Firewall vs. Data Diode TCO Calculator
Enter your environment parameters across three phases. The calculator identifies the exact month where the data diode's higher upfront cost is recovered by firewall OpEx savings — and produces a CFO-ready output you can take directly to a budget conversation.
How to use this tool
Work through the three phases in order. Defaults are populated based on typical OT environments — adjust them to match your situation. The comparison assumes one firewall and one diode pair per protected network segment. Scale using the segment count in Phase 1.
Phase 1
Environmental scale
Number of network segments requiring protection
Count the chokepoints where a firewall or diode would sit, not individual assets
Internal fully burdened labor rate
Include salary, benefits, and overhead
Projection horizon
Years of ownership to compare
Compliance requirements
Affects audit documentation savings calculation for diode scenario
Compliance mode adds estimated annual audit documentation hours to the firewall scenario (firewall rule sets require ongoing audit evidence) and subtracts hours saved from the diode scenario (diodes produce simpler, more defensible audit evidence).
Phase 2
Firewall scenario
Average hardware cost per firewall appliance
Industrial-grade NGFW; typical range $8,000–$25,000
Annual subscription fee per firewall
IPS/IDS, threat feeds, support; typically 20–30% of hardware cost annually
Average patch cycles per year
Major firmware updates requiring staging and validation; typically 2–4
Hours per patch cycle per firewall
Staging, vendor validation, plant maintenance window coordination
Annual rule audit and maintenance hours per firewall
Rule review, cleanup, change requests
Phase 3
Data diode scenario
Upfront hardware cost per diode pair / gateway
Including protocol replication appliance; typical range $20,000–$60,000
One-time engineering hours for protocol replication setup
Per diode pair; historian configuration, testing, validation
Annual hardware maintenance and support fee per diode
Vendor support contract; typically 10–15% of hardware cost
OpEx break-even crossover
Firewall scenario
CapEx (hardware)
Subscriptions
Patch labor
Rule maintenance labor
Total
Data diode scenario
CapEx (hardware + setup)
Annual maintenance
Total
CFO-Ready Results
OT Cybersecurity Software — otcybersecuritysoftware.com
Environment
Segments
Projection
Labor rate
Compliance
Break-even crossover
Firewall total
Data diode total
Generated by the Firewall vs. Data Diode TCO Calculator at otcybersecuritysoftware.com. Figures are estimates based on user-supplied inputs. This output is intended as a decision-support tool and does not substitute for vendor quotes or procurement review.
Related guide
The Firewalls vs. Data Diodes guide covers placement logic across the Purdue model, vendor landscape, common deployment mistakes, and how to frame the business case for a COO or CFO.