Most engineers think…
Most people picture DDoS defense as 'a beefier firewall' or 'just buy more bandwidth'. That mental model fails you in an interview and in production — a stateful firewall is exactly what a half-open SYN flood is built to exhaust.
Radware DefensePro is a dedicated, stateless appliance: it inspects packets without holding session state, so a flood can't fill a connection table. It runs several detection engines — Behavioral DoS, SYN flood, NG DNS, signature and HTTPS flood — that feed a fuzzy-logic engine. That engine scores a 'degree of attack' and auto-builds a real-time signature in seconds, dropping only attack packets while flash-crowd traffic flows. It sits upstream of your firewall to protect it, and is managed centrally from APSolute Vision.
① Why a dedicated stateless box — DefensePro vs the firewall
The single most important idea: DefensePro is stateless. It does not participate in session setup and holds no session state, so a flood cannot exhaust it the way it exhausts a firewall or load balancer. It inspects traffic packet-by-packet and absorbs very high packet rates that would collapse a stateful device.
That is why position matters. DefensePro sits inline at the edge, upstream of the firewall, so it cleans traffic before the stateful gear ever sees it. The classic failure is a low-rate half-open SYN flood quietly filling a firewall's connection table while bandwidth looks normal — DefensePro stops that at the door and protects everything behind it: firewalls, load balancers and servers.
DefensePro's protections are mostly described as…
② The detection engines — what each one catches
DefensePro is not one detector; it runs a suite of engines in parallel. Behavioral DoS (BDoS) continuously baselines normal L3/L4 traffic and catches zero-day network floods that have no pre-known signature. SYN Flood / Connection-Limit Protection defends half-open, request and full-connection attacks, challenging clients (SYN cookies, safe-reset) so only verified connections pass.
The rest of the suite
NG DNS Flood Protection is a behavioral engine for query floods, from basic floods to random-subdomain Water Torture (e.g. Mirai). Signature-based Protection matches Radware's known-vulnerability and threat-intel feed to block known exploits and scanning. HTTPS/SSL Flood Protection is notable for being keyless — it detects encrypted floods without decrypting traffic, with optional TLS offload for deeper L7 challenge.
Baselines normal L3/L4 traffic and auto-builds real-time signatures to stop zero-day network floods while sparing legitimate flash crowds.
Challenges clients with SYN cookies / safe-reset so verified connections pass and spoofed half-open floods are dropped — no session table to exhaust.
Behavioral engine for query floods including random-subdomain Water Torture; escalates challenge then rate-limit, then collective challenge/rate-limit.
Keyless detection of encrypted floods with no decryption needed; optional TLS offload (TLS 1.3, PFS) for deeper L7 challenge.
In an interview, separate the engines by what they catch: BDoS for zero-day network floods, SYN/Connection-Limit for half-open and connection attacks, NG DNS for query floods including Water Torture, Signature for known exploits, and keyless HTTPS for encrypted floods. 'It does DDoS' is not an answer — mapping engine to attack type is.
Which engine handles a zero-day network flood with no known signature?
③ Real-time signatures, step by step
This is the patented core. DefensePro continuously baselines normal traffic, then a fuzzy-logic inference engine combines rate-based parameters (pps, Mbps, connection rate, request rate) and rate-invariant parameters to compute a degree of attack. When that score is high, it isolates the anomalous pattern and emits a footprint — a precise real-time signature, typically built in about 10–18 seconds.
The footprint blocks only matching attack traffic, so legitimate flash-crowd spikes are spared. Mitigation then escalates rather than blunt-blocking. For DNS the ladder runs: signature challenge → signature rate-limit → collective challenge → collective rate-limit of all queries to the protected server — each rung more severe, the last a last resort.
DefensePro's headline capability is the opposite of a static signature feed: a fuzzy-logic engine scores a degree of attack and builds the signature on the fly in seconds. The signature feed exists too (for known exploits), but the behavioral footprint is what stops zero-day floods while letting flash crowds through.
▶ Watch a SYN flood get challenged and dropped at the edge
How DefensePro inspects and mitigates an attack end-to-end. Press Play for the healthy path, then Break it to see the classic failure.
