IEC 60870-5-104
A telecontrol protocol widely used by electric utilities in Europe and Asia, carrying IEC 60870-5-101 application data over TCP/IP on port 2404. It connects control centres to substations for SCADA monitoring and control, using an information-object model with cause-of-transmission codes and typed data points. Like its peers it has no authentication or encryption in its base form; IEC 62351 defines the security extensions. Often referred to simply as IEC-104.
Why It Matters
In practice IEC-104 is the European counterpart to DNP3 and carries the same class of risk: routable, unauthenticated, and directly attached to breaker and switch control. It is notable as the protocol used in the Industroyer/CrashOverride malware that caused a power outage in Ukraine in 2016, which included a dedicated IEC-104 module for issuing control commands — a reminder that OT protocol abuse is not theoretical and that attackers invest in protocol-specific tooling. Because command messages are structurally distinct from monitoring messages, single-command and double-command activation types are the events worth alerting on, and correlating them against operator intent is the practical detection. Controls are the familiar OT set rather than anything protocol-specific: segment the control centre from the substation network, restrict the conduit to known endpoints, and monitor passively. On exams such as ISA/IEC 62443 and OT security certifications, expect questions on IEC-104 as an unauthenticated control path and on the role of IEC 62351.
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Related Network Security terms
Firewall
A network security system that monitors and controls incoming and outgoing network traffic based on predetermined security rules, acting as a barrier between trusted internal networks and untrusted external networks. Firewalls can be hardware appliances, software applications, or cloud-based services. Types include packet-filtering, stateful inspection, application-layer (proxy), and next-generation firewalls (NGFW) that combine traditional filtering with intrusion prevention and deep packet inspection. Properly configured firewalls are the first line of defense in network security and are essential knowledge for Security+, CCNA Security, and CISSP certifications.
VPN (Virtual Private Network)
A technology that creates a secure, encrypted connection (tunnel) over a less secure network such as the internet, allowing remote users to access private network resources safely. VPNs use protocols like IPSec, SSL/TLS, WireGuard, or OpenVPN to encrypt data in transit. Common implementations include site-to-site VPNs connecting office networks and remote-access VPNs for individual users. Split tunneling allows users to route only corporate traffic through the VPN while personal traffic goes directly to the internet. VPN concepts are heavily tested in Security+, CISSP, and network security certifications.
IDS (Intrusion Detection System)
A device or software application that monitors a network or systems for malicious activity or policy violations and generates alerts when suspicious behavior is detected. IDS can be network-based (NIDS), monitoring traffic on network segments, or host-based (HIDS), monitoring activity on individual systems. Detection methods include signature-based (matching known attack patterns), anomaly-based (detecting deviations from normal behavior), and heuristic analysis. Unlike an IPS, an IDS only detects and alerts, it does not actively block threats. Popular IDS tools include Snort, Suricata, and OSSEC.
IPS (Intrusion Prevention System)
A network security tool that monitors network traffic flows to detect and actively prevent identified threats in real time. Unlike an IDS which only alerts, an IPS sits inline with traffic and can drop malicious packets, block connections, or reset sessions automatically. Modern IPS solutions use signature matching, anomaly detection, and behavioral analysis to identify attacks. They are often integrated into next-generation firewalls (NGFW) as a unified threat management feature. IPS is a key component of defense-in-depth strategies and is tested in Security+, CySA+, and CISSP certifications.
DMZ (Demilitarized Zone)
A physical or logical subnet that separates an internal network from untrusted external networks, providing an additional layer of security for public-facing services. Servers in the DMZ (such as web servers, email servers, and DNS servers) are accessible from the internet but isolated from the internal network by firewalls on both sides. If a DMZ server is compromised, the attacker still cannot directly reach internal resources. DMZ architecture is a classic example of defense-in-depth and network segmentation. It is a common topic in Security+, CISSP, and network architecture certifications.
SIEM (Security Information and Event Management)
A software solution that aggregates and analyzes security data from across the organization, including logs from firewalls, servers, endpoints, and applications, to detect threats and support incident response. SIEM platforms provide real-time alerting, correlation of events across multiple sources, dashboards, and compliance reporting. Leading SIEM tools include Splunk, Microsoft Sentinel, IBM QRadar, and Elastic Security. SIEM is the backbone of modern Security Operations Centers (SOCs) and is essential knowledge for CySA+, CISSP, and CISM certifications.