Firewall Mini PC Performance: Routing, VPN & IDS/IPS Explained

Quick Answer

Firewall mini PC performance is determined by the workload, not by Ethernet port speed alone. Basic routing and NAT are comparatively light. VPN encryption, traffic shaping, large state tables and IDS/IPS add CPU, memory and packet-processing overhead. A 10GbE port can negotiate a 10GbE link while the firewall itself delivers much less throughput once inspection or encryption is enabled.

The correct way to size a firewall is to define the traffic path, the packet mix and the services that must run at the same time. CPU architecture, NIC quality, memory, PCIe bandwidth and software configuration all matter.

Key Takeaways

· Link rate and firewall throughput are different metrics.

· Routing/NAT usually needs less compute than VPN or IDS/IPS.

· Small packets create more packets-per-second work than the same bandwidth carried in large packets.

· Good NICs reduce CPU overhead and improve consistency.

· VPN performance depends heavily on protocol, cipher and CPU acceleration.

· IDS/IPS must inspect traffic and can become the dominant CPU and memory workload.

· Benchmark results are only useful when packet size, rules, features and test direction are stated.

Start With the Traffic Path

Before comparing CPUs, draw the path a packet takes. Internet traffic may enter WAN, pass through NAT and filtering, then exit LAN. Inter-VLAN traffic may remain entirely inside the local network but still cross the firewall at Layer 3. A 1Gbps WAN does not prevent the firewall from seeing several gigabits of internal routed traffic.

This is why the existing 2.5GbE vs 10GbE Firewall Guide focuses on network topology rather than WAN speed alone. If a workstation and NAS sit on different VLANs, their transfer may traverse the firewall even when the internet is idle.

Routing and NAT: The Baseline Workload

Basic firewall routing, NAT and state tracking are the baseline. Modern x86 CPUs can handle substantial throughput when the rule set is simple and packets are large. But quoting one throughput number without packet size is misleading. Processing one gigabit of 64-byte packets requires far more packets per second than one gigabit of 1500-byte packets.

Netgate's pfSense hardware sizing guidance illustrates this explicitly: throughput changes significantly with frame size at the same packet rate. The same principle applies to any software firewall. If your environment carries many small packets, packets per second and interrupt/queue handling can matter as much as raw GHz.

NIC Quality Is Part of Firewall Performance

The NIC is not just a connector. Driver quality, queues, offloads and host interface bandwidth affect how much CPU time is spent moving packets. Netgate's sizing guidance notes that lower-quality adapters can consume more CPU, while better NICs can improve throughput with the same processor.

CWWK 2.5GbE platforms commonly use Intel i226 controllers. Intel lists the I226 family as supporting up to 2.5GbE per port over PCIe. For 10GbE, Intel's 500-series controller family includes 10GbE options used in server and network appliances. Choosing a well-supported NIC is especially important for OPNsense and pfSense because both depend on FreeBSD driver support.

VPN: Encryption Changes the CPU Requirement

A VPN turns the firewall into an encryption endpoint. Throughput now depends on the VPN protocol, cipher suite, packet size, number of tunnels and whether the CPU can accelerate the relevant cryptographic operations. WireGuard, IPsec and OpenVPN do not impose identical processing costs.

Do not take plain routing throughput and assume VPN will match it. If the use case requires multi-gigabit encrypted traffic, test the exact protocol and cipher. pfSense documentation notes that cryptographic acceleration can materially affect IPsec performance, while different VPN implementations carry different per-packet overheads.

IDS/IPS: Inspection Is a Different Class of Workload

Intrusion detection and prevention systems do more than forward packets. They inspect payloads, evaluate signatures and may keep flow state. This can consume substantial CPU and memory, especially with a large ruleset or multi-gigabit traffic.

The OPNsense hardware sizing guide explicitly identifies intrusion detection and prevention as a feature that changes hardware requirements. Netgate documentation similarly calls out Snort and Suricata as resource-intensive packages. That is why a firewall sized for basic NAT may be inadequate once IDS/IPS is enabled.

