ASN Information Lookup

Introduction:

An Autonomous System Number (ASN) uniquely identifies a network or collection of IP prefixes that share a single, clearly-defined routing policy. It enables Border Gateway Protocol (BGP) routers to exchange reachability information, ensuring packets choose valid paths across the global Internet. Allocations are governed by regional internet registries, preserving address-space integrity.

Using a single input—either an ASN such as AS15169 or any IPv4/IPv6 address—the tool interrogates authoritative registries through a lightweight reactive engine. It resolves the address to its parent ASN, retrieves real-time registration data, announced prefixes, and live peer counts, then formats the findings in a structured summary and downloadable JSON.

Network operators compare providers, trace incident scope, or validate peering agreements before a maintenance window. Consultants use it during audits to verify ownership lines, while educators demonstrate BGP concepts in the classroom. Interpret results alongside routing tables; misconfigured announcements can propagate rapidly. Field engineers can also pre-check supplier ASNs to avoid fat-finger errors that might trigger route filtering.

Technical Details:

Autonomous System Numbers sit at the core of inter-domain routing. Every BGP UPDATE message carries an ordered list of ASNs—its AS-PATH—which lets routers detect loops and select optimal routes. Two ASN ranges exist: 0–65535 (16-bit) legacy and 131072–4294967295 (32-bit) expanded. Registries attach metadata such as holder name, country code, and operational status, assisting engineers in provenance checks and policy enforcement.

1. Normalize Input – Strip the AS prefix or validate dotted/colon IP text.
2. Translate IP → ASN – Query a geolocation service to obtain the owning ASN (a).
3. Registry Lookup – Call RIPE Stat datasets for a: overview, announced prefixes, peer counts, neighbours.
4. Aggregate Results – Merge responses, derive upstream and downstream totals, expose JSON.

• ASN / IP – Primary query value (string).
• Prefixes – Announced CIDR blocks (array).
• Peers – Adjacent ASNs classified as upstream or downstream.
• Status – Registry lifecycle flag.
• Timestamps – First-seen and last-updated dates (ISO 8601).

• Relies on public registry snapshots; updates may lag by several minutes.
• Private ASNs
are excluded because they are not globally routable.
• IPv6 translation depends on geolocation coverage.
• Peer counts aggregate RIS collectors, not every exchange point.

• Malformed input strings (AS----) trigger validation errors.
• Newly issued ASNs without prefixes return blank tables.
• Multi-origin prefixes may inflate peer totals.
• Proxy outages introduce transient “Lookup failed” messages.

Concepts align with RFC 1930 (Guidelines for AS Number Allocation) and RFC 4271 (BGP-4), both detailing ASN semantics and routing dynamics.

No personal data is processed; queries target public registry endpoints compliant with global data-sharing policies.

Step-by-Step Guide:

Follow these steps to obtain an immediate overview.

1. Enter the ASN or IP in the field provided.
2. Press Enter or select Lookup.
3. Review the summary banner for holder, country, and status.
4. Select Prefixes, Peers, or JSON to explore details.
5. Use Copy buttons or Download JSON to share results.

FAQ:

Glossary:

ASN

Unique numeric identifier for an autonomous network.

BGP

Protocol that exchanges reachability information between ASNs.

Prefix

CIDR block announced by an ASN.

Upstream

Provider ASN that carries outbound traffic.

Downstream

Customer ASN receiving transit or partial routes.