OPNsense reliability architecture calculator
OPNsense Reliability & HA Calculator: Firewalls, WANs, UPS & Cooling
Reliability planning becomes useful when it reveals what can still fail, not when it produces a decorative uptime score. This calculator combines firewall count, WAN diversity, link speed, switching, protected electrical load, desired battery time, CARP intent, IDS/IPS and ambient temperature. It then highlights a practical hardware direction and the most obvious shared failure domains. The result is a design screen to guide shopping and testing, not a guarantee that the completed network will meet a particular availability percentage.
Quick answer
Count failure domains first, then size the surviving path
A two-node CARP design should leave one node capable of carrying the full workload, while a dual-WAN design should keep at least one usable provider path after the other fails. UPS sizing should cover every network device required for that surviving path. If the selected topology still has one switch, one ISP, one UPS or one hot cabinet shared by everything, the calculator calls that out instead of hiding it behind a high score.
Live Amazon hardware
Live hardware for reliability planning
The catalogue combines firewall appliances, UPS units, managed switches and internal SSDs so the architecture can be translated into real component options. Product availability and pricing are live where accepted catalogue records exist.
Buying decision
Use the result as a commissioning checklist, not a purchase verdict
The calculator can screen port count, power capacity, battery energy, cooling direction and storage tier, but it cannot know switch firmware, ISP restrictions, exact UPS runtime curves or whether pfSync is truly passing states. Treat every output as a hypothesis to verify on the actual hardware. The final architecture should survive the failure events that matter to the site and be simple enough that administrators can test and maintain it.
Interactive planner
OPNsense Reliability & HA Calculator
Combine firewall, WAN, switch, power, thermal and storage inputs into one reliability architecture screen.
The UPS result is an output and energy screen, not an exact runtime promise. The architecture result identifies obvious single points of failure but cannot prove that WAN circuits, switches or power feeds are truly independent.
Compatibility checkpoints
How to read the calculator output
Firewall topology
Two nodes make CARP possible, but both still need enough performance, ports and thermal margin to carry production alone.
Power screen
The calculator totals selected network loads, adds output margin and estimates usable battery energy; verify runtime on the exact UPS curve.
Cooling direction
Higher CPU/link/IDS load and warmer ambient conditions increase the case for active airflow or stronger thermal validation.
Reliability gaps
Any remaining single WAN or switch is reported as a failure domain rather than converted into a misleading numerical uptime score.
Start with the services that must remain reachable
List what outage actually means for the site: internet access, remote VPN, voice, cloud applications, local VLAN routing, DNS, cameras or management. Reliability hardware should preserve those services, not simply keep the firewall LEDs on. A network may need dual WAN but tolerate a brief firewall reboot, or it may need CARP because remote employees cannot wait for manual intervention. When the requirement is explicit, the calculator inputs become measurable design choices instead of a collection of maximum values chosen because bigger hardware appears safer.
Two firewall nodes remove only the firewall-node failure
CARP can move shared addresses when a primary node disappears, and pfSync can preserve many states, but the pair still relies on external infrastructure. The calculator therefore does not award an abstract HA score merely because node count is two. It also looks at switches and WAN paths, and the surrounding guide asks whether the power system and ISP handoffs are shared. This failure-domain approach is more useful than multiplying component reliability percentages that are unknown and highly dependent on configuration, maintenance and environment.
Size each node for the surviving workload
When one firewall is down for maintenance or failure, the remaining node should still support the selected WAN and LAN speeds plus IDS/IPS or VPN workload. The reliability calculator does not estimate exact packet throughput because that requires CPU, NIC and rule-set details from Sprint 5A, but it assumes the pair is not a load-sharing crutch. If a design needs both nodes active to meet normal performance, it has no capacity reserve when one disappears. Confirm individual-node throughput separately before treating CARP as production-ready.
Port count grows as redundancy grows
A small single-WAN firewall may need only WAN and LAN. Add a second WAN, multiple physical LAN trunks, dedicated management and pfSync and the interface requirement expands quickly. The calculator provides a basic per-node port direction for HA designs, while the detailed CARP and HA pages show why roles must remain consistent. If the appliance lacks enough native ports, a supported PCIe NIC can be cleaner than repurposing USB network adapters. Reserve at least one sensible expansion path so future redundancy does not require replacing the entire firewall.
WAN count should reflect real independence
Entering two WANs is meaningful only when they fail independently enough to meet the objective. Two logical services delivered over the same physical access network can still share a cable cut or provider fault. A fiber circuit plus 5G backup may have different failure modes but different latency and inbound capabilities. Document provider, physical entry, modem/ONT, public-address behavior and data limits. The calculator flags a single WAN as a reliability gap, but it is up to the deployment to verify that multiple WANs are more than two interfaces connected to the same risk.
Switch count is not the same as switch redundancy
Two switches improve resilience only if the cabling and VLAN design allows the active firewall and critical clients to remain connected after either device fails. If both switches depend on one power supply, one uplink or an untested stacking control plane, the practical independence may be lower than the count suggests. Use the calculator’s switch gap as a prompt for a topology review. Test each switch outage while watching CARP, MAC learning and client sessions so the physical wiring, trunk configuration and gateway design are proven together.
