The server accepts the connection, meaning a service is actively listening.
   • Closed: The server explicitly rejects the connection.
   • Filtered (Stealth): There is no response, usually indicating that a Firewall is silently dropping the packets.
3. Service Inference: Based on the port number, the tool provides the "Standard Service" name (e.g., Port 22 is identified as SSH).
4. Sequential vs. Parallel Scanning: For speed, the tool probes multiple ports simultaneously, while respecting "Rate Limits" to avoid being flagged as a "Malicious Scan."
5. Reactive Dashboard: The results are displayed in a clean list, highlighting "High Risk" open ports that should typically be closed on a production server.

How It's Tested

We certify the scanning engine against known server configurations to ensure accuracy.

1. The "Open Port" Verify:
   • Action: Scan scanme.nmap.org (authorized target) for Port 80.
   • Expected: Status must be "OPEN" (Service: HTTP).
2. The "Closed Port" Logic:
   • Action: Scan a random high port (e.g., 55555) on a standard server.
   • Expected: Status must be "CLOSED" or "FILTERED".
3. The "Timeout" Safety:
   • Action: Scan a non-routable IP (e.g., 10.255.255.1).
   • Expected: The tool must report "Unreachable" or timeout gracefully after 5 seconds, not hang indefinitely.
4. The "Service Text" Check:
   • Action: Identify Port 443.
   • Expected: Label is correctly shown as "HTTPS (Secure Web)".

The History of Port Scanning

The practice of scanning ports is nearly as old as the TCP/IP protocol itself (1983).

• SATAN (1995): The "Security Administrator Tool for Analyzing Networks" was one of the first to automate vulnerability checks, causing panic in the media that it would "Help Hackers."
• Nmap (1997): Gordon Lyon (Fyodor) released Nmap, which became the industry standard. It was so iconic it appeared in movies like The Matrix Reloaded.