The Reliability Impact of Cybersecurity Controls: Reconciling Security and Uptime in Industrial Networks

For CISOs, IT directors, network engineers, and operations teams charged with safeguarding critical infrastructures, the interplay between cybersecurity and system reliability is a recurring battleground. The persistent myth that robust security inevitably undermines reliability—fueling resistance to change among operational technology (OT) operators—continues to influence architecture and strategy. Let’s disentangle myth from reality, grounding our discussion in historical context, practical deployment insights, and the evolving demands of modern OT/IT collaboration.

Understanding the Core Tension: Security vs. Reliability

Security and reliability share a complex relationship: both aim to ensure trustworthy system operation, but the methods by which they do so can appear, at first glance, to be at cross purposes. Traditionally, OT engineers prioritized uptime and deterministic behavior, treating security controls as potential sources of unpredictable downtime. Meanwhile, IT teams, trained on “security by default,” introduce rigorous controls that could, if poorly implemented, increase operational risk through misconfiguration, latency, or outright denial of critical functions.

Historical Overview: Segmentation as an Original Control

Let’s step back: for decades, the primary “security” control in industrial environments was network segmentation. Air gaps—literal and logical—were considered sufficient to prevent external threats. Reliability was often achieved by isolating systems so thoroughly that even beneficial updates or monitoring were logistically difficult.

This changed in the late 1990s and early 2000s as:

• Control networks became TCP/IP based (see the emergence of Modbus TCP, EtherNet/IP, PROFINET)

• Remote maintenance needs, and data-driven initiatives (predictive maintenance, real-time analytics), put pressure on the siloed “air-gap” dogma

• Stuxnet (2010) shattered the illusion of absolute isolation

Reliability was no longer solely a product of physical separation but required consideration of logical and administrative boundaries. The challenge: how to enforce cybersecurity without undermining the deterministic behavior and uptime cherished in OT?

Deconstructing Key Cybersecurity Controls and Their Reliability Impacts

Network Firewalls & Segmentation

Positive impacts: Well-architected firewall policies and segmented VLANs reduce lateral movement and limit the blast radius of an incident. This actually supports reliability by containing faults—if a PLC is compromised, segmentation reduces the risk of cascading failures across the network.

Pitfalls: Mistuned or misconfigured firewalls can block critical traffic, causing “failures by policy.” In OT, lack of understanding about required protocols—such as multicast traffic or proprietary industrial automation control system (IACS) protocols—can cause outages. For example:

• Blocking UDP broadcast traffic may prevent device discovery on SCADA systems

• Too-severe east-west controls might break distributed control loops, leading to process instability

Intrusion Detection and Prevention Systems (IDS/IPS)

Value: Passive intrusion detection has minimal impact on uptime but significantly boosts the ability to detect subtle attacks targeting process integrity. A 2017 SANS report documented early detection as a leading factor in averting major outages from security incidents.

Caveat: Inline IPS introduces latency and, under heavy attack, can drop legitimate packets. In time-sensitive networks (TSN) or with legacy equipment intolerant of jitter, this can degrade operational performance or even induce unexpected fail-safes. Therefore, most mature industrial deployments opt for out-of-band IDS with periodic tuning, rather than default-to-block IPS strategies.

Authentication, Authorization, and Access Control

Historical context: “Everyone was admin” is not a joke in OT; default and shared accounts lingered due to operational convenience. The post-Target breach era (after 2013) made password policies and account management unavoidable (NERC CIP, IEC 62443 enforcement/encouragement).

Impact: Strong authentication (LDAP/Active Directory integration, multi-factor authentication) generally improves reliability by shrinking the attack surface of privileged access. However, poorly planned “lockdown” access controls can block maintenance staff at exactly the moment troubleshooting is most urgent. Solutions:

• Role-based access aligned with job functions, supported by robust redundancy in credential recovery

• Offline “break glass” mechanisms for barebones emergency access, with rigorous forensic auditing

Patch Management in OT

Principle: While unpatched vulnerabilities are a reliability liability (think: ransomware in process lines, as with the 2017 NotPetya incident), sudden, poorly coordinated patch cycles have historically crashed systems through incompatibility or triggering latent software bugs (the infamous Windows XP patching debacles in older HMI systems).