UPS capacity must cover the complete surviving network path
The calculator totals firewall, switch and modem/ONT watts based on the counts entered and adds conservative output and battery-energy headroom. This is useful for narrowing UPS classes, but exact battery runtime must come from the chosen model’s runtime curve at the measured load. Decide whether both redundant paths share one UPS or are split across power systems. A pair of firewalls on battery cannot provide service if the active switch or ISP handoff is plugged into an ordinary wall outlet that drops as soon as utility power fails.
Runtime targets should follow outage and shutdown strategy
Twenty minutes may be ideal in a site where most outages are brief and a generator starts quickly, while another location may need only enough battery time for graceful shutdown. Longer targets increase battery cost and physical size rapidly. Determine which network functions should remain alive throughout the outage and whether servers will shut down before the firewall. Use NUT or vendor signaling where supported, and test the low-battery workflow. The calculator’s watt-hour estimate helps compare architectures but should never be published as an exact model runtime.
Cooling is a reliability dependency, especially in multi-gig builds
A redundant pair placed in the same warm cabinet can share the same thermal failure mode. The calculator raises the cooling direction when faster links, IDS/IPS and warmer ambient conditions stack together. Use the detailed thermal guide to validate N100, N305 or Core-class appliances under sustained load. Spread passive chassis apart, avoid blocking fins and consider active airflow where needed. Monitor SSD and NIC heat as well as CPU temperature. Environmental redundancy is often overlooked because it does not appear in a conventional network diagram.
Storage should be sized for operations, not uptime theater
A 2TB NVMe does not make a firewall highly available. OPNsense currently gives 120GB SSD as a recommended general target, and Cloudzat’s larger planning tiers simply provide headroom for local logging, IDS events and analytics. Reliability comes from healthy free space, backups and a rebuild process more than raw capacity. If the firewall fails because of storage, administrators should be able to install OPNsense on a replacement drive and restore configuration without relying on files trapped on the failed device.
Configuration is a failure domain that hardware cannot duplicate away
A bad firewall rule, incorrect gateway group or broken HA synchronization can affect both nodes even when every component is healthy. Maintain off-device configuration backups and use a controlled primary-to-backup synchronization workflow. Current OPNsense HA guidance deliberately supports keeping the backup in a known-good state during maintenance. Include configuration review and rollback in the availability plan. A design with perfect hardware redundancy but no safe change process may experience more downtime from operator error than from component failure.
Commission the architecture with destructive but controlled tests
After installation, fail one component at a time: primary firewall, pfSync link, WAN1, WAN2, one switch and utility power where safe. Keep representative sessions active and observe CARP state, DNS, VPN, gateway monitoring, IDS/IPS and alerts. Restore components and test failback according to policy. Document expected behavior and recovery steps. Revisit the calculator after major changes such as adding 10GbE, enabling inspection or increasing PoE load, because the original capacity and thermal assumptions may no longer describe the network.
Questions people ask
OPNsense reliability calculator questions
Does this calculator predict uptime percentage?
No. It identifies hardware capacity and obvious failure domains. A credible uptime percentage would require failure-rate, repair-time, configuration and dependency data that the calculator does not have.
How many firewall nodes do I need for CARP?
A conventional automatic failover pair uses two nodes. Each should be able to carry the production workload alone and should have compatible interface assignments.
Why does the calculator flag one switch?
Because a single switch can disconnect both firewalls or critical clients even when CARP is configured correctly. Whether a second switch solves that depends on the actual VLAN and cabling design.
How is UPS size calculated?
It totals the selected network watt load, adds output headroom and estimates usable battery energy for the requested minutes. You must verify actual runtime against the exact UPS manufacturer curve.
Why include modem or ONT watts?
Internet failover cannot work during a local power outage if the provider handoff device loses power even while the firewalls remain on battery.
Does two WANs guarantee provider redundancy?
No. The circuits may share carrier infrastructure, building entry, upstream equipment or power. Verify actual path diversity.
How does IDS/IPS affect reliability planning?
It can increase sustained CPU load and heat. The surviving firewall must have enough performance and thermal margin to continue inspecting traffic during failover.
Why is storage part of the calculator?
Local logs and analytics need reliable free space, but storage is kept as a practical capacity tier rather than treated as the main determinant of firewall uptime.
Should both HA nodes share the same UPS?
They can in simpler deployments, but the UPS then remains a common failure domain. Higher-availability designs may justify separate power paths for nodes and supporting switches.
What should I do after using the calculator?
Translate the output into a physical diagram, verify exact product compatibility, and run controlled failover, WAN, switch, power and recovery tests on the production hardware.
Official references and methodology
Verify the live topology and hardware before deployment
Cloudzat intentionally avoids converting uncertain dependency and failure-rate data into an uptime percentage. The calculator screens capacity, port count, protected load, battery energy, cooling and obvious single points of failure, while official OPNsense documentation defines CARP, pfSync, multi-WAN and NUT behavior. Live hardware prices are used only when the dedicated catalogue has accepted current listings.
- OPNsense High Availability documentation
- OPNsense Configure CARP guide
- OPNsense Multi WAN guide
- OPNsense Network UPS Tools guide
- OPNsense hardware sizing documentation
As an Amazon Associate, Cloudzat may earn from qualifying purchases. Prices, firmware, UPS runtime, battery condition, NIC revisions, SSD variants, appliance configurations and seller terms can change. Verify the exact delivered hardware and current OPNsense documentation before production deployment.