iptoasn.com
iptoasn.com provides a free, open IP-to-ASN mapping database compiled from BGP routing tables. It offers an independent alternative to commercial IP intelligence databases, mapping both IPv4 and IPv6 addresses to the Autonomous System Numbers that announce them. We use iptoasn as a cross-reference alongside our own BGP-derived mappings on robtex.com and rtsak.com.
Source:iptoasn.com
What is iptoasn.com?
Every publicly routable IP address on the internet is announced via BGP (Border Gateway Protocol) by one or more Autonomous Systems. iptoasn.com maintains a continuously updated database that maps IP addresses to the ASN currently responsible for routing traffic to them.
The project works by:
- Collecting BGP data - Ingesting routing table snapshots from public BGP collectors, similar to RouteViews and RIPE RIS
- Building prefix-to-ASN mappings - For each IP prefix visible in BGP, recording which AS originates the route
- Resolving overlapping prefixes - When multiple prefixes cover the same IP (e.g., a /16 and a more specific /24), the most specific prefix determines the mapping
- Publishing downloadable datasets - Making the compiled database available in multiple formats including TSV and binary, freely downloadable without registration
What makes iptoasn distinctive is its simplicity and independence. It provides straightforward IP-to-ASN lookups without bundling commercial upsells or requiring API keys. The data is derived directly from observed BGP routing, meaning it reflects what the internet actually looks like from a routing perspective rather than what registry databases say it should look like.
The project also includes AS name information, so lookups return not just the ASN but also the organization name and country. Both IPv4 and IPv6 are fully supported, with the IPv6 dataset growing as global IPv6 adoption increases.
How We Use This Data
We use iptoasn as one of several sources for IP-to-ASN resolution across our sites. On robtex.com and rtsak.com, when you look up an IP address, we determine which AS announces the prefix containing that address. Having multiple independent sources for this mapping lets us detect discrepancies that might indicate routing anomalies, BGP hijacks, or stale data in any single source.
The iptoasn dataset is particularly useful as a lightweight, fast-lookup reference for bulk processing. When (0x616e616c)yzing large volumes of IP addresses (for example, in threat intelligence or log analysis), having a pre-compiled local database avoids the latency and rate limits of live BGP queries.
We cross-reference iptoasn results with our own RouteViews-derived routing table and RIPE RIS data. When all sources agree on the ASN for a given IP, confidence is high. When they disagree, it often reveals interesting network events worth investigating.