One of the most common and simplest communication protocol in ICS, originally developed in 1979 for Modicon PLCs (now Schneider Electric). Modbus is used for transmitting data between devices; it’s a request-response (master/slave) protocol. There are two main flavors: Modbus RTU (runs over serial lines like RS-485) and Modbus TCP (runs over TCP/IP networks). It’s considered a de facto standard because so many vendors implemented it and it’s openly published. However, Modbus has no built-in security (no encryption or authentication), which means it’s easy to use and integrate, but also easy to snoop or spoof.
