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Ports

Port Ranges​

  • Well-known Ports (0-1023): For system-wide services and standards. Require root privileges to open
  • Registered Ports (1024-49151): For user-defined or less common services
  • Dynamic/Private Ports (49152-65535): Temporarily assigned for client-side communications

Network Tools​

nmap​

Network scanner for checking open ports and services on remote systems.
Documentation

nmap <IP-Address>

netstat​

Display open ports and associated services.
Documentation

netstat -tuln

ss​

Modern alternative to netstat for displaying network connections.
Documentation

ss -tuln

lsof​

List open files and associated processes, useful for checking open ports.
Documentation

lsof -i

Firewall Configuration​

iptables or nftables​

Manage Netfilter firewall rules.
Documentation
IptablesHowTo

ufw (Uncomplicated Firewall)​

User-friendly frontend for iptables.
Documentation

ufw allow 22/tcp

Security Considerations​

  • Avoid unused ports: Disable or close unused ports to reduce the attack surface.
  • Use secure protocols: Prefer encrypted protocols (e.g., SSH instead of Telnet, HTTPS instead of HTTP).
  • Firewall rules: Configure firewall rules to restrict access to open ports.

Commonly Used Ports​

Port 20/21 (FTP)​

  • Usage: File Transfer Protocol (FTP)
  • Port 20: Data transfers
  • Port 21: Control (commands and responses)

Port 22 (SSH)​

  • Usage: Secure Shell (SSH) for secure remote connections and file transfers (SCP, SFTP)
  • Standard services: OpenSSH

Port 23 (Telnet)​

  • Usage: Unencrypted terminal protocol for remote connections (not secure and largely replaced by SSH)

Port 25 (SMTP)​

  • Usage: Simple Mail Transfer Protocol (SMTP) for sending emails
  • Standard services: Postfix, Sendmail

Port 53 (DNS)​

  • Usage: Domain Name System (DNS) for name resolution
  • Standard services: BIND, dnsmasq

Port 80 (HTTP)​

  • Usage: Hypertext Transfer Protocol (HTTP) for unencrypted web communication
  • Standard services: Apache, Nginx

Port 110 (POP3)​

  • Usage: Post Office Protocol Version 3 (POP3) for retrieving emails
  • Standard services: Dovecot, qpopper

Port 143 (IMAP)​

  • Usage: Internet Message Access Protocol (IMAP) for retrieving and managing emails
  • Standard services: Dovecot, Courier

Port 443 (HTTPS)​

  • Usage: Hypertext Transfer Protocol Secure (HTTPS) for encrypted web communication
  • Standard services: Apache, Nginx

Port 3306 (MySQL/MariaDB)​

  • Usage: MySQL database server
  • Standard services: MySQL, MariaDB

Port 5432 (PostgreSQL)​

  • Usage: PostgreSQL database server
  • Standard services: PostgreSQL

Port 6379 (Redis)​

  • Usage: In-memory data structure store
  • Standard services: Redis

Port 8080 (HTTP Alternate)​

  • Usage: Alternate HTTP port, often used for development purposes
  • Standard services: Apache Tomcat, Spring Boot

Resources​