| 20 | TCP | FTP Data | File Transfer Protocol — data transfer channel |
| 21 | TCP | FTP Control | File Transfer Protocol — command/control channel |
| 22 | TCP | SSH | Secure Shell — encrypted remote login and command execution |
| 23 | TCP | Telnet | Unencrypted text-based remote terminal protocol (insecure) |
| 25 | TCP | SMTP | Simple Mail Transfer Protocol — email delivery between servers |
| 53 | Both | DNS | Domain Name System — hostname to IP resolution |
| 67 | UDP | DHCP Server | Dynamic Host Configuration Protocol — server side |
| 68 | UDP | DHCP Client | Dynamic Host Configuration Protocol — client side |
| 69 | UDP | TFTP | Trivial File Transfer Protocol — simple UDP-based file transfer |
| 80 | TCP | HTTP | Hypertext Transfer Protocol — unencrypted web traffic |
| 110 | TCP | POP3 | Post Office Protocol v3 — email retrieval (unencrypted) |
| 119 | TCP | NNTP | Network News Transfer Protocol — Usenet newsgroup articles |
| 123 | UDP | NTP | Network Time Protocol — clock synchronization |
| 143 | TCP | IMAP | Internet Message Access Protocol — email retrieval (unencrypted) |
| 161 | UDP | SNMP | Simple Network Management Protocol — network device monitoring |
| 162 | UDP | SNMP Trap | SNMP trap notifications from managed devices |
| 194 | TCP | IRC | Internet Relay Chat — real-time text messaging protocol |
| 389 | TCP | LDAP | Lightweight Directory Access Protocol — directory services |
| 443 | TCP | HTTPS | HTTP over TLS/SSL — encrypted web traffic |
| 445 | TCP | SMB | Server Message Block — Windows file and printer sharing |
| 465 | TCP | SMTPS | SMTP over TLS — secure email submission (legacy) |
| 514 | UDP | Syslog | System logging — network device log messages |
| 587 | TCP | SMTP Submission | Email submission with STARTTLS — modern preferred port |
| 636 | TCP | LDAPS | LDAP over SSL/TLS — secure directory access |
| 993 | TCP | IMAPS | IMAP over TLS/SSL — secure email retrieval |
| 995 | TCP | POP3S | POP3 over TLS/SSL — secure email retrieval |
| 1080 | TCP | SOCKS Proxy | SOCKS proxy protocol — routes network packets through proxy |
| 1194 | Both | OpenVPN | OpenVPN — open-source VPN solution |
| 1433 | TCP | MSSQL | Microsoft SQL Server database |
| 1521 | TCP | Oracle DB | Oracle database listener default port |
| 2181 | TCP | ZooKeeper | Apache ZooKeeper — distributed coordination service |
| 2375 | TCP | Docker | Docker daemon API (unencrypted — do not expose) |
| 2376 | TCP | Docker TLS | Docker daemon API over TLS |
| 3000 | TCP | Dev Server | Common development server port (Node.js, React, Grafana, etc.) |
| 3306 | TCP | MySQL | MySQL / MariaDB relational database server |
| 3389 | TCP | RDP | Remote Desktop Protocol — Windows remote desktop access |
| 4200 | TCP | Angular Dev | Angular CLI development server default port |
| 5000 | TCP | Flask / Dev | Common Flask development server / UPnP / various apps |
| 5432 | TCP | PostgreSQL | PostgreSQL relational database server |
| 5672 | TCP | RabbitMQ AMQP | RabbitMQ / AMQP message broker protocol |
| 5900 | TCP | VNC | Virtual Network Computing — remote desktop (RFB protocol) |
| 6379 | TCP | Redis | Redis in-memory data structure store / cache |
| 6443 | TCP | Kubernetes API | Kubernetes API server (kube-apiserver) |
| 8080 | TCP | HTTP Alt | Alternative HTTP port — proxy servers, app servers, dev |
| 8443 | TCP | HTTPS Alt | Alternative HTTPS port — commonly used by app servers |
| 8888 | TCP | Jupyter | Jupyter Notebook default port / various HTTP alt uses |
| 9092 | TCP | Kafka | Apache Kafka message broker |
| 9200 | TCP | Elasticsearch | Elasticsearch REST API (search and analytics) |
| 9300 | TCP | Elasticsearch Transport | Elasticsearch cluster inter-node communication |
| 15672 | TCP | RabbitMQ UI | RabbitMQ management web UI |
| 27017 | TCP | MongoDB | MongoDB document database default port |
| 27018 | TCP | MongoDB Shard | MongoDB shard server (mongod --shardsvr) |