What is TCP Port?

A TCP port is a numbered endpoint (ranging from 0 to 65,535) that identifies a specific network service on a device. When a service listens on a TCP port, it accepts incoming connections on that port number. Port 80 is HTTP, port 443 is HTTPS, port 22 is SSH, and port 3389 is RDP.

Port categories

  • Well-known ports (0-1023) - assigned to standard services by IANA (HTTP, HTTPS, SSH, SMTP, DNS)
  • Registered ports (1024-49151) - assigned to specific applications (MySQL 3306, PostgreSQL 5432, RDP 3389)
  • Dynamic/ephemeral ports (49152-65535) - used temporarily for client-side connections

Security significance

An open TCP port is a potential entry point for attackers. Port scanning - systematically probing ports to discover which are open - is the first step in most network reconnaissance. Every open port increases the attack surface. SurfaceLoop scans for open TCP ports across all your external IP addresses and identifies the services running on them.

Map your attack surface - first scan free