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ASN

Look up an Autonomous System Number to see its name, allocated prefixes, upstream providers and peering relationships. Essential for network engineers diagnosing routing issues or analyzing traffic paths.

What it is

An ASN (Autonomous System Number) identifies an autonomous system in BGP. It helps analyze routes and providers.

How it works

Find an ASN by IP or number. Review announced prefixes, upstreams and geography.

Examples

  • ASN prefixes: the list of announced networks.
  • Upstream/Peers: transit providers and BGP neighbors.

Limitations & notes

Announcements change dynamically. Data refresh can lag.

FAQ

  • What is an ASN used for? An Autonomous System Number identifies a network or group of networks under a single administrative policy. Network engineers use ASN lookups to diagnose routing problems, trace traffic paths, verify IP ownership and understand peering relationships between ISPs.
  • Are there private ASNs? Yes, IANA reserves ASN ranges 64512-65534 (16-bit) and 4200000000-4294967294 (32-bit) for private use. These are used in internal BGP configurations and are not announced on the public Internet, similar to how private IP ranges like 10.0.0.0/8 work.
  • What is BGP? BGP (Border Gateway Protocol) is the routing protocol that holds the Internet together. Each AS uses BGP to announce its IP prefixes to neighboring networks, allowing routers worldwide to find the best path to any destination. BGP decisions are based on AS path length, policies and peering agreements.
  • How do I find which ASN owns an IP address? Enter the IP address into our IP lookup tool - it shows the ASN in the results. Alternatively, you can query a WHOIS database or use the command whois -h whois.radb.net <IP> to find the origin AS for any IP prefix.

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