Port 18
Message Send Protocol
Message Send Protocol (MSP) is a legacy protocol designed primarily for transmitting short, text-based notifications between networked hosts. It facilitates simple communication by enabling users or systems to send alerts or brief messages without the need for complex email or file transfer protocols. While it once played a role in system messaging and network administrative alerts, its use today has largely been deprecated due to the prevalence of more secure and feature-rich alternatives..
Technical Details
Introduction
Message Send Protocol (MSP) operates over TCP and UDP port 18. It was created to provide straightforward message delivery across interconnected hosts by transferring a simple text payload. Unlike email protocols that involve headers, attachments, and complex formatting, MSP sends short plaintext messages without additional structure.
Operation
The protocol works by establishing a connection (over TCP) or sending datagrams (over UDP) to a listening service on port 18. The client transmits the message content, which is either displayed to the user or processed by a local application. Since there is minimal overhead, MSP ensures low-latency delivery, suitable for brief alerts or status updates rather than long-form communication.
Deployment Context
Historically, MSP served system administrators as a network-based notification tool, integrated into Unix environments and early distributed systems to send concise updates about system states, service events, or critical network alerts. Its simplicity meant low resource consumption but at the cost of lacking encryption, authentication, or advanced delivery guarantees.