Building an OT Asset Inventory that Works: The Whys and How’s

In today’s threat-heavy operational landscape, industrial environments, from power plants to refineries, water treatment systems to smart factories, are increasingly connected, complex, and vulnerable. Amid this complexity, OT asset discovery and management has emerged as one of the most foundational components of operational technology (OT) cybersecurity.

Yet, in many industrial enterprises, asset discovery is either incomplete, static, or entirely missing. Without a real-time, accurate inventory of assets, it's virtually impossible to secure them. As cyber threats proliferate, from ransomware targeting PLCs to state-sponsored ICS espionage, this is no longer acceptable.

This article explores why OT asset discovery and management is critical, how OT operators and cybersecurity teams can approach it effectively and offers a practical checklist for implementation.

Why OT Asset Discovery and Management Matters

1. Cyber risk begins with what you don’t know

You can't protect what you can't see. Unknown or unmanaged assets, such as rogue engineering laptops, shadow PLCs, legacy Windows systems, or even vendor-installed backdoors, represent blind spots in your network. These often become entry points for attackers.

2. Enables effective Vulnerability Management

Many ICS components have known vulnerabilities (e.g., CVEs affecting Siemens S7 PLCs, GE DCS controllers, etc.). Asset discovery allows you to map vulnerabilities to specific assets, prioritize based on criticality, and plan patching or segmentation strategies accordingly.

3. Supports segmentation and network design

Knowing the role, behavior, and communication patterns of each asset helps define zones and conduits in accordance with IEC 62443. This is essential for isolating critical assets from the enterprise IT layer and reducing the attack surface.

4. Essential for Incident Response

During an incident, such as a malware outbreak or ransomware event, real-time asset data allows responders to contain, isolate, and remediate more effectively. It provides clarity on what’s at risk, what’s impacted, and what’s still operational.

5. Compliance and governance

Regulations like NIS2, CEA Guidelines (India), and IEC 62443 increasingly demand accurate asset inventories, vulnerability management, and documented controls. Discovery tools simplify compliance and reduce audit burden.

OT Asset Discovery vs IT Asset Discovery

Asset management in OT is entirely different from IT. Here's are some of the key differences:

Thus, OT asset discovery requires purpose-built tools and processes that align with the realities of ICS environments.

Key pillars of OT Asset Discovery and management

1. Passive network monitoring

Tools such as Nozomi Networks, Claroty, Dragos, or Cisco Cyber Vision passively monitor network traffic via SPAN ports or network taps. These tools:

· Identify assets based on ICS protocols (e.g., Modbus, DNP3, Profinet, EtherNet/IP)

· Map communication flows

· Detect changes in asset behavior

· Provide a live inventory

2. Active probing (Selective)

Used carefully and in limited scopes, active scanning helps detect dormant assets or fill in missing data fields (e.g., firmware version). However, this should never be run indiscriminately, and only during planned downtime or on test environments.

3. Integration with CMDB and ITAM

Discovered OT assets should feed into a central Configuration Management Database (CMDB) or Asset Management System (ITAM), with separate tagging for criticality, zone, and function.

4. Contextual Enrichment

It’s not enough to know “Device A is a PLC.” You need enriched metadata:

· Make, model, serial number

· Installed firmware version

· Running protocols

· Communication partners

· Engineering access status

This contextual detail enables vulnerability prioritization, maintenance planning, and change detection.

5. Lifecycle management

Asset management is not a one-time project. It requires:

· Continuous monitoring

· Change detection and validation

· Regular audits

· Decommission tracking

In mature OT environments, assets are tagged from procurement to retirement, including spares and staging systems.

Common Challenges in OT Asset Management

Best practices for OT Asset Discovery and Management

1. Start with a crown jewel analysis

Identify your most critical processes and systems. Prioritize visibility and monitoring for those assets first.

2. Deploy passive discovery tools early

Use passive monitoring using tools such as Shieldworkz as your foundational approach, this minimizes risk while maximizing visibility. Ensure that the tool is able to give a full list of assets with accuracy.  

3. Involve operators and maintenance

Operators often know legacy equipment better than anyone. Use their tribal knowledge to supplement discovery efforts, if required.

4. Don’t rely on spreadsheets or asset discovery vendors that push spreadsheets or manual asset identification

Implement an OT-specific Asset inventory platform such as Shieldworkz that supports:

· Real-time updates

· Visualization (topology maps)

· Vulnerability data integration

· User-defined tags and asset groups

· All details should be maintained in an automated manner  

Any OT security vendor that pushes for manual updating of asset inventories is not a mature or reliable vendor.

5. Define ownership

Clearly assign ownership for maintaining asset inventory accuracy in addition to operations. This could lie with the OT cybersecurity team or be embedded within reliability/maintenance.

OT asset management: Security use cases

OT asset discovery and management checklist

CISOs and security leaders can use the below checklist from an OT cybersecurity perspective:

Here is a structured checklist from an OT cybersecurity perspective:

A. Planning and scoping

· Define the complete scope in detail: plant-wide, zone-based, or critical system only

· List every OT protocols used (Modbus, DNP3, OPC-UA, etc.)

· Identify key stakeholders: OT operations, cybersecurity, OEMs

· Define criticality levels for assets (High, Medium, Low)

B. Tool deployment

Choose a passive discovery tool such as Shieldworkz with comprehensive ICS protocol support

Configure port mirroring (SPAN Port) or deploy TAPs without interrupting live systems

Validate tool findings with site engineers

C. Inventory building

One should ensure that the metadata includes:

· Asset type (PLC, RTU, HMI, IED)

· Vendor/make/model/Ver/other identifier

· Firmware version

· IP/MAC address

· Communication protocols

· Tag assets by zone/conduit (aligned to IEC 62443)

In addition, engineering access points and backdoor channels should be identified and noted

Create an initial asset topology map

D. Vulnerability and risk contextualization

· Integrate CVE databases or vendor advisories

· Map known vulnerabilities to assets

· Highlight end-of-life devices or unsupported firmware

· Prioritize vulnerabilities for remediation

· Identify attack paths that are open and close them  

Tag unpatched or exploitable devices for action

E. Ongoing management

· Schedule regular inventory audits

Set up alerts for:

· New devices on the network

· Configuration changes

· Unauthorized engineering access

· Devices turning offline

· Integrate with incident response playbooks at a device level

· Link inventory to CMDB or SOC visibility platform

F. Governance and compliance

· Maintain updated documentation of discovery methodology and findings

· Report asset inventory for regulatory compliance (e.g., NIS2, CEA)

· Define roles and responsibilities for inventory updates

· Ensure inventory supports OT cyber risk assessments

To conclude

In the world of OT cybersecurity, visibility is essential for security and for operations. Asset discovery and management is not just an IT hygiene task instead, it’s the backbone of all risk mitigation, resilience, and compliance initiatives in industrial control systems.

For OT operators, this is not optional, it’s existential and mandatory. An incomplete inventory today could easily turn into tomorrow’s breach vector. By embracing intelligent, passive discovery methods, deploying the right asset discovery and management solution like Shieldworkz and embedding asset management into daily OT workflows, industrial enterprises can finally start operating securely in a connected world.

If you have read this far, you definitely need to talk to us about how we can help you in your OT security journey specifically vis-à-vis OT asset management, OT security and OT risk assessment. Drop us a line here.