ASN Lookup
Query autonomous system details and IP ranges for a given ASN.
ASN Lookup
Runs entirely in your browser
This tool executes locally using standard browser APIs (for example window.crypto.getRandomValues or crypto.subtle where applicable). Your input is not transmitted to or stored on a ScriptPulse server. See How Calculations Work.
What This Tool Does
- The ASN Lookup tool resolves an IP address or Autonomous System Number to information about the network it belongs to: the owning organization, the ASN itself, and the announced IP ranges associated with it. An Autonomous System is a network or group of networks under single administrative control that presents a common routing policy to the internet — every ISP, cloud provider, university network, and large enterprise typically operates as its own AS, identified by a unique number.
- This matters day to day for more than curiosity: knowing which AS an IP address belongs to tells you which organization actually operates that address range, which is useful for investigating suspicious traffic, understanding why a route is taking a particular path, or confirming that a resolved IP genuinely belongs to the cloud provider or CDN you expect rather than an unrelated network.
- ASN data comes from BGP (Border Gateway Protocol) routing announcements — the same mechanism that determines how traffic actually gets routed across the internet — so an ASN lookup reflects real, currently-announced routing information, not just static registration records.
How It Works
- Given an IP address, the tool determines which currently-announced BGP route (CIDR block) contains it, and reports the ASN responsible for announcing that block.
- Given an ASN directly, the tool reports the organization associated with that AS number and the set of IP ranges it currently announces.
- The organization name and registration details are cross-referenced against regional internet registry (RIR) data — ARIN, RIPE NCC, APNIC, LACNIC, or AFRINIC, depending on which region originally allocated the range.
- Because BGP announcements can change (an IP range can be reassigned or re-announced by a different AS over time), results reflect currently active routing data, not a permanently fixed record.
Usage
- Enter either an IP address or an ASN (e.g. AS15169) into the lookup field.
- Run the lookup.
- Review the returned organization name, ASN, and the announced IP range(s) associated with it.
- Cross-reference the result against what you expected — for example, confirming a resolved hostname's IP genuinely belongs to the ASN of the provider it's supposed to be hosted with.
Examples
- Looking up an unfamiliar IP from a server access log and discovering it belongs to a known cloud provider's ASN, indicating likely automated scanning traffic rather than a targeted human visitor.
- Looking up AS15169 directly and confirming it corresponds to Google's public ASN and its associated address ranges.
- Confirming that a CDN-fronted domain's resolved IP falls within the CDN provider's actual announced ASN range, as a basic sanity check before trusting a redirect.
- Comparing the ASN of two IP addresses seen in the same traceroute to understand at which point traffic crosses from one network operator to another.
Real-World Use Cases
- Investigating which organization actually operates a suspicious or unfamiliar IP address seen in server logs.
- Confirming that traffic claiming to come from a known cloud provider or CDN is actually announced by that provider's real ASN, not a spoofed or unrelated source.
- Understanding routing behavior by identifying which AS a given destination or hop belongs to during network troubleshooting.
- Researching the approximate network footprint (announced IP ranges) of a specific organization or ISP.
Best Practices
- Treat ASN/organization data as a strong signal, not absolute proof of intent — a legitimate cloud provider's ASN can host both benign traffic and traffic from a bad actor who happens to be renting infrastructure there.
- When investigating suspicious traffic, combine ASN lookup with reverse DNS and WHOIS lookups rather than relying on any single signal alone — each reveals a different, complementary piece of the picture.
- Remember that BGP announcements change over time; don't assume an ASN-to-organization mapping documented months ago is still accurate for an active investigation — re-verify with a fresh lookup.
- When verifying a CDN or cloud provider claim, check the ASN of the specific resolved IP, not just the domain's registrar or hosting reputation — routing (ASN) and registration (WHOIS) are different, complementary layers of trust.
Common Mistakes
- Treating an ASN lookup result as proof of malicious or benign intent by itself — an ASN identifies the network operator, not the specific actor using an address within it.
- Confusing ASN data (which reflects current routing/BGP announcements) with WHOIS registration data (which reflects who registered the address block, sometimes with a different organization actually operating it day to day).
- Assuming a single organization operates only one ASN — large providers frequently operate multiple ASNs for different regions or business units.
- Not re-checking ASN data for time-sensitive investigations — announced ranges genuinely change hands or get re-routed, so a lookup from weeks ago may no longer reflect the current state.
Limitations
- ASN and BGP announcement data reflects the current global routing table at lookup time; it is not a permanent historical record, and past announcements aren't retrievable through this tool.
- This tool identifies the network operator responsible for routing a given address range — it cannot identify the specific individual or process behind any particular request from within that range.
- Some smaller or newly-announced ranges may have incomplete organization metadata in registry data, resulting in a correct ASN but a less descriptive organization name.
Technical Reference Guide
- Autonomous System Numbers and the Border Gateway Protocol that uses them are defined by RFC 4271 (BGP-4).
- AS number allocation and the four-byte ASN extension (since the original 16-bit space was exhausted) are specified by RFC 6793.
- Regional Internet Registries (ARIN, RIPE NCC, APNIC, LACNIC, AFRINIC) each maintain the registration records for IP and ASN allocations within their region, which is why the same lookup may reference different registries depending on where a range was originally allocated.
FAQ
What is an Autonomous System Number?
An ASN uniquely identifies a network (or group of networks) under single administrative control that presents a common routing policy to the rest of the internet via BGP — every major ISP, cloud provider, and large enterprise typically has its own.
Does an ASN lookup tell me who sent a specific request?
No — it identifies which network operator's infrastructure an IP address belongs to, not the specific individual, application, or process behind any one request from within that range.
Why might the same organization show multiple different ASNs?
Large providers frequently operate several ASNs, often split by region, business unit, or historically-acquired infrastructure that was never consolidated under one AS.
Is ASN data the same as WHOIS data?
No — ASN data reflects current BGP routing announcements (who is actually routing traffic for an address range right now), while WHOIS reflects registration records (who registered the block, which can lag behind or differ from who operates it day to day).
Can ASN data change over time for the same IP?
Yes — address ranges can be reassigned, sold, or re-announced by a different network operator, so a lookup performed today may return a different result than the same lookup performed months earlier.
Is looking up someone's ASN a privacy concern?
ASN data identifies network infrastructure ownership, which is public routing information by necessity of how the internet functions — it does not reveal personal identity, only which organization's network an address belongs to.
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