Port Scanner

Check which ports are open on a host. Useful for security auditing and service discovery.

Common Ports Reference

21
FTP
22
SSH
23
Telnet
25
SMTP
53
DNS
80
HTTP
110
POP3
143
IMAP
443
HTTPS
445
SMB
3306
MySQL
3389
RDP
5432
PostgreSQL
5984
CouchDB
6379
Redis
8080
HTTP Alt
8443
HTTPS Alt
27017
MongoDB

Understanding Port Scanning

What is Port Scanning?

Port scanning is a technique to determine which ports on a network host are open (accepting connections), closed (rejecting connections), or filtered (blocked by a firewall).

Common Ports

  • 21 - FTP
  • 22 - SSH
  • 80 - HTTP
  • 443 - HTTPS
  • 3306 - MySQL
  • 5432 - PostgreSQL

Port States

  • Open: Service listening on port
  • Closed: Port actively rejects connections
  • Filtered: Firewall blocks probe
  • Stealth: Port hidden from scanner

Scanning Methods

TCP Connect:

Completes full three-way handshake. Slower but more reliable.

SYN Scan:

Sends SYN packets without completing handshake. Fast but may be detected.

UDP Scan:

Tests UDP services. Slower and less reliable than TCP.

Ping Sweep:

Sends ICMP pings to find active hosts before detailed scanning.

Legal & Ethical Considerations

Important: Only scan systems you own or have explicit permission to scan. Unauthorized port scanning may be illegal.

  • Always get written permission before scanning
  • Scan your own systems for security testing
  • Used in penetration testing and vulnerability assessment
  • Part of network security best practices
  • Use for CCNA/CompTIA certifications