Better practice: Adaptive risk-based patching, leveraging test beds, legacy asset inventories, and tight vendor consultation. “Patching at the speed of OT” isn’t a slogan, it’s an operational necessity.

Architectural Patterns Reconciling Security and Reliability

Demilitarized Zones (DMZs) and Data Diodes

A classic architecture for balancing security and uptime is the controlled DMZ—buffer zones using dual firewall layers between IT and OT. Data diodes (unidirectional gateways) further guarantee high-reliability for data export while preventing inbound attack vectors. Historically pioneered in defense and nuclear sectors, these controls are now creeping into energy, water, and even food & beverage for their guarantee of both process integrity and forensic visibility.

Redundancy, Diversity, and Failsafe Design

The best security controls are designed with MTTR (Mean Time To Repair) and MBCF (Mean Between Control Failures) in mind. For industrial networking, dual-homed firewalls, redundant switches, and resilient access administration are gold standards. Overlay network designs (e.g., ring topologies with Rapid Spanning Tree Protocol, or parallel routed paths with VRRP/HSRP) ensure that single control failures don’t become operational showstoppers.

IT/OT Convergence: Decoding Collaborative Governance

The depth of misunderstanding between IT and OT teams is often underestimated. OT operators may regard security controls as intrusions on their realm, while IT professionals can misjudge the operational risks of enforcement, e.g., rebooting a PLC patch in the middle of a batch process. Bridging this gap is fundamentally about:

• Joint risk assessments: mapping out process-critical assets and potential business impacts

• Co-developed runbooks: incident response plans adapted for physical process safety requirements

• Regular, open communication—because an unspoken assumption is a potential source of downtime

Modern Connectivity Scenarios: Remote Access, Cloud, and Zero Trust

Remote Access (RDP, VPN, BeyondCorp Approaches)

COVID-19 stressed remote maintenance, leading to rampant “temporary” solutions that remain years later. The challenge: securing access while avoiding single points of failure. Split-tunnel VPNs, exposed RDP, and shadow IT increase the reliability risk profile. Properly designed remote access uses:

• Jump hosts with well-defined inbound/outbound ACLs

• Multi-factor authentication and session logging

• Time-bound, approval-based “just-in-time” access provisioning (see the evolution of privileged access management platforms)

Cloud Integration and Secure Data Flow

Data needs to flow between process networks and cloud platforms for analytics and digital twins. That path must be designed for both reliability (guaranteed delivery, lossless failover) and security (encryption, integrity checks). Message queueing (MQTT with TLS), secure APIs, and reverse-proxy architectures are now industry standards. The reliability risk lies mostly in poorly handled certificate management and over-complex API gateways; the lesson of recent outages is: simple, explicit architectures with monitored fallback modes consistently beat fragile “seamless” integrations.

Zero Trust: Theory and Practice in Industrial Settings

While “zero trust” is often more of a philosophy than a product, key elements—least-privilege access, continuous verification, explicit micro-segmentation—when implemented pragmatically, tend to raise both security and reliability by making lateral movement harder and failure domains smaller. Initial industry pilots (especially in oil/gas and pharmaceuticals) show up-front investment pays off against major incident downtime, though the complexity of migration (think: mapping old asset inventories!) cannot be overstated.

Concluding Perspectives: Honest Trade-offs in the Real World

No security control is free—it will always introduce new potential points of failure. The answer is not to avoid deploying controls, but to design, validate, and operate them collaboratively, with explicit focus on the reality of your unique industrial systems. Hybrid governance, operationally validated runbooks, and risk-based change management enable you to have both reliability and security—while the old “security vs. uptime” binary is increasingly a relic of the past.

What You Should Do Next

• Inventory critical process functions and map them to their supporting network and security controls

• Test and tune policies collaboratively, including “what if” scenarios where controls fail

• Insist on transparent root cause analysis for every incident—whether reliability or security—so both IT and OT teams learn, improve, and trust each other’s intent and expertise

Security and reliability are both trust problems—solve for one, and you’ll often improve the other, if you’re honest about your environment’s risks and needs.