The State of Open-Source DDoS Detection
Open-source DDoS detection tools have come a long way. What once required expensive commercial platforms can now be partially replicated with free tools that run on commodity hardware. For small deployments, individual hobbyists, or engineers doing quick diagnostics, open-source tools are the right starting point.
But there is a gap between what open-source tools can do and what production DDoS detection requires. That gap has widened as attackers have gotten more sophisticated: multi-vector attacks, shorter burst durations, application-layer floods, and botnets that ramp carefully to stay below threshold limits. Understanding exactly where open-source tools hit their ceiling, and what that means operationally, is the goal of this guide.
This is not a piece designed to push you toward paid tools. The open-source options covered here are genuinely useful. But honesty matters: if you are protecting production infrastructure, knowing the limitations of free tools before an incident is better than discovering them during one.
The Tools
ftagent-lite
ftagent-lite is the open-source sibling of Flowtriq's commercial detection agent. It runs on any Linux server, requires no account or API key, and outputs real-time traffic statistics directly to stdout. It can detect traffic anomalies by PPS threshold, break down traffic by protocol (TCP, UDP, ICMP), track source IP counts, and output structured JSON for piping into your own tooling.
Install it with pip install scapy psutil and run with sudo python3 ftagent_lite.py. Add --json to pipe to jq, --watch for a live terminal dashboard, and --threshold 50000 to set your PPS alert threshold. It classifies severity as MEDIUM, HIGH, or CRITICAL based on multiples of the threshold.
ftagent-lite is excellent for: quick DDoS diagnostics on a single server, CI pipeline traffic validation, building custom alerting pipelines by piping JSON output to your own scripts, or as a learning tool to understand what attack traffic looks like at the packet level.
Limitations: stdout only (no cloud dashboard, no persistent incident history), no automated mitigation or alert delivery (Discord, Slack, PagerDuty), no PCAP capture, single-server only (no multi-node management), no attack classification beyond severity threshold levels, no dynamic baseline (fixed threshold).
FastNetMon Community
FastNetMon Community is the open-source edition of FastNetMon, a well-established DDoS detection tool popular in hosting and ISP environments. It collects NetFlow, sFlow, or IPFIX from your network equipment and applies threshold-based detection to identify volumetric anomalies. When a threshold is exceeded, it can trigger a BGP blackhole via ExaBGP, run a custom script, or send a syslog alert.
For organizations with existing flow-exporting routers or switches, FastNetMon Community is a strong free starting point. It is particularly effective at catching large volumetric floods at the network edge and triggering automated BGP responses. Deployment requires a Linux server that receives flow data plus a BGP-capable router for automated blackhole responses.
Limitations: No web UI or dashboard (CLI/config file only), limited alert channels (syslog, email via system mailer, script execution), no attack classification beyond protocol-level observation, detection latency tied to flow export intervals (commonly 30-60 seconds), flow sampling means short-duration or lower-volume attacks may be missed, no PCAP capture, requires flow-exporting network infrastructure. Community edition is maintained but feature development is prioritized in the commercial Advanced edition.
ntopng Community Edition
ntopng is a network traffic monitoring tool that provides a web-based dashboard for real-time and historical network analysis. The community edition supports flow-based monitoring (NetFlow, sFlow), packet capture from network interfaces, protocol breakdown, top talkers, and geographic visualization. It is primarily a visibility and monitoring tool, not a purpose-built DDoS detector.
ntopng can surface DDoS patterns visually: a sudden spike in top talkers, an unusual distribution of UDP traffic, or a geographic anomaly is immediately visible in the dashboard. For smaller networks where manual operator review is feasible, ntopng provides good situational awareness.
Limitations: No automated DDoS detection with configurable thresholds in the community edition (threshold alerting requires the enterprise version), no automated mitigation or BGP integration, designed for visibility rather than detection, no attack classification, requires manual investigation to identify and respond to attacks. The community edition has limited retention and lacks the alert system that makes ntopng operationally useful for DDoS response.
