CREST Practitioner Security Analyst (CPSA) 2025 – 400 Free Practice Questions to Pass the Exam

The protocol that operates on Port 137 (UDP) is NetBIOS (name services). NetBIOS is a network protocol used for communication over a local area network, primarily for providing services related to file and printer sharing, as well as name resolution. Port 137 specifically handles the name service aspect of NetBIOS, which enables applications to communicate and identify each other on the network by name rather than IP address.

Understanding the role of NetBIOS in networking contexts helps clarify why it operates on this specific port. In contrast, Domain Name System (DNS) operates on different ports, typically 53, for resolving domain names to IP addresses. Telnet serves a different function entirely, allowing remote command-line access usually on port 23. Active Directory is a directory service by Microsoft that functions primarily over various protocols including LDAP, but it does not specifically operate on Port 137 for its basic services. Therefore, NetBIOS is the clear and relevant choice in this scenario concerning Port 137.