Redundancy is a crucial aspect of designing and configuring industrial control systems (ICS) to ensure high availability, fault tolerance and reliability. A redundant network architecture provides backup paths and redundant components that minimize downtime and limit single points of failure. This blog explores best practices for configuring a redundant network for an industrial control system and focuses on key considerations and steps to achieve a robust and resilient network infrastructure.

Redundant Network Topology Design

The first step in configuring a redundant network is to decide the network topology. Common topologies used in redundant networks are ring, star and mesh configurations. Each topology has its strengths and considerations, and the choice depends on the specific requirements of the industrial control system.

Ring Topology

• Ring Topology - A ring topology connects devices in a loop, where each device is connected to its neighboring devices. In case of a single link failure, data can still flow to all devices, ensuring uninterrupted communication. Ring topologies are suitable for systems that require fast recovery times and are often the most cost-effective redundant topology.

Star Topology

• Star Topology - A star topology connects devices to a central switch or hub. If one link fails, only the connected device is affected, while the rest of the network stays operational. Star topologies offer easy troubleshooting and scalability.
  
  
• A redundant star topology can be used in projects where the budget allows. In a redundant star topology, every link to the central switch or hub is duplicated, often with a redundant pair of core switches and redundant edge network switches.

Mesh Topology

• Mesh Topology - A mesh topology provides multiple redundant paths between devices, ensuring high fault tolerance. Implementing a fully meshed network can be complex and costly and often requires special hardware, so it is typically reserved for critical systems.

Redundant Network Components

To achieve redundancy, it is essential to deploy redundant network components throughout the infrastructure. Consider the following key components:

• Redundant Switches: Use multiple switches in a redundant network to eliminate single points of failure. Implement Spanning Tree Protocol (STP) or Rapid Spanning Tree Protocol (RSTP) to manage redundant paths and prevent bridge loops.
• Redundant Links: Establish redundant links between devices by connecting them to multiple switches or using link aggregation techniques such as Ethernet Link Aggregation Control Protocol (LACP) or Cisco's Port Aggregation Protocol (PAgP).
• Redundant Power Supplies: Equip critical devices with redundant power supplies or backup power sources, such as uninterruptible power supplies (UPS), to ensure continuous operation during power outages.

Network Segmentation and VLANs

Segmenting the network into separate VLANs (Virtual Local Area Networks) helps isolate traffic, improve network performance and enhance security. It is advisable to create separate VLANs for distinct types of traffic, such as control traffic, SCADA traffic, database traffic and management traffic. By logically separating traffic, one can control access, implement security measures and prioritize critical control traffic.

Spanning Tree Protocol (STP) Optimization

Spanning Tree Protocol (STP) is a fundamental protocol for bridge loop prevention in redundant networks. Default ST{ configurations may result in slow convergence times. Optimize the STP configuration by enabling Rapid Spanning Tree Protocol (RSTP) or Multiple Spanning Tree Protocol (MSTP), which offer faster convergence and better load balancing capabilities.

Network Monitoring and Management

Implement comprehensive network monitoring and management tools to proactively monitor the network's health and quickly identify any potential issues. Network management tools must provide real-time visibility, alerting capabilities, performance monitoring and historical data analysis. This ensures that network administrators can promptly address any network failures or performance degradation.

Out-of-band network management allows administrators to manage a network even if the network is down. This allows for a control traffic network and SCADA traffic network to effectively enable full administrative control of each other’s switches without the risk of losing remote connection to those switches in the field.

Testing and Maintenance

Regular testing and maintenance are crucial to ensuring the effectiveness of a redundant network. Conduct periodic failover tests to verify that the redundant paths and components function as expected. Additionally, keep the network infrastructure up to date with the latest firmware updates and security patches to mitigate potential vulnerabilities.

Conclusion

Configuring a redundant network for an industrial control system is essential to ensure high availability, fault tolerance and reliability. By carefully designing the network topology, deploying redundant components, implementing VLANs, optimizing spanning tree protocols and adopting robust monitoring and maintenance practices, industrial organizations can create a resilient network infrastructure. A properly configured redundant network minimizes downtime, enhances system performance and safeguards critical industrial control processes, thereby ensuring continuous operations and protecting against costly disruptions.

About the Author

Jason Barry is a Senior Controls Engineer for Hallam-ICS. He has spent his career working on process automation systems in a variety of industries including Semiconductor, Chemical, Food and Beverage, Oil and Gas, and Toxic Gas Monitoring. His area of expertise includes Rockwell PLCs, multiple SCADA software, and SQL databases.

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About Hallam-ICS

Hallam-ICS is an engineering and automation company that designs MEP systems for facilities and plants, engineers control and automation solutions, and ensures safety and regulatory compliance through arc flash studies, commissioning, and validation. Our offices are located in Massachusetts, Connecticut, New York, Vermont and North Carolina  Texas, Florida and our projects take us world-wide.