Suricata
Suricata is an open-source IDS/IPS engine that inspects network traffic using a rule-based signature system. It can detect DDoS-related patterns when appropriate rules are loaded, and it operates in inline mode (IPS) to block traffic matching rules. Suricata is extremely capable as a general-purpose network security monitor and is widely used for threat hunting and intrusion detection.
For DDoS detection specifically, Suricata works best when you have specific signatures to match against: known botnet C2 patterns, specific amplification reflection sources, or application-layer attack signatures. The Emerging Threats ruleset includes DDoS-related rules that can be loaded directly.
Limitations: Rule-based detection does not catch volumetric floods that do not match known signatures. Suricata has no built-in concept of traffic baselines, dynamic thresholds, or statistical anomaly detection. A 500,000 PPS UDP flood from clean source IPs will not trigger Suricata unless a matching rule exists. Managing rules at scale requires operational expertise. No cloud dashboard, no modern alert channels, no PCAP-to-incident linking. Suricata is a complement to DDoS detection, not a replacement.
pfSense + pfBlockerNG
pfSense is a widely deployed open-source firewall distribution. Combined with pfBlockerNG (IP reputation blocking), it can provide a basic layer of DDoS mitigation for smaller networks. Rate limiting rules, connection tracking, and geo-blocking can be configured to reduce attack surface.
Limitations: pfSense is a firewall, not a DDoS detection tool. It applies static rules rather than dynamically adapting to attack traffic. At high attack volumes (100,000+ PPS), pfSense's software-based packet processing becomes a bottleneck. There is no attack detection, no alerting system, no PCAP, and no attack classification. This is a reactive mitigation layer, not a detection platform.
Feature Comparison
| Capability | ftagent-lite | FastNetMon CE | ntopng CE | Suricata | Flowtriq |
|---|---|---|---|---|---|
| Cost | Free | Free | Free | Free | $9.99/node/mo |
| Detection method | Per-packet | Flow sampling | Flow / packet | Signature rules | Per-packet |
| Detection latency | 1-2 sec (manual) | 30-60 sec | Manual review | Rule-dependent | 1 second |
| Dynamic baselines | No | No | No | No | Yes |
| Attack classification | No | No | No | Signature only | 8 families + score |
| PCAP capture | No | No | Manual only | Log files only | Automatic |
| Automated mitigation | No | BGP blackhole | No | IPS drop (rules) | 22 action types |
| Modern alerts | stdout only | Syslog/email | Limited | Log files | Discord/Slack/PD/etc. |
| Cloud dashboard | No | No | Self-hosted web UI | No | Yes |
| Multi-node management | No | Single collector | Cluster (limited) | No | Yes |
| Deployment complexity | Low (pip install) | Medium (BGP infra) | Medium (server) | High (rules mgmt) | Low (2 min) |
The Production Gap
The table above reveals a consistent pattern: open-source tools cover detection basics but stop short of the capabilities that make DDoS response operationally effective in production. The three gaps that matter most in practice are:
1. Alert delivery
During an active DDoS attack, your on-call engineer needs to know about it within seconds, not whenever they next check a log file or terminal. None of the open-source tools listed above have native Discord, Slack, PagerDuty, OpsGenie, or SMS delivery. Building this with scripts is possible, but it adds fragile infrastructure that can fail exactly when you need it most. Ftagent-lite, for example, outputs to stdout: you would need to pipe that to a script that calls a webhook. That script is not monitored, tested, or maintained by anyone.
2. Attack classification
Knowing that traffic spiked is not the same as knowing it is a DNS amplification attack. The classification determines your mitigation response. A SYN flood and a UDP amplification attack require different firewall rules. Open-source tools either do not classify at all (FastNetMon CE, ntopng, ftagent-lite) or classify only what matches a known signature (Suricata). Automated classification with a confidence score is a commercial-tier capability.
