DCOM

DCOM (Distributed Component Object Model) is a Microsoft technology for communication between software components across networks. Within OT and Industrial Automation, DCOM was used for years as the underlying communication layer for OPC DA systems, industrial data exchange and integration between SCADA, HMI, historians and PLC environments.

DCOM extends the local COM model so that software objects on different systems CAN communicate with each other as if they were running locally. This allowed industrial applications to exchange data in a vendor-neutral way within Windows-based OT networks.

Although DCOM played an important role historically within Industrial Automation, the technology is today known for complex management, Firewall problems, Security challenges and limited scalability. Within modern IT OT Convergence architectures, DCOM is therefore being replaced more often by protocols such as OPC UA, MQTT and web-based API architectures.

⚙️ What is DCOM

DCOM stands for:

Distributed Component Object Model

It is an extension of Microsoft COM (Component Object Model).

COM

COM provides communication between software components on the same system.

DCOM

DCOM enables communication between systems across a network.

Architecture:

Application
     │
COM Object
     │
   DCOM
     │
   Network
     │
Remote COM Object

Within industrial automation, DCOM is mainly associated with OPC DA.

🏗️ DCOM architecture

DCOM uses a client/server model.

Important components:

Communication runs via Microsoft RPC mechanisms.

📡 How DCOM works

When an application connects to a remote COM object:

1. Client requests an object reference
2. RPC Endpoint Mapper determines the port
3. Authentication is performed
4. Sessions are established
5. Data exchange starts

DCOM abstracts network communication so that applications appear to communicate locally.

🔌 DCOM within OPC DA

DCOM was widely applied as the transport layer for OPC DA.

Typical architecture:

PLC
 │
OPC Server
 │
DCOM
 │
SCADA Client

This allowed:

• SCADA systems
• historians
• engineering tools
• HMIs

to retrieve process data from OPC servers.

🧠 Why DCOM became popular

In the 1990s DCOM offered important benefits:

Because Windows was dominant within industrial software, DCOM rapidly grew into a standard technology.

⚡ Communication and ports

DCOM uses multiple network components.

RPC Endpoint Mapper

Standard usage:

TCP 135

After that, dynamic ports are assigned.

Issues:

• dynamic ports are hard to manage
• firewalls become complex
• Network Segmentation becomes harder

Within OT networks, this often led to operational problems.

🔒 DCOM security model

DCOM contains its own security model.

Important components:

Authentication usually uses:

• Windows accounts
• Active Directory
• NTLM
• Kerberos

⚠️ Why DCOM became problematic

DCOM was designed in a time when industrial networks were largely isolated.

Modern OT environments place much higher demands on:

• Cybersecurity
• segmentation
• firewall management
• scalability
• cloud integration

This led to important limitations.

🧱 Firewall issues

One of the biggest issues with DCOM is dynamic port allocation.

Issues:

Within strictly segmented OT networks, this often causes operational disruption.

🔓 Cybersecurity risks

DCOM introduces significant security risks.

Important threats

Historically, multiple vulnerabilities have been discovered within:

• RPC services
• COM objects
• Windows authentication
• OPC DA integrations

🛡️ Hardening of DCOM

Important security measures:

• limiting RPC port ranges
• Network Segmentation
• Industrial Firewall
• minimal privileges
• dedicated service accounts
• RPC filtering
• DCOM hardening policies
• Logging
• Security Monitoring

In addition, the following are often used:

• dedicated OPC gateways
• DMZ architectures
• protocol tunneling

🖥️ DCOM within OT networks

Within classic industrial networks, multiple DCOM components often ran:

SCADA
 │
OPC Client
 │
DCOM
 │
OPC Server
 │
PLC

Many legacy OT systems still depend on this architecture.

☁️ DCOM and IT/OT convergence

DCOM fits poorly within modern cloud and edge architectures.

Important limitations:

Modern OT platforms therefore shift towards:

• OPC UA
• MQTT
• REST APIs
• web services

🔄 OPC tunneling

To avoid DCOM problems, OPC tunneling solutions are often used.

Operation:

OPC Client
     │
Tunnel Software
     │
TCP Tunnel
     │
Tunnel Software
     │
OPC Server

Benefits:

• more firewall-friendly
• more stable connections
• less DCOM configuration
• better WAN support

📡 DCOM versus OPC UA

OPC UA was developed in part to solve DCOM problems.

Industrial automation is therefore shifting more towards OPC UA.

⚡ Performance considerations

Benefits

Drawbacks

For WAN connections, DCOM is often unsuitable.

🧪 DCOM in OT labs and legacy environments

DCOM remains relevant within:

• legacy SCADA
• old OPC servers
• existing Historian environments
• simulation systems
• OT labs

Many organisations cannot phase out DCOM directly because of:

• vendor lock-in
• old PLCs
• validation requirements
• production continuity

🏭 Practical applications

Manufacturing

Historically used for:

• machine monitoring
• SCADA integration
• historian collection

Energy supply

Use within:

• turbine monitoring
• substations
• EMS systems

Water sector

Applications:

• pumping stations
• remote Telemetry
• process visualisation

Building Automation

Integration of:

• HVAC
• energy management
• building monitoring

🛠️ Migration strategies

Many organisations gradually migrate away from DCOM.

Common strategies:

Migration is often complex because of dependencies within OT processes.

🛡️ Relevant standards and guidelines

Legacy DCOM environments increasingly fall under stricter Compliance requirements.

📈 Trends and developments

Important trends:

• phasing out DCOM
• migration to OPC UA
• protocol abstraction
• edge gateways
• MQTT integration
• Unified Namespace
• cloud-native OT

Despite ageing, DCOM will remain present for years to come within industrial legacy environments.

🎯 Conclusion

DCOM provided the technical basis for industrial interoperability within Windows-based OT environments for many years and played a crucial role in the rise of OPC DA.

Today, limitations around firewall management, cybersecurity, platform dependency and scalability mean DCOM is increasingly unsuitable for modern industrial networks.

Within IT OT Convergence architectures, the industry is therefore shifting towards more modern protocols such as OPC UA and MQTT, while DCOM remains an important part of many existing OT infrastructures for the time being.