Software Secure Firewall Threat Defense
Platform Secure Firewall Threat Defense Virtual
Activity Onboard

Advanced Network Analysis and Preprocessing SCADA Preprocessors The Modbus Preprocessor

Last updated: Jul 29, 2025

The Modbus Preprocessor


 

This section applies to Snort 2 preprocessors. For information on Snort 3 inspectors, see https://www.cisco.com/go/snort3-inspectors.

The Modbus protocol, which was first published in 1979 by Modicon, is a widely used SCADA protocol. The Modbus preprocessor detects anomalies in Modbus traffic and decodes the Modbus protocol for processing by the rules engine, which uses Modbus keywords to access certain protocol fields.

A single configuration option allows you to modify the default setting for the port that the preprocessor inspects for Modbus traffic.