3. PCAP forensics
After an attack, you need evidence: for upstream abuse reports, for post-mortem analysis, for proving to management what happened. Manually running tcpdump alongside any of these tools means either permanently capturing all traffic (expensive storage) or hoping you start the capture before the attack ends. Automatic PCAP capture with a pre-attack rolling buffer is not present in any of the open-source tools listed here.
Open-source tools are the right starting point for visibility and learning. They are not the right answer when downtime costs money, when SLAs exist, or when attacks are sophisticated enough to require classification-driven response. The upgrade path from open source to commercial is straightforward: ftagent-lite is a zero-install trial of what Flowtriq detects, without the response capabilities.
The Upgrade Path: ftagent-lite to Flowtriq
ftagent-lite was built specifically as the open-source version of Flowtriq's detection agent. This makes the upgrade path unusually clean. If you are running ftagent-lite and want to graduate to full production capabilities:
- Sign up for Flowtriq. No credit card required for the 7-day free trial. Your account is provisioned instantly.
- Install ftagent (the full agent) on the same server. The installation is a single command:
pip install ftagent, thensudo ftagent --setupwith your API key. - Configure your alert channels. Connect Discord, Slack, PagerDuty, OpsGenie, or email from the dashboard. This takes about two minutes.
- Set up mitigation rules (optional). Configure which attack types trigger automated responses. The dashboard provides pre-built rule templates for common attack types.
- Let baselines form. The agent learns your normal traffic patterns over 24-72 hours. After this, detection accuracy is at its best and false positives drop significantly.
The same agent code that ftagent-lite uses for traffic analysis runs in Flowtriq. You are not changing detection methodology; you are adding the cloud dashboard, alert delivery, attack classification, PCAP capture, and mitigation engine that turn raw detection into operational incident response.
Frequently Asked Questions
Is ftagent-lite maintained?
Yes. ftagent-lite is maintained by Flowtriq and available on GitHub under the MIT license. Version updates track the detection logic improvements made to the core Flowtriq agent. The repository accepts contributions and issue reports through the standard GitHub flow.
Can I run FastNetMon Community and Flowtriq together?
Yes, and for hosting providers and ISPs this combination is common. FastNetMon Community provides flow-based edge detection and BGP blackhole automation at the network layer. Flowtriq provides per-server detection depth, attack classification, PCAP, and targeted mitigation at the host layer. They operate independently and complement each other: FastNetMon catches large volumetric floods before they saturate transit; Flowtriq catches everything at the server level with full forensic detail.
Which open-source tool is best for a single server?
ftagent-lite is the most practical choice for single-server quick diagnostics. It requires nothing beyond Python and scapy, runs without root networking infrastructure, outputs clean JSON, and is designed specifically for host-level DDoS pattern detection. For a single server in production that needs real alerting and forensics, the upgrade path to Flowtriq is one command away.
What is the minimum cost for production-grade DDoS detection?
With Flowtriq, production-grade detection with classification, PCAP, and modern alerting starts at $9.99 per node per month. There is no minimum node count. A single server is $9.99/month, and the 7-day free trial requires no credit card. Compared to the engineering cost of self-hosting and maintaining open-source tooling at production quality, most teams find this significantly cheaper than building equivalent capabilities from scratch.
Does Suricata work for DDoS detection?
Suricata can detect some DDoS attack patterns using signature rules, but it is not designed as a DDoS detection platform. It has no threshold-based volumetric detection, no dynamic baselines, and no built-in concept of "packets per second exceeded normal." Suricata is excellent for detecting specific known attack patterns and malware behavior. For volumetric DDoS detection, it is a complement to dedicated tools rather than a replacement.
Start with ftagent-lite. Upgrade when you're ready.
ftagent-lite is free and open source on GitHub. When you need automatic PCAP, attack classification, and Discord/Slack/PagerDuty alerts, Flowtriq is the same agent with the production layer added. 7-day free trial, no credit card.