Enter an ASN to view its BGP history, prefixes, peers, and network topology
An Autonomous System Number (ASN) is a unique identifier assigned to each autonomous system (AS) on the Internet. An autonomous system is a collection of connected IP routing prefixes under the control of one or more network operators that presents a common, clearly defined routing policy to the Internet.
ASNs are a critical component of the Border Gateway Protocol (BGP), which is the routing protocol that makes the Internet work. Every ISP, cloud provider, large enterprise, and university network operates as an autonomous system with its own ASN.
BGP (Border Gateway Protocol) is the postal system of the Internet. It determines how data packets travel between autonomous systems. When you visit a website, BGP routes your request through multiple ASNs to reach the destination server.
The BGP topology of an ASN reveals its relationships with other networks. Upstream providers are larger networks that provide transit connectivity to the broader Internet, while downstream networks are smaller networks that purchase connectivity from the ASN in question.
Network Troubleshooting: Understanding an ASN's prefixes and peers helps diagnose connectivity issues, routing loops, and BGP hijacking attempts.
Security Research: Security analysts use ASN data to trace malicious infrastructure, identify hosting providers used by threat actors, and map attack paths.
Business Intelligence: Companies analyze ASN data to understand their network dependencies, evaluate peering relationships, and plan infrastructure improvements.
Compliance & Auditing: ASN history helps verify that network resources are allocated correctly and identify unauthorized changes to routing policies.
You can enter ASNs in either format: with the "AS" prefix (e.g., AS13335) or as a plain number (e.g., 13335). Both formats will be normalized automatically.
An upstream provider is a larger network that provides Internet transit to a smaller network. For example, a regional ISP may purchase transit from a Tier 1 provider like AT&T or NTT, making those upstreams of the ISP.
BGP routing data changes dynamically in real-time as networks adjust their routing policies. Our tool queries the BGPView API which maintains a near-real-time view of global BGP routing tables.
BGP hijacking occurs when a malicious actor announces IP prefixes that they do not own, causing traffic intended for the legitimate owner to be routed through the attacker's network. ASN monitoring tools like this one help detect such incidents.