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Modbus Protocol
Port 502 is primarily associated with Modbus, a widely used industrial automation protocol. It facilitates communication between supervisory computers, controllers, and field devices like PLCs over TCP/IP networks..
Modbus is a communication protocol originally developed by Modicon in 1979 for use with programmable logic controllers (PLCs). It enables client-server communication between devices on industrial networks, allowing for monitoring and control of automation equipment. Modbus over TCP/IP (commonly referred to as Modbus TCP) standardizes this communication on modern Ethernet networks and predominantly uses port 502.
Port 502 serves as the default listening port for Modbus TCP servers (slaves). The protocol supports simple request-response messaging, making it straightforward to implement but lacking in complexity. It’s often favored in distributed control systems and SCADA (Supervisory Control and Data Acquisition) environments due to its openness and simplicity.
Besides TCP, Modbus can also operate over UDP for applications requiring lower overhead or less reliability, though TCP remains more prevalent. The protocol does not inherently support encryption or strong authentication, relying instead on network architecture segmentation and external protections.