What is an ASN?
An Autonomous System Number identifies a network (an ISP, a cloud provider, a large enterprise) that has its own routing policy on the public internet. ASNs are how BGP — the protocol that holds the internet together — knows which network owns which range of IP addresses. AS55390 is the ASN assigned to TUSNET Tokyo University of Science.
If you want to know which ASN your connection is on, visit the home page — your ASN is shown alongside your public IP.
Data source
This page is generated server-side from RIPE Stat (free, public, no API key). Holder names, country codes, and announced prefixes come directly from RIPE's BGP table view. Cached for one hour at the edge.