🌐 ASN Lookup

Search any Autonomous System Number or organization name — get BGP prefixes, peer count, RIR data, country, and full routing information.

Quick examples:
✍️ Author: ToolsNovaHub Editorial Team • ✅ Reviewed by: ToolsNovaHub Network Team • 📅 Last Updated: 27 June 2026

QUERYING BGPVIEW API...

AUTONOMOUS SYSTEM
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🌐 ASN Details
ASN Number—
Organization—
Country—
RIR—
AS Type—
Website—
📊 Routing Stats
IPv4 Prefixes—
IPv6 Prefixes—
BGP Peers (IPv4)—
BGP Peers (IPv6)—
IXPs—
BGP.he.net—
📝 Announced IPv4 Prefixes (top 10)
🔗 Upstream Peers
Autonomous System Numbers are the invisible backbone of global internet routing. Every time you load a webpage, your data travels across multiple ASNs — each representing a different network operator, with BGP exchanges determining the path it takes. Understanding ASNs unlocks deeper insight into how the internet actually works.

What is an Autonomous System Number (ASN)?

An Autonomous System (AS) is a collection of IP networks and routers under the control of a single organization that presents a common routing policy to the internet. Each AS is identified by a unique Autonomous System Number — a numeric identifier assigned by one of the five Regional Internet Registries (RIRs).

The concept was formalized in RFC 1930 (1996) and later updated by RFC 6996. Original 2-byte ASNs supported values from 1 to 65535. RFC 4893 extended this to 4-byte (32-bit) ASNs, supporting up to 4,294,967,295 — necessary as internet growth outpaced the original numbering space.

How ASN Lookup Works

1

Query RDAP/WHOIS

The lookup queries the appropriate RIR's RDAP (Registration Data Access Protocol) endpoint to retrieve registration metadata — organization name, country, abuse contacts, and assigned IP blocks.

2

BGP Routing Data

BGP prefix tables are queried via APIs like BGPView, RIPE Stat, or route servers to retrieve the list of IP prefixes the ASN is currently announcing to the global routing table.

3

Peer Discovery

Peering data from Internet Exchange Points (IXPs) and route collectors is analyzed to determine which other ASNs this AS exchanges routing information with directly.

4

Aggregate & Display

All data is aggregated and presented in a structured format showing the complete routing profile of the autonomous system.

ASN vs IP Address vs CIDR: Key Differences

ConceptWhat It IdentifiesExampleAssigned By
IP AddressSingle device/connection8.8.8.8ISP / RIR
CIDR BlockRange of IP addresses8.8.8.0/24RIR
ASNEntire network operatorAS15169RIR
BGP RoutePath between ASNsAS15169 → AS3356Network operators

Types of Autonomous Systems

🔍
Stub AS
Connected to only one upstream provider. Most small businesses and organizations. Traffic enters/exits through a single ISP relationship.
🔢
Multihomed AS
Connected to multiple upstream providers for redundancy. Uses BGP to choose optimal paths and maintain connectivity if one upstream fails.
🌐
Transit AS
Carries traffic between other ASNs. Tier-1 networks like AT&T (AS7018), Lumen (AS3356), and NTT (AS2914) are transit providers for the internet backbone.
📡
IXP AS
Internet Exchange Points have their own ASNs for the exchange infrastructure. AMS-IX (AS1200), LINX (AS5459), and DECIX (AS6695) are major examples.

The Five Regional Internet Registries (RIRs)

RIRRegionASN RangeWebsite
ARINNorth America1–1999, 6000–6999arin.net
RIPE NCCEurope, Middle East, Central Asia2000–2999, 5000–5999ripe.net
APNICAsia-Pacific4000–4999, 7000–7999apnic.net
LACNICLatin America & Caribbean10000–27999lacnic.net
AFRINICAfrica36864–37887afrinic.net

Real-World Use Cases

🛡️
Security Investigation
Block entire ASNs known for abuse. Security teams often blocklist ASNs associated with bulletproof hosting, botnets, or repeated attack sources — more efficient than blocking individual IPs.
📊
Network Peering
ISPs and CDNs use ASN data to evaluate peering opportunities, negotiate traffic agreements, and optimize routing paths between networks.
💡
Fraud Detection
E-commerce and fintech platforms flag transactions from datacenter or VPN ASNs as higher risk. A residential ISP ASN suggests a real human; a cloud provider ASN suggests automation.
👁
Competitive Intelligence
Analyze competitor infrastructure. Understanding which ASNs a company peers with reveals their hosting strategy, CDN choices, and geographic distribution.
🔒
Compliance & Geo-restriction
Content licensing and regulatory compliance often require restricting access by country. ASN-to-country mapping provides a reliable mechanism for regional access control.
🔨
BGP Hijacking Detection
Security researchers monitor unexpected changes in BGP routing tables. If an ASN suddenly announces IP prefixes it doesn't own, that signals a potential BGP hijack attack.

