What Is Cloudflare? How BotBlocker Detects Cloudflare by IP and Headers and When to Block

Cloudflare is one of the world’s largest providers of website protection, CDN (Content Delivery Network), and DDoS mitigation. Millions of websites use Cloudflare to speed up delivery, secure against attacks, and hide their real server IPs. But Cloudflare is also a popular entry point for bots, attackers, scrapers, and anonymizers – sometimes intentionally, sometimes not.

What Is Cloudflare?

Cloudflare acts as a reverse proxy between websites and their visitors. When you visit a site behind Cloudflare, your browser connects to Cloudflare’s servers, which then pass requests to the real web server. This setup brings benefits:

• Protection against DDoS and brute-force attacks
• Global caching for faster content delivery
• Hiding server infrastructure from the public

However, attackers, spammers, and bots also use Cloudflare’s network to mask their origin or bypass IP-based blocks.

How BotBlocker Detects Cloudflare

By IP Ranges

Cloudflare publishes a public list of IPv4 and IPv6 ranges that belong to its network. BotBlocker checks every visitor IP against these ranges in real time. If the request comes from a known Cloudflare address block, BotBlocker flags it immediately. These IP ranges are updated regularly and are available directly on the official Cloudflare IP list page, so detection stays accurate even as the network grows.

By HTTP Headers

Requests routed through Cloudflare often include specific HTTP headers, such as:

• CF-Connecting-IP
• CF-IPCountry
• CF-RAY
• CF-Visitor
• X-Forwarded-For (not exclusive to Cloudflare, but often present)

BotBlocker inspects these headers for signs of Cloudflare proxying. When a request carries one or more of these headers, it is a strong signal that the connection has passed through the Cloudflare network rather than coming directly from the end user. This matters because the visible IP in such cases belongs to Cloudflare’s infrastructure, not the actual visitor. Standard IP-based blocking will not reach the real source without this additional header analysis. You can read more about how HTTP request headers work in the MDN Web Docs reference on HTTP headers.

Why Is This Useful?

• Detecting masked bots: Attackers and scrapers often use Cloudflare to hide real source IPs and rotate addresses easily.
• Preventing abuse: Cloudflare’s free tier is sometimes used for launching automated attacks or evading restrictions.
• Better analytics: Knowing traffic comes from Cloudflare helps you correctly interpret visitor IPs and behavior.

When Should You Block or Restrict Cloudflare Traffic?

When to Consider Blocking or Challenging

• API endpoints, XML-RPC, admin panels, and sensitive forms: If only known users should access these areas, you might block or challenge all traffic routed through Cloudflare proxies.
• When you see high volumes of bot or abusive traffic coming via Cloudflare: Particularly common on public blogs, login forms, and comment systems.
• To enforce geo-blocking or restrict access to your site by region: Since Cloudflare can hide the real IP, you may want stricter rules for such traffic.

When Not to Block

• If your own site uses Cloudflare as a CDN or firewall, do not block Cloudflare IPs, or you will lock out all legitimate users.
• If you have legitimate users behind Cloudflare-protected networks: Some corporate, university, or shared networks route traffic via Cloudflare.

Best Practices

• Use BotBlocker’s detection as part of a layered approach – combine with User-Agent, Accept-Language, PTR, Referer and behavioral checks.
• Challenge suspicious Cloudflare traffic with captchas or multi-factor authentication, instead of outright blocking, for critical actions.
• Monitor your logs to adjust filtering as needed and avoid accidental lockouts.
• Keep your IP range data current. Since the network infrastructure can change, relying on an outdated list reduces detection accuracy. Automate the update process where possible.
• Use rate limiting alongside proxy detection. Even if a request comes from a recognized proxy network, high request frequency is a reliable signal of automated behavior. Combining both checks gives you better coverage with fewer false positives. For guidance on rate limiting strategies, see the OWASP recommendations on blocking brute-force attacks.

FAQ

Can blocking Cloudflare block real users?
Yes, if not used carefully – especially if your site or partners use Cloudflare. Review your traffic before enabling strict blocks.

Why not block all Cloudflare traffic by default?
Because many real sites and users rely on it. Blocking it entirely usually is not practical.

Does BotBlocker block Cloudflare traffic automatically?
No, it only detects and flags it. Blocking is up to your settings.

How often does BotBlocker update the IP ranges it checks?
BotBlocker syncs with the published IP range data on a regular basis to keep detection reliable. You can also manually trigger an update from the plugin settings if you want to make sure you have the latest data before making major changes to your blocking rules.

Is proxy detection enough on its own?
No. Proxy and CDN detection tells you where a request passed through, not who sent it or why. Use it as one signal in a broader set of checks that also covers request behavior, headers, and request frequency. That combination gives you a much more accurate picture of what is real traffic and what is not.