Implementing DDoS Mitigation with Cloudflare

Overview

Cloudflare provides multi-layer DDoS protection across its global network of over 300 data centers with 477+ Tbps of capacity. The platform protects against L3/4 volumetric attacks (SYN floods, UDP amplification, DNS reflection), protocol attacks (Ping of Death, Smurf), and L7 application-layer attacks (HTTP floods, Slowloris, cache-busting). Cloudflare's autonomous detection systems identify and mitigate attacks within approximately 3 seconds using traffic profiling, machine learning, and adaptive rulesets. This skill covers configuring Cloudflare's DDoS protection stack including managed rulesets, WAF rules, rate limiting, Bot Management, and origin server hardening.

When to Use

• When deploying or configuring implementing ddos mitigation with cloudflare capabilities in your environment
• When establishing security controls aligned to compliance requirements
• When building or improving security architecture for this domain
• When conducting security assessments that require this implementation

Prerequisites

• Cloudflare account (Pro plan minimum for WAF, Enterprise for Advanced DDoS)
• Domain with DNS delegated to Cloudflare nameservers
• Origin server IP address(es)
• Understanding of normal traffic patterns and peak volumes
• Cloudflare API token for automation

Core Concepts

DDoS Attack Categories

Layer	Attack Type	Examples	Cloudflare Protection
L3/4	Volumetric	SYN flood, UDP flood, DNS amplification	Network-layer DDoS managed rules
L3/4	Protocol	Ping of Death, Smurf, IP fragmentation	Advanced TCP Protection
L7	Application	HTTP flood, Slowloris, cache busting	HTTP DDoS managed rules, WAF, Rate Limiting
DNS	DNS-specific	DNS query flood, NXDOMAIN attack	Advanced DNS Protection

Cloudflare Protection Stack

Internet Traffic
     │
     ▼
┌─────────────────────────┐
│  Cloudflare Edge (PoP)  │
│  ┌───────────────────┐  │
│  │ L3/4 DDoS Mgd Rules│  │  ← Volumetric/Protocol mitigation
│  └───────────────────┘  │
│  ┌───────────────────┐  │
│  │ IP Access Rules    │  │  ← Country/ASN/IP blocks
│  └───────────────────┘  │
│  ┌───────────────────┐  │
│  │ Bot Management     │  │  ← Bot score, JS challenge
│  └───────────────────┘  │
│  ┌───────────────────┐  │
│  │ WAF Managed Rules  │  │  ← OWASP, Cloudflare, Custom
│  └───────────────────┘  │
│  ┌───────────────────┐  │
│  │ Rate Limiting      │  │  ← Request rate enforcement
│  └───────────────────┘  │
│  ┌───────────────────┐  │
│  │ HTTP DDoS Mgd Rules│  │  ← L7 flood detection
│  └───────────────────┘  │
└─────────────────────────┘
     │
     ▼
  Origin Server

Workflow

Step 1: Onboard Domain to Cloudflare

# Add domain via API
curl -X POST "https://api.cloudflare.com/client/v4/zones" \
  -H "Authorization: Bearer $CF_API_TOKEN" \
  -H "Content-Type: application/json" \
  --data '{
    "name": "example.com",
    "type": "full",
    "plan": {"id": "enterprise"}
  }'

# Update DNS records (proxy enabled for DDoS protection)
curl -X POST "https://api.cloudflare.com/client/v4/zones/$ZONE_ID/dns_records" \
  -H "Authorization: Bearer $CF_API_TOKEN" \
  -H "Content-Type: application/json" \
  --data '{
    "type": "A",
    "name": "example.com",
    "content": "203.0.113.50",
    "proxied": true,
    "ttl": 1
  }'

Step 2: Configure DDoS Managed Rulesets

HTTP DDoS Attack Protection override:

# List HTTP DDoS managed ruleset
curl -X GET "https://api.cloudflare.com/client/v4/zones/$ZONE_ID/rulesets/phases/ddos_l7/entrypoint" \
  -H "Authorization: Bearer $CF_API_TOKEN"

# Override HTTP DDoS sensitivity and action
curl -X PUT "https://api.cloudflare.com/client/v4/zones/$ZONE_ID/rulesets/phases/ddos_l7/entrypoint" \
  -H "Authorization: Bearer $CF_API_TOKEN" \
  -H "Content-Type: application/json" \
  --data '{
    "rules": [{
      "action": "execute",
      "action_parameters": {
        "id": "4d21379b4f9f4bb088e0729962c8b3cf",
        "overrides": {
          "rules": [{
            "id": "fdfdac75430c4c47a422bdc024aab531",
            "sensitivity_level": "medium",
            "action": "block"
          }],
          "sensitivity_level": "high"
        }
      },
      "expression": "true"
    }]
  }'