BGP and ASN: How Internet Routing Works

The Border Gateway Protocol (BGP) is the routing protocol that connects autonomous systems. When you type a URL, your request travels through multiple ASNs — each making independent routing decisions based on BGP routing tables that list which networks can be reached through which neighboring ASNs.

BGP operates on a path-vector model: each ASN advertises which networks it can reach, and which AS path the traffic must traverse to get there. This allows internet routing to be decentralized — no single authority controls global routing; instead, thousands of ASNs collectively maintain a distributed routing table through bilateral and multilateral BGP peering agreements.

Key BGP attributes that influence routing decisions include: AS Path (shorter paths are generally preferred), Local Preference (internal preference for outbound routes), MED (Multi-Exit Discriminator, used to influence inbound routing), and Community tags (used to signal routing policies between peers).

ASN Lookup vs IP Lookup vs WHOIS: When to Use Which

NeedBest ToolWhy
Where is this IP located?IP LookupReturns geolocation, ISP, city-level data
Who owns this domain?WHOIS LookupReturns domain registrant, registrar, expiry
Who operates this network?ASN Lookup (this tool)Returns routing organization, BGP peers, prefixes
Is this IP blacklisted?Blacklist CheckChecks against 15+ spam/abuse databases
What DNS records exist?DNS LookupReturns A, MX, TXT, NS, SOA records
What is the reverse hostname?Reverse DNSReturns PTR record for an IP address

Famous ASNs Worth Knowing

ASNOrganizationNotable For
AS15169Google LLCGoogle Search, YouTube, Gmail infrastructure
AS13335CloudflareCDN, DNS (1.1.1.1), DDoS mitigation
AS16509Amazon.com (AWS)AWS cloud infrastructure globally
AS8075Microsoft AzureAzure cloud and Microsoft services
AS32934Meta (Facebook)Facebook, Instagram, WhatsApp
AS2914NTT CommunicationsTier-1 global transit provider
AS3356Lumen (CenturyLink)Major US/global backbone transit
AS7018AT&T ServicesLarge US telecom backbone
AS45609Bharti AirtelMajor Indian telecom provider
AS55836Reliance JioIndia's largest mobile ISP

2-Byte vs 4-Byte ASNs

The original ASN specification used 16-bit (2-byte) numbers, supporting 65,535 unique ASNs. As internet growth accelerated and ASN exhaustion became a concern, RFC 4893 (2007) extended ASNs to 32-bit (4-byte) format, expanding capacity to over 4.2 billion.

The transition required backward-compatibility mechanisms. The "AS_TRANS" value (AS23456) was used as a placeholder in 2-byte-only BGP sessions when a 4-byte ASN needed to be represented. Modern BGP implementations universally support 4-byte ASNs, but the legacy 2-byte range (1–65535) remains in active use.

Private ASNs (64512–65534 for 2-byte; 4200000000–4294967294 for 4-byte) are used for internal routing within organizations and are never announced to the public internet — similar to RFC 1918 private IP addresses.

BGP Hijacking: When ASN Routing Goes Wrong

BGP hijacking occurs when a malicious or misconfigured ASN announces IP prefixes it does not legitimately own. Because BGP relies on trust between peers rather than cryptographic verification, a false announcement can propagate globally before operators notice, rerouting internet traffic through the attacker's network.

Notable incidents include the 2010 China Telecom routing incident (AS4134 announced approximately 50,000 IP prefixes belonging to other organizations, briefly rerouting US military and government traffic), and the 2018 BGP hijack of Amazon's Route 53 DNS service that enabled cryptocurrency theft.

RPKI (Resource Public Key Infrastructure) is the emerging solution — it cryptographically binds IP prefixes to their legitimate ASNs, enabling route origin validation that can detect and reject hijacked announcements.

How to Use This ASN Lookup Tool

1

Search by ASN Number

Enter an ASN directly (e.g., "AS15169" or just "15169"). The tool queries BGPView's API to retrieve registration details, prefix announcements, and peer information.

2

Search by Organization Name

Don't know the ASN? Search by organization name to find all ASNs registered to that entity. Large organizations like Google or Amazon may operate multiple ASNs.

3

Search by IP Address

Enter any IP address to discover which ASN it belongs to — useful when investigating a specific IP and wanting to understand the entire network organization behind it.

4

Analyze Results

Review the announced prefixes to understand the network's size, check peer count for network connectivity, and use the BGP.he.net link for deeper routing analysis.

Related Tools

🔍
IP Lookup
Full geolocation, ISP & ASN for any IP
🔎
WHOIS Lookup
Domain owner & registration details
🗄️
DNS Lookup
Query all DNS record types
🛡️
Blacklist Check
Check IP against 15+ abuse lists
📋
Bulk IP Lookup
Lookup 20 IPs at once
🔁
Reverse DNS
PTR records & FCrDNS verification

ToolsNovaHub tools are built and independently maintained with a focus on accurate, no-signup network and security utilities. Spotted an error? Let us know.