Memory: Usually Not the First Bottleneck, Until It Is

A basic firewall does not need workstation-class memory capacity, but memory becomes important with large state tables, IDS/IPS, caching services, logging, virtualized firewalls or additional packages. OPNsense documents roughly 1 kB per state entry as a sizing reference. Hundreds of thousands of concurrent connections therefore deserve deliberate memory planning.

For a home or small office firewall, 8GB often provides comfortable headroom for the base system and common features. Heavier IDS/IPS, virtualization or multiple services can justify 16GB or more. The exact amount should follow measured usage rather than a generic rule.

2.5GbE vs 10GbE: The NIC Is Only the Ceiling

A 2.5GbE interface caps a single link at 2.5Gbps. A 10GbE interface raises that ceiling, but the CPU still has to route, filter, encrypt or inspect the traffic. The CWWK firewall mini PC collection spans both multi-port 2.5GbE and 10GbE designs, so the right model should be selected around enabled services rather than the highest port number.

For a 10GbE firewall, PCIe topology matters as well. A dual-port 10GbE controller needs enough host bandwidth, and adding NVMe or another NIC can share lanes on compact platforms. The next guide, 10GbE Firewall Hardware Requirements, focuses specifically on those bottlenecks.

How to Benchmark a Firewall Correctly

· State the software version and configuration.

· Define packet size or use a documented IMIX profile.

· Test both directions if the network is asymmetric.

· Measure plain routing first, then enable VPN or IDS/IPS one feature at a time.

· Record CPU utilization and temperatures, not just throughput.

· Use a client/server pair that can exceed the target firewall speed.

· Test long enough to reveal thermal throttling and queue buildup.

A single iperf3 result with maximum-size packets is useful as a baseline, but it is not a complete security workload. Real traffic mixes packet sizes and protocols, and security features change the processing path. A good benchmark isolates one variable at a time so you can see where the throughput is lost.

Choosing CPU Headroom

For light routing, low-power CPUs can be efficient. As VPN, IDS/IPS, multi-gigabit routing and virtualization are added, a higher-performance CPU becomes easier to justify. Frequency matters for per-flow and latency-sensitive work, while more cores help multi-threaded inspection and concurrent services. The balance depends on the firewall software and package behavior.

Avoid sizing to 100% CPU under the expected normal load. A firewall needs headroom for traffic bursts, rule reloads, logging and background services. Sustained operation near the ceiling usually produces worse latency before the link is technically saturated.

Mini PC vs 1U Firewall Performance

A mini PC can deliver excellent firewall performance when its CPU and NICs match the workload. A 1U rackmount appliance does not automatically route faster, but it can offer more thermal headroom, additional NICs, PCIe expansion and easier rack integration. The 1U Rackmount Firewall vs Mini PC Firewall article compares the form factors rather than assuming one is always faster.

A Simple Sizing Method

Start with the simplest configuration that can meet the required throughput, then add the security features one by one. This produces a more reliable capacity plan than selecting hardware by Ethernet speed alone.

FAQ

Does a 10GbE firewall need a high-end CPU?

Not necessarily for basic routing, but 10GbE VPN, IDS/IPS or heavy inter-VLAN inspection can require substantially more CPU. Test the actual feature set.

Why is VPN throughput lower than routing throughput?

Encryption and protocol processing add CPU work to every packet. The exact difference depends on the VPN protocol, cipher and CPU acceleration.

Can IDS/IPS use multiple CPU cores?

Modern inspection engines can use multiple threads, but scaling is not perfectly linear and depends on configuration, rule set and traffic distribution.

Is 8GB RAM enough for OPNsense or pfSense?

For many home and small-office deployments, yes. Large state tables, IDS/IPS, extra packages or virtualization may justify more.

Are Intel NICs required?

No, but well-supported NICs with mature drivers are strongly preferred. Both OPNsense and pfSense rely on FreeBSD hardware support.

Related CWWK Resources

· CWWK Firewall Mini PC Guide

· CWWK Firewall Mini PC Collection

· 2.5GbE vs 10GbE Firewall

· 10GbE Firewall Hardware Requirements

External References

· OPNsense Hardware Sizing

· pfSense Hardware Sizing Guidance

· Intel Ethernet Controller I226