Tips for switching between multiple network segments of industrial control computers

Multi-Subnet Network Switching Techniques for Industrial Control Computers

Industrial control computers (ICCs) often operate across multiple subnets to manage distributed automation systems. Efficient network switching ensures seamless communication between devices on different network segments. This guide outlines practical techniques for achieving reliable multi-subnet connectivity in industrial environments.

Configuring Multiple IP Addresses on a Single NIC

A straightforward method for multi-subnet access involves assigning multiple IP addresses to a single network interface card (NIC). This approach eliminates the need for physical network changes while enabling communication with devices across subnets.

Implementation Steps

1. Access Network Settings: Navigate to the NIC properties in the operating system’s network configuration panel (e.g., Windows’ "Network and Sharing Center" or Linux’s "NetworkManager").

2. Open TCP/IP Configuration: Locate the "Internet Protocol Version 4 (TCP/IPv4)" settings and click "Advanced."

3. Add Secondary IPs: In the "Advanced TCP/IP Settings" window, under the "IP Settings" tab, click "Add" to input additional IP addresses and subnet masks for each target subnet.

4. Configure Default Gateways: Assign specific default gateways for each subnet or prioritize them using the "Metric" value (lower numbers indicate higher priority).

Example: An ICC managing PLCs on both 192.168.1.0/24 and 192.168.2.0/24 subnets can be configured with IPs 192.168.1.100 and 192.168.2.100, respectively.

Practical Considerations

• Subnet Mask Accuracy: Ensure subnet masks align with the network architecture to avoid routing conflicts.

• Gateway Prioritization: Use metrics to control traffic flow, ensuring critical communications use the optimal path.

• Testing: Verify connectivity to each subnet using tools like ping or tracert to confirm proper routing.

Routing Table Adjustments for Cross-Subnet Communication

When ICCs require communication across subnets separated by routers, manual routing table adjustments can direct traffic efficiently without altering device IPs.

Using the route Command (Windows/Linux)

1. View Existing Routes: Run route print (Windows) or netstat -rn (Linux) to inspect current routing entries.

2. Add Static Routes: Use commands like:

• Windows: route add -p 192.168.2.0 mask 255.255.255.0 192.168.1.1
  (Routes traffic to 192.168.2.0/24 via gateway 192.168.1.1)

• Linux: ip route add 192.168.2.0/24 via 192.168.1.1

3. Verify Routes: Confirm additions with route print or ip route show.

Scenario: An ICC on 192.168.1.0/24 needs to access a sensor on 192.168.3.0/24. Adding a static route via the intermediate router (192.168.1.254) enables direct communication.

Persistent Routing

• Windows: The -p flag in the route add command makes entries persistent across reboots.

• Linux: Edit /etc/network/interfaces or use netplan (Ubuntu) to save routes permanently.

Leveraging NAT and Gateway Devices for Subnet Isolation

Network Address Translation (NAT) and industrial gateways provide scalable solutions for managing multi-subnet environments, particularly in complex factory settings.

NAT for Subnet Unification

NAT devices translate IP addresses between subnets, enabling devices with overlapping or incompatible IPs to communicate.

• Implementation: Deploy a NAT gateway between subnets. Configure rules to map source/destination IPs and ports.

• Example: An ICC on 10.0.0.0/24 can access a PLC on 192.168.1.0/24 via NAT rules translating 10.0.0.10 → 192.168.1.20.

Industrial Gateway Features

• Protocol Conversion: Translate between industrial protocols (e.g., Modbus TCP to Profinet).

• Firewall Integration: Restrict traffic to authorized devices and ports.

• Logging: Monitor cross-subnet communications for troubleshooting.

Use Case: A manufacturing plant uses a gateway to unify PLC networks across production lines, enabling centralized monitoring without reconfiguring device IPs.

Security and Performance Optimization

Multi-subnet switching introduces security risks and potential performance bottlenecks. Mitigate these through:

• Access Control Lists (ACLs): Restrict traffic at routers/gateways to permit only essential communications.

• Quality of Service (QoS): Prioritize real-time control traffic (e.g., PLC commands) over non-critical data.

• Regular Audits: Review routing tables and firewall rules to remove obsolete entries.

Best Practice: Segment sensitive devices (e.g., HMI panels) into dedicated subnets with strict ACLs to minimize exposure to cyber threats.

By implementing these techniques, industrial operators can achieve reliable multi-subnet network switching, enhancing flexibility and efficiency in automation systems.