Common OPC Tunneling Issues & How to Fix Them

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OPC tunneling was designed to free industrial automation teams from the pain of DCOM – but it doesn’t mean connectivity problems disappear entirely. Engineers deploying OPC Classic communication across distributed or segmented networks frequently run into OPC tunneling issues that cause data loss, broken connections, and security gaps.

This guide covers the most common OPC tunneling issues, explains why they happen, and shows how to resolve them – including how OPCNet Broker® is built to eliminate them at the root.

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What is OPC tunneling and why does it matter?

OPC tunneling is a technique that replaces DCOM-based communication between OPC Classic clients and servers with a TCP/IP-based connection. Instead of relying on Windows DCOM – which requires complex configuration, opens a wide range of dynamic ports, and struggles across firewalls and WAN links – OPC tunneling encapsulates OPC data inside a standard, configurable TCP port.

The result is a simpler, more secure, and more reliable communication channel. However, even with a tunneling solution in place, specific configuration and network conditions can introduce their own set of challenges.

The most common OPC tunneling issues and how to fix them

1. DCOM errors and failed remote connections

DCOM remains the single biggest source of OPC Classic connectivity failures. When an OPC client tries to connect to a remote OPC server without a tunneling solution, it depends on DCOM for remote procedure calls. This triggers a cascade of potential problems: dynamic port allocation that firewalls block, authentication mismatches between Windows machines, and DCOM security permission errors that are notoriously difficult to diagnose.

The fix: Replace DCOM communication entirely using an OPC tunneling solution like OPCNet Broker®, which routes all OPC DA, HDA, and AE traffic through a single, configurable TCP port. This eliminates DCOM from the equation and makes firewall rules predictable and manageable.

2. Firewall and TCP port configuration problems

Even after deploying a tunneling solution, teams often encounter blocked connections due to firewall rules. OPC tunneling uses fixed TCP ports, but if those ports are not opened for bidirectional traffic – both inbound and outbound – the connection will fail silently or timeout.

The fix: Before deployment, verify that the TCP port assigned to your OPC tunneling solution is open for bidirectional communication on all firewalls and network security appliances between the client and server machines. OPCNet Broker® uses a single, user-configurable port, which makes this firewall rule straightforward to define and audit.

3. Connection drops and lack of automatic reconnection

Network micro-cuts, brief WAN interruptions, or infrastructure maintenance can drop an OPC tunneling connection. Without built-in reconnection logic, the OPC client loses its data subscription and the session must be manually re-established which in a 24/7 industrial environment is unacceptable.

The fix: Choose an OPC tunneling solution with automatic reconnection built in. OPCNet Broker® monitors the communication link continuously and automatically re-establishes the session after any interruption, without requiring operator intervention.

4. Data loss during network outages (no store & forward)

In environments with intermittent connectivity – remote sites, offshore platforms, or WAN-dependent networks – a temporary communication outage can mean process data is simply lost. If the tunneling solution has no store & forward capability, any data generated while the connection is down is gone.

The fix: Use a tunneling solution that buffers data locally during an outage and retransmits it in order once connectivity is restored. OPCNet Broker® includes store & forward functionality, ensuring data continuity even through extended network interruptions.

5. Security vulnerabilities from weak or absent encryption

OPC Classic was designed for closed networks and has no native encryption or authentication. When you tunnel OPC traffic across a wider network (or between IT and OT zone), transmitting it without encryption exposes process data and control commands to interception or tampering.

The fix: Ensure your OPC tunneling solution encrypts all traffic in transit. OPCNet Broker® provides data encryption without requiring certificates, combined with user authentication, IP whitelisting, and tag-level access control (browse, read, write permissions per user). This makes it suitable for secure IT/OT communication without the overhead of a PKI infrastructure.

6. OPC server redundancy gaps

Many industrial OPC servers are deployed with redundant installations to protect against hardware or software failure. However, most basic tunneling solutions have no awareness of redundancy. If the primary OPC server fails, the tunnel goes down and the client loses data until an operator manually switches to the backup server.

The fix: Use a tunneling solution with built-in redundancy management. OPCNet Broker® supports OPC server redundancy natively, automatically failing over to the backup server when the primary becomes unavailable, keeping your data pipeline intact without manual switching.

Best practices for deploying an OPC tunneling solution

Avoiding OPC tunneling issues starts before you install anything. Follow these practices for a smooth deployment:

Pre-installation checklist: Verify that OPC Core Components are correctly installed on both the client and server machines. Confirm network connectivity and document which TCP port your tunneling solution will use before touching firewall rules.

Deploy server-side first: Always complete the installation and configuration on the OPC server side before deploying on the client side. This ensures the server is ready to accept tunneled connections when the client comes online.

Phased rollout: In complex environments, start with a non-critical pilot area. Validate data flow, reconnection behavior, and security configuration before rolling out across the full network.

Monitor continuously: Set up monitoring for OPC communication health and network performance. Proactively catching a degraded link is far better than responding to a lost connection alert from operations.

Keep software updated: Regularly update OPCNet Broker®, Windows, and your antivirus software to ensure you benefit from the latest security patches and performance improvements.

How OPCNet Broker® resolves OPC tunneling issues end-to-end

OPCNet Broker® is a purpose-built OPC tunneling solution that addresses every category of OPC tunneling issue described above:

DCOM-free operation for OPC Classic DA, HDA, and AE
Single configurable TCP port – simplifies firewall rules
Automatic reconnection after network interruptions
Store & forward – no data loss during outages
Encryption without certificates, user authentication, IP whitelisting, and tag-level security
OPC server redundancy management – automatic failover, no manual switching

For organizations running OPC Classic in distributed, multi-site, or IT/OT-integrated environments, OPCNet Broker® removes both the complexity and the risk from OPC tunneling.

Download OPCNet Broker® and eliminate your OPC tunneling issues →

Also see: OPC Tunnelling Setup: Step-by-Step Guide Using OPCNet Broker® (No DCOM, 15 Minutes)