| 20 | TCP | FTP-DATA | File Transfer Protocol – data transfer |
| 21 | TCP | FTP | File Transfer Protocol – control |
| 22 | TCP | SSH | Secure Shell – encrypted remote access |
| 23 | TCP | Telnet | Telnet – unencrypted remote access (deprecated) |
| 25 | TCP | SMTP | Simple Mail Transfer Protocol – email sending |
| 53 | TCP/UDP | DNS | Domain Name System – hostname resolution |
| 67 | UDP | DHCP | Dynamic Host Configuration Protocol – IP assignment (server) |
| 68 | UDP | DHCP | Dynamic Host Configuration Protocol – IP assignment (client) |
| 69 | UDP | TFTP | Trivial File Transfer Protocol |
| 80 | TCP | HTTP | Hypertext Transfer Protocol – web traffic |
| 110 | TCP | POP3 | Post Office Protocol v3 – email retrieval |
| 119 | TCP | NNTP | Network News Transfer Protocol |
| 123 | UDP | NTP | Network Time Protocol – time synchronization |
| 143 | TCP | IMAP | Internet Message Access Protocol – email retrieval |
| 161 | UDP | SNMP | Simple Network Management Protocol |
| 194 | TCP | IRC | Internet Relay Chat |
| 389 | TCP/UDP | LDAP | Lightweight Directory Access Protocol |
| 443 | TCP | HTTPS | HTTP Secure – encrypted web traffic (TLS/SSL) |
| 445 | TCP | SMB | Server Message Block – Windows file sharing |
| 465 | TCP | SMTPS | SMTP Secure – encrypted email sending |
| 514 | UDP | Syslog | System Logging Protocol |
| 587 | TCP | SMTP | SMTP submission – email sending with authentication |
| 636 | TCP | LDAPS | LDAP over SSL |
| 993 | TCP | IMAPS | IMAP Secure – encrypted email retrieval |
| 995 | TCP | POP3S | POP3 Secure – encrypted email retrieval |
| 1080 | TCP | SOCKS | SOCKS proxy protocol |
| 1194 | UDP | OpenVPN | OpenVPN default port |
| 1433 | TCP | MSSQL | Microsoft SQL Server |
| 1521 | TCP | Oracle | Oracle Database |
| 2049 | TCP/UDP | NFS | Network File System |
| 3000 | TCP | Dev Server | Common development server port (Node.js, etc.) |
| 3306 | TCP | MySQL | MySQL / MariaDB database |
| 3389 | TCP | RDP | Remote Desktop Protocol – Windows remote access |
| 4443 | TCP | HTTPS-alt | Alternate HTTPS port |
| 5000 | TCP | Dev Server | Common development server port (Flask, etc.) |
| 5432 | TCP | PostgreSQL | PostgreSQL database |
| 5900 | TCP | VNC | Virtual Network Computing – remote desktop |
| 6379 | TCP | Redis | Redis in-memory data store |
| 6443 | TCP | Kubernetes | Kubernetes API server |
| 8080 | TCP | HTTP-alt | HTTP alternative port – common for proxies and dev servers |
| 8443 | TCP | HTTPS-alt | HTTPS alternative port |
| 8888 | TCP | Jupyter | Jupyter Notebook default port |
| 9000 | TCP | PHP-FPM | PHP FastCGI Process Manager |
| 9090 | TCP | Prometheus | Prometheus monitoring server |
| 9200 | TCP | Elasticsearch | Elasticsearch REST API |
| 9300 | TCP | Elasticsearch | Elasticsearch cluster communication |
| 27017 | TCP | MongoDB | MongoDB document database |
| 27018 | TCP | MongoDB | MongoDB shard server |