ASN Lookup

Find organizational details, routing profiles, and peer information for any Autonomous System Number (ASN).

About Autonomous Systems (ASN)

The Internet is basically a network of networks. An Autonomous System (AS) is a massive network or group of networks under a single administrative authority, like an Internet Service Provider (Comcast), a university, or a large tech company (Google, Cloudflare).

Every AS is assigned a unique number mathematically tying them together via the Border Gateway Protocol (BGP). These Autonomous System Numbers (ASNs) are what routers use to figure out how to bounce traffic across the globe. Google, for example, heavily leverages AS15169 for its primary routing.

Our ASN Lookup identifies the autonomous system that routes any IP address, returning the AS number, the organisation operating it, and the address prefixes it announces. ASN data is often more revealing than geolocation when you need to understand where traffic really comes from.

What is an ASN?

An Autonomous System is a collection of IP networks operated under a single routing policy by one organisation. Each is assigned a globally unique Autonomous System Number.

Autonomous systems are how the internet routes traffic between networks. BGP, the Border Gateway Protocol, is the mechanism by which each AS announces which address prefixes it can reach, and those announcements propagate across the internet so every network learns how to reach every other.

An ASN identifies an operator rather than a location. AS15169 is Google, AS16509 is Amazon, AS13335 is Cloudflare. Knowing that an address sits in a particular AS tells you what kind of network it belongs to — a cloud provider, a consumer ISP, a university, a national carrier — which is frequently the most useful thing you can learn about it.

A network operated under a single routing policy
Identified by a globally unique number assigned by a registry
BGP announcements are how autonomous systems exchange reachability
Identifies the operator, not a geographic location
Reveals whether an address is cloud, consumer, corporate or carrier

Why ASN Data Matters

For traffic analysis, the ASN usually tells you more than the city name. Knowing that requests come from a cloud provider AS immediately tells you they are from rented servers rather than residential users — which is the more actionable distinction when assessing whether traffic is automated.

ASNs also provide a practical blocking granularity between a single address and an entire country. Attack traffic often originates from a handful of hosting providers, and rate limiting or challenging by AS is more precise than geographic blocking and far harder to evade than blocking individual addresses.

They matter operationally too: BGP hijacking, where one AS announces prefixes belonging to another, is a real and recurring internet incident with serious consequences.

Distinguishes cloud and hosting traffic from residential users
Provides a useful blocking granularity between single IP and country
Harder to evade than IP-level blocking, since changing AS means changing provider
Reveals the upstream provider when a direct abuse contact is unresponsive
BGP hijacking between autonomous systems is a recurring internet risk

How This ASN Lookup Works

The tool maps the address to the autonomous system currently announcing it.

Validates the input, accepting an IP address or an AS number
Determines which autonomous system announces the containing prefix
Retrieves the AS number and the operating organisation
Returns the announced prefix covering the address
Reports the registry and country of the AS registration

How to Use the ASN Lookup

Enter an IP address, or an AS number in the form AS15169
Run the lookup to retrieve the routing information
Review which organisation operates the autonomous system
Note the announced prefix, which shows the block being routed
Use the AS type to judge whether the traffic is hosting, consumer or corporate

Understanding Your ASN Results

The lookup describes the routing entity responsible for the address:

Field / Value	Meaning
`AS number`	The globally unique identifier, written as AS followed by digits. 32-bit numbers are now standard, having replaced the original 16-bit space.
`Organisation`	The entity operating the autonomous system. The most immediately useful field, since it tells you whether this is a cloud provider, ISP, university or corporation.
`Announced prefix`	The address block containing the queried address, as announced in BGP. It may be broader or narrower than the WHOIS allocation.
`Registry`	Which regional internet registry assigned the AS number, indicating the broad region of registration.
`Hosting AS`	An autonomous system operated by a cloud or hosting provider. Traffic from these is from servers, not residential users, which matters for bot assessment.
`Transit AS`	A carrier network that routes traffic on behalf of others. Appears in traceroute paths rather than as the origin of traffic.
`Origin AS`	The autonomous system that originates the announcement for this prefix. Where the address genuinely lives, as opposed to networks merely carrying its traffic.

Common Problems & How to Fix Them

This is normal where address space is sub-allocated. The WHOIS record may name a customer holding the block while the ASN shows the provider actually routing it.

Both are useful. The WHOIS organisation is who holds the allocation; the ASN organisation is who has the technical ability to act. When an abuse contact is unresponsive, the upstream AS operator is often the more effective escalation.

Multiple origin AS announcements for the same prefix can be legitimate, as in anycast deployments, or can indicate a BGP hijack.

Check whether the announcing autonomous systems have a plausible relationship. A prefix suddenly announced by an unrelated AS in a different region is a hijack indicator worth investigating through public BGP monitoring data.

Automated traffic, scraping and attack attempts disproportionately originate from cloud and hosting autonomous systems.

Rate limiting or challenging by AS is more precise than geographic blocking. Be careful though: legitimate services, monitoring tools and corporate VPNs also run on the same infrastructure, so an outright block will catch real users.

The address may be in private space, reserved space, or a block not currently announced in the global routing table.

Check whether it falls in a private range such as 10.0.0.0/8 or 192.168.0.0/16, or reserved documentation ranges. An allocated but unannounced block is simply not routable from the public internet.

Best Practices

Use ASN data alongside geolocation, since it is often the more informative signal
Check the AS type before interpreting traffic patterns
Escalate abuse to the upstream AS operator when a direct contact is unresponsive
Prefer AS-level rate limiting over country-level blocking
Compare the ASN organisation against the WHOIS organisation for sub-allocated space
Monitor BGP announcements for your own prefixes to detect hijacking
Remember legitimate services also run on hosting autonomous systems

Security Recommendations

Treat traffic from hosting autonomous systems as automated by default and apply proportionate verification
Monitor public BGP data for unauthorised announcements of your own prefixes, which is how hijacks are detected
Deploy RPKI route origin validation so other networks can verify your announcements are legitimate
Be aware that some autonomous systems are known for tolerating abusive customers, which is useful context when assessing traffic
Avoid blocking entire autonomous systems belonging to major cloud providers, since that excludes substantial legitimate traffic
Use ASN data to identify the responsible party during incident response rather than relying on geolocation

Frequently Asked Questions

An Autonomous System Number uniquely identifies a network operated under a single routing policy. It identifies an operator — a cloud provider, ISP, university or corporation — rather than a geographic location.

An IP address identifies a single host. An ASN identifies the entire network that routes a whole set of address blocks. One autonomous system may announce thousands of prefixes containing millions of addresses.

Because it tells you what kind of network the traffic came from. Knowing an address sits in a cloud provider AS means the traffic is from a rented server, which is far more actionable than knowing which city a database associates with it.

When one autonomous system announces address prefixes belonging to another, causing traffic to be routed to the wrong network. It can be a configuration error or deliberate interception, and it remains a recurring internet incident.

Rate limiting or challenging by AS is often more precise than country blocking. Outright blocking is risky for major cloud providers, since legitimate services, monitoring tools and corporate VPNs run on the same infrastructure.

Resource Public Key Infrastructure, a cryptographic system letting address holders declare which autonomous systems may announce their prefixes. Networks validating against it can reject hijacked announcements, which is the main structural defence against BGP hijacking.

It is probably in private space such as 10.0.0.0/8, reserved space, or a block not currently announced in the global routing table. Addresses that are allocated but unannounced are simply not routable from the public internet.