We offer a free database that maps IPv4 addresses to ASN, including the name of the ASN. The GeoIPASNum.dat.gz file works with our APIs, by calling the same methods as used by the organization database. The GeoIPASNum2.zip file contains a CSV formatted database. The database is updated every month.

Under the license agreement, all advertising materials and documentation mentioning features or use of this database must display the following acknowledgment: "This product includes GeoLite data created by MaxMind, available from http://www.maxmind.com/."

Please visit the MaxMind Forum if you encounter problems or have any questions.

Team Cymru has an IP to ASN Lookup Page.