AS Lookup - Autonomous System Analysis for Network Operators

Query any Autonomous System to retrieve detailed routing information, announced prefixes, and network relationships. AS lookup provides the BGP intelligence network engineers need for peering decisions, troubleshooting, and infrastructure planning.

Autonomous System Fundamentals

The internet is a network of networks. Each network operating independently - making its own routing decisions - is an Autonomous System. The AS number identifies it globally.

Network operators need AS data for:

• Peering evaluation - Understanding a potential peer's network size and routing policy
• Troubleshooting - Identifying which AS is responsible for routing anomalies
• Capacity planning - Analyzing traffic sources by origin AS
• Security - Attributing malicious traffic to responsible networks

What AS Lookup Returns

• Organization - The entity operating the AS
• Announced prefixes - All IPv4 and IPv6 blocks advertised via BGP
• Upstream providers - Transit relationships visible in BGP paths
• Downstream customers - Networks receiving transit from this AS
• IXP presence - Internet exchange points where the AS peers
• Routing policy - Import/export rules from IRR databases

Network Operator Use Cases

Transit selection - Compare potential upstream providers by their prefix counts, geographic reach, and peering relationships. More peers generally means better connectivity.

Prefix hijack detection - Monitor whether your prefixes appear in BGP from unauthorized ASNs. AS lookup helps identify legitimate vs. suspicious announcements.

Path analysis - Understand why traffic takes specific routes by examining AS relationships along the path.

Peering requests - Build a case for peering by demonstrating traffic volume and network characteristics.

Reading BGP Data

AS path length affects routing decisions. Shorter paths are preferred. AS lookup shows typical path lengths to major destinations, helping evaluate connectivity quality.

Prefix granularity matters. Networks announcing many /24s have different characteristics than those with aggregated larger blocks. This affects route table size and routing stability.

→ Query an AS

FAQ

How do I find my organization's ASN? Check your IP allocation from your regional internet registry, or query any IP address you control to see its announcing AS.

What's the difference between transit and peering? Transit is paid connectivity where one AS carries another's traffic to the full internet. Peering is mutual exchange of customer traffic, typically settlement-free.

Why do some ASNs show no prefixes? The AS may exist but not currently announce routes (dormant), or may be used only for internal purposes without public routing.

How current is BGP data? BGP routing tables update continuously. AS lookup reflects recent routing state, though propagation delays mean changes take minutes to appear globally.