SCADA Network Troubleshooting Checklist

Start with scope

Identify what changed, what is affected, and what still works. A single device failure, subnet failure, server failure, and firewall issue produce different evidence.

Layered checks

1. Physical link: power, link lights, cabling, media converters, switch ports.
2. IP layer: address, subnet mask, gateway, duplicate IPs, VLANs.
3. Reachability: ping when allowed, ARP table, route path.
4. Transport: TCP port availability with a known tool.
5. Protocol: unit ID, endpoint, namespace, topic, credentials, certificates.
6. Application: tag mapping, scan class, quality, permissions, logs.

Evidence to collect

• Device IP and firmware.
• Switch port and VLAN.
• Error counters and link speed.
• SCADA driver diagnostics.
• Packet capture when allowed.
• Time of failure and recent changes.

Practical rule

Prove the lowest failing layer before editing application configuration.