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Australia, the United States, the UK and Canada jointly released a critical infrastructure guide detailing steps to successfully isolate vital operational technology (OT) and enabling systems from all other networks. With this capability, OT owners, operators and cyber defenders can provide continuity of their critical services in instances of crisis or service disruption. In the event of a…
Analysis Summary
# Best Practices: Operational Technology (OT) Isolation & Continuity
## Overview
These practices address the critical need for "manual" or "isolated" operating modes for Operational Technology (OT) within critical infrastructure. The goal is to ensure that vital services (water, energy, transportation) can continue to function independently even when IT networks, supply chains, or external communications are compromised or intentionally severed during a cyber incident.
## Key Recommendations
### Immediate Actions
1. **Comprehensive Asset Inventory:** Identify every device, sensor, and controller within the OT environment.
2. **External Connection Mapping:** Document all paths between the OT network and external networks (IT business systems, vendor remote access, and cellular gateways).
3. **Define the "Island Mode" Trigger:** Establish clear criteria for when the OT environment should be physically or logically disconnected from the corporate network.
### Short-term Improvements (1-3 months)
1. **Establish Hard Separation Points:** Install hardware-based disconnects or strictly configured firewalls at the OT/IT boundary to facilitate rapid isolation.
2. **Local Functional Persistence:** Ensure that local Human Machine Interfaces (HMIs) and controllers have the necessary logic and data to run without a connection to centralized enterprise servers.
3. **Manual Override Validation:** Physically test the ability to operate machinery and processes using manual controls without reliance on digital networking.
### Long-term Strategy (3+ months)
1. **Architecture Redesign:** Transition toward a "Zero Trust" OT architecture where the default state is minimal connectivity.
2. **Continuity of Operations Planning (COOP):** Develop and exercise "long-term independent operation" scenarios where the facility must run for weeks without external digital support.
3. **Supply Chain Decoupling:** Minimize dependence on cloud-based OT management tools that require constant internet "heartbeats" to function.
## Implementation Guidance
### For Small Organizations
* **Focus on Documentation:** Create "analog" binders containing network diagrams and manual operating procedures.
* **Physical Air-gapping:** Where hardware budgets are limited, use physical cable disconnection as a primary isolation strategy during crises.
### For Medium Organizations
* **Segmented VLANs:** Implement strict VLAN tagging and firewall rules to separate "Vital OT" from "Non-Essential OT" (e.g., HVAC or security cameras).
* **Redundant Local Storage:** Ensure historical data and operational logs are stored locally on-site, not just in the cloud.
### For Large Enterprises
* **Automated Kill-Switches:** Implement software-defined networking (SDN) that can trigger "Isolation Mode" across multiple sites simultaneously.
* **Dedicated OT SOC:** Establish a specialized security operations center focused solely on OT telemetry, independent of the corporate IT SOC.
## Configuration Examples
* **Firewall "Emergency Rule":** Configure a pre-staged firewall policy that blocks all Inbound/Outbound traffic to the IT subnet while allowing local Modbus/DNP3 traffic between PLCs and local HMIs.
* **Local Account Persistence:** Ensure OT administrative accounts are managed via a local database or local Active Directory instance that does not require a connection to the corporate domain controller to authenticate.
## Compliance Alignment
* **NIST SP 800-82:** Guide to Industrial Control Systems (ICS) Security.
* **ISA/IEC 62443:** International standards for the security of IACS.
* **CISA Cross-Sector Cybersecurity Performance Goals (CPGs):** Specifically the goals related to "Segmentation" and "Recovery."
## Common Pitfalls to Avoid
* **"Invisible" Dependencies:** Failing to realize that local OT systems rely on external DNS or NTP (time) servers located on the IT network.
* **Maintenance Backdoors:** Forgetting about cellular modems installed by vendors for "easy maintenance" that bypass isolation protocols.
* **Lack of Training:** Having an isolation plan that staff has never practiced, leading to panic or incorrect manual configurations during an actual event.
## Resources
* **CISA/IC3 Critical Infrastructure Guide:** `ic3[.]gov/CSA/2026/260728.pdf`
* **NIST Smart Connected Systems Division:** `nist[.]gov/el/smart-connected-systems-division`
* **CISA OT Security Resources:** `cisa[.]gov/operational-technology-video-series`