Real-time signatures in DefensePro are built using…
④ Deploy and operate — inline, sizing, APSolute Vision, hybrid
To actively block, deploy DefensePro inline as a transparent L2 bridge; for detection-only, use copy/SPAN mode. Inline deployments use optical/copper bypass for fail-open so a hardware fault doesn't break the link. Size by throughput: the X10/X20 handle up to 20 Gbps mitigation for enterprise/MSSP, while the X400/X800 scale to 800 Gbps and ~1.1B pps for carriers and scrubbing centers; an XVA virtual appliance runs on VMware/KVM.
Manage and extend
Everything is driven from APSolute Vision — build Network Protection profiles, watch live attacks and mitigation actions on security dashboards, run forensics and reports, and push policy to many devices via the APSolute API. For attacks bigger than your pipe, pair on-prem with Radware Cloud DDoS for hybrid defense: the local box handles everyday floods and signals the cloud to scrub volumetric attacks.
Vikram Reddy at a Hyderabad ISP faces this
Customers of Deccan Broadband report intermittent web/app timeouts every evening, and the perimeter firewall's session table is maxing out at peak even though bandwidth looks normal.
A low-rate half-open SYN flood is exhausting the stateful firewall, which sits in front of (not behind) the DDoS appliance — so DefensePro never sees the attack first.
In APSolute Vision the SYN-flood and Connection-Limit counters are near zero while the firewall logs show TCP half-open growth, confirming DefensePro is mis-positioned downstream and SYN protection isn't engaging.
APSolute Vision ▸ Configuration ▸ Network Protection ▸ policy + Security Monitoring dashboardRe-cable so DefensePro is inline at the edge upstream of the firewall, enable SYN Flood Protection with SYN-cookie/safe-reset challenge in the policy, and deploy.
Replay/observe peak traffic — APSolute Vision shows SYN challenges issued and attack traffic dropped, the firewall's session count returns to baseline, and customer timeouts stop.
Never close a DDoS ticket on 'should be fine'. The APSolute Vision security dashboard shows the live attack, which engine engaged, the footprint, and the mitigation action taken. That single view tells you whether the box is positioned correctly and actually dropping the attack.
To actively block attacks rather than just detect them, DefensePro is deployed…
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📖 Glossary
- DefensePro
- Radware's on-prem, stateless DDoS mitigation appliance (Cisco OEMs it as Secure DDoS Protection).
- Behavioral DoS (BDoS)
- Engine that baselines L3/L4 traffic and auto-builds real-time signatures to stop zero-day floods while sparing flash crowds.
- Real-time signature / footprint
- An attack footprint generated on the fly to block only malicious packets — typically built in about 10–18 seconds.
- Stateless mitigation
- Packet-based defense that holds no session state, so floods can't exhaust it; it shields stateful firewalls and servers.
- Degree of attack
- A fuzzy-logic score of how abnormal traffic is versus baseline; a high score triggers footprint generation and mitigation.
- SYN flood
- Attack using half-open TCP handshakes to exhaust connection resources; mitigated with SYN cookies / safe-reset challenge.
- DNS Water Torture
- Random-subdomain query flood that overwhelms DNS resolvers/servers; caught by NG DNS Flood Protection.
- APSolute Vision
- Radware's central console to configure, monitor, report on and orchestrate DefensePro devices and hybrid cloud diversion.
- Hybrid DDoS
- On-prem DefensePro combined with on-demand Radware Cloud DDoS scrubbing for attacks larger than the local pipe.
📚 Sources
- Radware — Advanced DDoS Defense and Attack Mitigation | DefensePro. radware.com
- Radware Support — DefensePro – a Stateless Anti-DDoS Mitigation Device (KB). support.radware.com
- Radware WebHelp — DefensePro DoS/DNS Protection Mitigation Methods. webhelp.radware.com
- Radware / Cisco — DefensePro X / DPX & XVA models (Secure DDoS Protection). radware.com / cisco.com
- Radware Portals — DefensePro v10 Release Notes (X10/X20, X400/X800). portals.radware.com
- Radware Appliances — DefensePro x4420 Series Technical Specifications. radappliances.com
What's next?
Got the appliance? Next, go deep on hybrid DDoS — how on-prem DefensePro signals Radware's Cloud DDoS scrubbing centers to divert traffic over BGP/GRE when a volumetric attack exceeds your pipe, and how the two stay in sync.