Network-layer DDoS Protection override:

curl -X PUT "https://api.cloudflare.com/client/v4/accounts/$ACCOUNT_ID/rulesets/phases/ddos_l4/entrypoint" \
  -H "Authorization: Bearer $CF_API_TOKEN" \
  -H "Content-Type: application/json" \
  --data '{
    "rules": [{
      "action": "execute",
      "action_parameters": {
        "id": "3b64149bfa6e4220bbbc2bd6db7c867e",
        "overrides": {
          "sensitivity_level": "high"
        }
      },
      "expression": "true"
    }]
  }'

Step 3: Configure Rate Limiting Rules

# Create rate limiting rule for login endpoint
curl -X POST "https://api.cloudflare.com/client/v4/zones/$ZONE_ID/rulesets/phases/http_ratelimit/entrypoint" \
  -H "Authorization: Bearer $CF_API_TOKEN" \
  -H "Content-Type: application/json" \
  --data '{
    "rules": [
      {
        "description": "Rate limit login attempts",
        "expression": "(http.request.uri.path eq \"/api/login\")",
        "action": "block",
        "ratelimit": {
          "characteristics": ["cf.colo.id", "ip.src"],
          "period": 60,
          "requests_per_period": 10,
          "mitigation_timeout": 600
        }
      },
      {
        "description": "Rate limit API endpoints",
        "expression": "(http.request.uri.path matches \"^/api/\")",
        "action": "managed_challenge",
        "ratelimit": {
          "characteristics": ["cf.colo.id", "ip.src"],
          "period": 60,
          "requests_per_period": 100,
          "mitigation_timeout": 300
        }
      },
      {
        "description": "Global rate limit per IP",
        "expression": "true",
        "action": "managed_challenge",
        "ratelimit": {
          "characteristics": ["ip.src"],
          "period": 10,
          "requests_per_period": 50,
          "mitigation_timeout": 60
        }
      }
    ]
  }'

Step 4: Configure WAF Custom Rules

# Block known attack patterns
curl -X POST "https://api.cloudflare.com/client/v4/zones/$ZONE_ID/rulesets/phases/http_request_firewall_custom/entrypoint" \
  -H "Authorization: Bearer $CF_API_TOKEN" \
  -H "Content-Type: application/json" \
  --data '{
    "rules": [
      {
        "description": "Block requests from known bad ASNs",
        "expression": "(ip.geoip.asnum in {12345 67890})",
        "action": "block"
      },
      {
        "description": "Challenge requests without User-Agent",
        "expression": "(not http.user_agent ne \"\")",
        "action": "managed_challenge"
      },
      {
        "description": "Block high-risk countries for admin paths",
        "expression": "(http.request.uri.path contains \"/admin\" and not ip.geoip.country in {\"US\" \"CA\" \"GB\"})",
        "action": "block"
      },
      {
        "description": "Block oversized request bodies",
        "expression": "(http.request.body.size gt 10000000)",
        "action": "block"
      }
    ]
  }'

Step 5: Configure Origin Protection

Ensure the origin server only accepts traffic from Cloudflare:

# Get Cloudflare IP ranges
curl https://api.cloudflare.com/client/v4/ips

# Configure origin server firewall (iptables)
# Allow only Cloudflare IPs
for ip in $(curl -s https://www.cloudflare.com/ips-v4); do
    iptables -A INPUT -p tcp --dport 443 -s $ip -j ACCEPT
    iptables -A INPUT -p tcp --dport 80 -s $ip -j ACCEPT
done

# Drop all other HTTP/HTTPS traffic
iptables -A INPUT -p tcp --dport 443 -j DROP
iptables -A INPUT -p tcp --dport 80 -j DROP

# Enable Authenticated Origin Pulls (mutual TLS)
# Download Cloudflare origin CA certificate
curl -o /etc/ssl/cloudflare-origin-pull.pem \
  https://developers.cloudflare.com/ssl/static/authenticated_origin_pull_ca.pem

# Nginx configuration for authenticated origin pulls
# ssl_client_certificate /etc/ssl/cloudflare-origin-pull.pem;
# ssl_verify_client on;

Step 6: Enable Under Attack Mode Automation

#!/usr/bin/env python3
"""Auto-enable Cloudflare Under Attack Mode based on traffic anomalies."""

import requests
import time
import sys

CF_API_TOKEN = "your-api-token"
ZONE_ID = "your-zone-id"
HEADERS = {
    "Authorization": f"Bearer {CF_API_TOKEN}",
    "Content-Type": "application/json",
}
BASE_URL = f"https://api.cloudflare.com/client/v4/zones/{ZONE_ID}"