🎓
Expert Tip
DNS and mail records can take up to 48 hours to fully propagate — if ASN Lookup shows an unexpected result right after a change, wait and re-check before assuming misconfiguration.
⭐
ToolsNovaHub Pro Tip
Run ASN Lookup from more than one network (office Wi-Fi + mobile data) to rule out local resolver caching before reporting a bug.
⚠️
Common Beginner Mistake
Editing a live DNS or mail record without noting the previous value first. Always save the old record from ASN Lookup's output so you can roll back instantly if something breaks.

📋 Related Tools & Guides Comparison

ResourceTypeLink
DNS LookupNetworkOpen Tool →
DNS Propagation CheckerNetworkOpen Tool →
Reverse DNS LookupNetworkOpen Tool →
How to Debug Website Caching Issues Using HTTP HeadersGuideRead Guide →
DNS Propagation Guide: TTL, Global DNS & Migration Best PracticesGuideRead Guide →
🔗 Continue exploring: DNS Lookup · DNS Propagation Checker · Reverse DNS Lookup · How to Debug Website Caching Issues Using HTTP Headers · DNS Propagation Guide: TTL, Global DNS & Migration Best Practices · DNS vs WHOIS: Complete Comparison & When to Use Each Tool

Frequently Asked Questions

An Autonomous System Number (ASN) is a unique identifier for a network or group of networks operated by a single entity with a unified routing policy. ASNs are the fundamental identifiers of the internet's routing system — every time data travels across the internet, it passes through networks identified by ASNs, with BGP routing tables determining the path.
As of 2026, there are approximately 100,000+ active ASNs globally. The original 2-byte format supported 65,535 ASNs, and the 4-byte extension supports over 4.2 billion — providing ample space for future internet growth.
Yes. You need to apply through the RIR serving your region. Requirements typically include demonstrating a genuine need for unique routing policy (not met by using your ISP's ASN), having at least two upstream BGP connections, and paying annual fees to the RIR.
Public ASNs (1–64511 in 2-byte space) are globally unique and used for routing on the public internet. Private ASNs (64512–65534 for 2-byte; 4200000000–4294967294 for 4-byte) are for internal use only, similar to RFC 1918 private IP addresses — they are never announced to the global routing table.
This tool queries BGPView's public API (bgpview.io) for ASN registration data, prefix announcements, and peer information. BGPView aggregates data from RIPE NCC, Route Views, and other public route collectors to provide accurate, near-real-time BGP routing information.
Some ASNs aggregate their prefixes into larger CIDR blocks before announcement, reducing the total count visible in BGP tables. Others may have recently changed their routing configuration. BGP route filtering and aggregation policies vary significantly between network operators.
A BGP peer is another ASN with which this AS has established a direct BGP session to exchange routing information. Peers can be upstream transit providers (who carry traffic to/from the internet), downstream customers, or settlement-free peers at IXPs.
An Internet Exchange Point (IXP) is a physical network facility where different ASNs connect to exchange traffic directly — bypassing upstream transit providers. IXPs reduce latency, lower costs, and improve resilience. Major IXPs include AMS-IX (Amsterdam), LINX (London), DE-CIX (Frankfurt), and JPNAP (Tokyo).
RPKI (Resource Public Key Infrastructure) uses cryptographic certificates to validate that an ASN is authorized to announce specific IP prefixes. Route Origin Authorizations (ROAs) are published in the RPKI repository and validated by participating routers, blocking illegitimate prefix announcements that could indicate BGP hijacking.
Yes. Many firewalls and security platforms support ASN-based blocking. This is more efficient than blocking individual IPs when an entire network organization is the source of unwanted traffic — blocking an ASN simultaneously blocks all current and future IP addresses announced by that organization.
BGP hijacking occurs when an ASN announces IP prefixes it doesn't legitimately own, potentially rerouting internet traffic through the hijacker's network. This can be malicious (for traffic interception) or accidental (configuration errors). RPKI and route filtering are primary defenses.
Use our IP Lookup tool on your public IP address — the result will include your ASN and ISP name. Alternatively, check your ISP's technical documentation or query a BGP looking glass for your IP's route announcement.
Large organizations often use multiple ASNs for different business units, geographic regions, or service types. Google, for example, operates AS15169 (core infrastructure), AS36040 (YouTube), AS36384 (Google Fiber), and several others — allowing independent routing policies for each division.
AS_PATH is a BGP attribute that records the sequence of ASNs a route has traversed. It serves two purposes: loop prevention (if an AS sees its own ASN in the path, it rejects the route) and path selection (shorter AS paths are generally preferred, all else being equal).
Yes. ToolsNovaHub's ASN Lookup is 100% free with no account required. All queries go directly from your browser to BGPView's public API — nothing is logged on our servers.
Marketers use ASN data to filter bot traffic from analytics. Traffic from datacenter ASNs (AWS, Azure, Google Cloud) is typically non-human crawlers or scrapers, while residential ISP ASNs indicate real users. This segmentation improves the accuracy of conversion rate analysis and ad targeting.