CREST Practitioner Security Analyst (CPSA) Practice 2026 - Free CPSA Practice Questions and Study Guide

The correct identification of the protocol associated with port 18 is the Message Send Protocol (MSP). This protocol is primarily used for transmitting messages across a network, specifically in earlier networking environments. It has been largely overshadowed by more widely adopted messaging and communication protocols, but it historically served the purpose of facilitating communication between different machines on a network.

Port 18 is designated specifically for this protocol, making it important to understand that specific ports are often assigned to particular protocols as a means of differentiating network traffic. In the contemporary context, other protocols such as FTP (File Transfer Protocol) on port 21, HTTP (HyperText Transfer Protocol) on port 80, and Telnet on port 23 are better known for their respective uses, but they occupy different ports and serve different functions than MSP. This illustrates the unique assignment of port numbers in the organization of network communications and the historical context in which MSP was utilized.