NORMAL_RPS_THRESHOLD = 5000  # Requests per second threshold
CHECK_INTERVAL = 30  # Seconds between checks


def get_current_security_level():
    """Get current security level setting."""
    resp = requests.get(
        f"{BASE_URL}/settings/security_level",
        headers=HEADERS
    )
    return resp.json()["result"]["value"]


def set_security_level(level: str):
    """Set security level (off, essentially_off, low, medium, high, under_attack)."""
    resp = requests.patch(
        f"{BASE_URL}/settings/security_level",
        headers=HEADERS,
        json={"value": level}
    )
    result = resp.json()
    if result["success"]:
        print(f"[+] Security level set to: {level}")
    else:
        print(f"[-] Failed to set security level: {result['errors']}")
    return result["success"]


def get_traffic_analytics():
    """Get recent traffic data from Cloudflare analytics."""
    query = """
    query {
      viewer {
        zones(filter: {zoneTag: "%s"}) {
          httpRequests1mGroups(limit: 1, orderBy: [datetime_DESC]) {
            sum {
              requests
              threats
            }
            dimensions {
              datetime
            }
          }
        }
      }
    }
    """ % ZONE_ID

    resp = requests.post(
        "https://api.cloudflare.com/client/v4/graphql",
        headers=HEADERS,
        json={"query": query}
    )
    return resp.json()


def monitor_and_respond():
    """Monitor traffic and auto-enable under attack mode."""
    current_level = get_current_security_level()
    print(f"[*] Current security level: {current_level}")
    print(f"[*] Monitoring traffic (threshold: {NORMAL_RPS_THRESHOLD} RPS)...")

    attack_mode_active = False
    consecutive_normal = 0

    while True:
        try:
            analytics = get_traffic_analytics()
            zones = analytics.get("data", {}).get("viewer", {}).get("zones", [])

            if zones and zones[0].get("httpRequests1mGroups"):
                data = zones[0]["httpRequests1mGroups"][0]["sum"]
                rps = data["requests"] / 60
                threats = data["threats"]

                print(f"[*] Current RPS: {rps:.0f}, Threats: {threats}")

                if rps > NORMAL_RPS_THRESHOLD and not attack_mode_active:
                    print(f"[!] Traffic spike detected: {rps:.0f} RPS")
                    set_security_level("under_attack")
                    attack_mode_active = True
                    consecutive_normal = 0

                elif rps <= NORMAL_RPS_THRESHOLD and attack_mode_active:
                    consecutive_normal += 1
                    if consecutive_normal >= 5:
                        print("[+] Traffic normalized, disabling under attack mode")
                        set_security_level("high")
                        attack_mode_active = False
                        consecutive_normal = 0

        except Exception as e:
            print(f"[-] Error: {e}")

        time.sleep(CHECK_INTERVAL)


if __name__ == "__main__":
    monitor_and_respond()

Monitoring and Alerting

Cloudflare Dashboard Metrics

• Firewall Events - View blocked requests, challenged requests, rate-limited requests
• DDoS Analytics - Attack size, duration, type, and mitigation status
• Traffic Analytics - Request volume, bandwidth, error rates by time
• Bot Analytics - Bot score distribution, verified bots vs automated threats

Alert Configuration

# Create notification policy for DDoS attacks
curl -X POST "https://api.cloudflare.com/client/v4/accounts/$ACCOUNT_ID/alerting/v3/policies" \
  -H "Authorization: Bearer $CF_API_TOKEN" \
  -H "Content-Type: application/json" \
  --data '{
    "name": "DDoS Attack Alert",
    "alert_type": "dos_attack_l7",
    "enabled": true,
    "mechanisms": {
      "email": [{"id": "soc@example.com"}],
      "webhooks": [{"id": "webhook-id"}]
    },
    "filters": {
      "zones": ["'$ZONE_ID'"]
    }
  }'

Best Practices

• Proxy All DNS Records - Ensure all A/AAAA/CNAME records pointing to origin are proxied (orange cloud)
• Hide Origin IP - Never expose origin server IP; use Cloudflare Tunnel or restrict to Cloudflare IPs only
• Start in Log Mode - Test DDoS rule overrides with "Log" action before switching to "Block"
• Layer Defense - Combine managed rulesets, rate limiting, WAF rules, and Bot Management
• Tune Sensitivity - Adjust DDoS rule sensitivity based on false positive rates in your traffic
• Cache Strategy - Maximize cache hit ratio to reduce origin load during attacks
• Waiting Room - Configure Cloudflare Waiting Room for critical pages during traffic surges
• Authenticated Origin - Enable Authenticated Origin Pulls to prevent direct-to-origin attacks

References

• Cloudflare DDoS Protection Documentation
• Cloudflare WAF Documentation
• Cloudflare Rate Limiting
• Cloudflare IP Ranges