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Cloudflare's access restriction feature allows website owners to block traffic from specific autonomous system numbers (ASNs). This is useful for preventing abuse from known malicious networks or reducing load from unwanted regions.

• ASN-based blocking: Restrict access by ASN to block entire networks from reaching your site. Ideal for stopping repeated attacks from a specific ISP or hosting provider.
• Instant deployment: Rules apply immediately across Cloudflare's global network. No downtime or waiting for propagation.
• Customizable error pages: Choose a default Cloudflare error message or display your own branded page explaining the block.
• Integration with other rules: Combine ASN blocks with IP, country, or user-agent filters for layered security.
• Ray ID tracking: Each blocked request gets a unique Ray ID for debugging and logging. Use this ID to analyze traffic patterns or identify false positives.

This feature is part of Cloudflare's Web Application Firewall (WAF) and is available on most plans. It requires minimal configuration: enter the ASN number and choose the action (block, challenge, or log). For site owners needing granular control over incoming traffic, ASN blocking provides a practical, low-maintenance solution.