IP2Location Block Visitors by ASN is a tool that generates firewall configuration rules to block network traffic based on Autonomous System Numbers (ASN). Users can specify ASN numbers and select IP address versions (IPv4 or IPv6) to generate blocking rules in various formats. The tool supports multiple output formats including Apache .htaccess (versions 2.0-2.4), Nginx, Linux iptables, CIDR, Netmask, Inverse Netmask, IIS web.config, Cisco ACL, PeerGuardian2, network-object, Cisco bit bucket, Juniper Junos, MikroTik, WatchGuard Firebox, and ConfigServer Firewall (CSF). Rules can be configured for both allow and deny actions depending on the platform and requirements. A free web-based interface allows manual downloads of firewall lists for individual ASN selections. The commercial Firewall IP List API enables automated daily downloads and supports multiple countries or ASN numbers in a single API call (maximum 10 ASN per request). The API returns compressed gzip files containing the firewall rules and can be accessed using scripting languages or command-line tools like cURL and wget. The API supports parameters for authentication tokens, ASN selection, output format, action type (allow/deny), IP version, and file type (gzip or plain text). This service is designed for network administrators and security teams who need to manage traffic filtering based on network ownership and origin.