Help Desk Geek – How to Find Open and Blocked TCP/UDP Ports

netwrix – Handling Open Ports Secure and Finding Vulnerabilities

Environmental Protection Agency – Configuration Management Procedures

Georgetown University – Restricted List of Ports, Protocols, and/or Services

DoD Instruction 8551.01 – Ports, Protocols, and Services Management (PPSM)

NIST SP 800-53: CM-7 Least Functionality