What is an ASN? Autonomous systems, IP ASN lookups, and why they decide how proxies are scored

What is an ASN? An ASN (autonomous system number) is the unique number assigned to a network that controls its own routing on the internet: an internet provider, a cloud company, a university or a large enterprise. Every public IP address sits in a block announced by one of those networks, so looking up an IP's ASN tells you whose network the address belongs to. For proxies that lookup is decisive, because websites classify the ASN as consumer ISP, hosting, business or education and score your traffic by it.

Below: what an autonomous system is, who hands the numbers out, how to run an ASN lookup yourself with real output, what the ASN types mean, and why an ISP proxy and a datacenter proxy look different in that lookup.

#What is an ASN?

The internet is tens of thousands of independent networks that agree to carry each other's traffic. Each one that runs its own routing policy is an autonomous system (AS), a term defined in RFC 1930. To exchange routes with its neighbours over BGP, the internet's routing protocol, each needs a number: its ASN.

An AS tells the rest of the internet "these address blocks are reachable through me". Google announces 8.8.8.0/24 from AS15169. Comcast announces blocks for its home customers from AS7922. AWS announces its cloud ranges from AS16509 and several others. Look up any public IP and you find the AS announcing the block around it, and from that the organisation behind it.

A few details worth knowing:

• ASNs were 16-bit and are now 32-bit. The original range ran to 65,535. The 32-bit extension, defined in RFC 6793, raised the ceiling to about 4.29 billion, so newer networks often have numbers in the hundreds of thousands.
• Some numbers are private. 64512–65534 and 4200000000–4294967294 are reserved for private use and never appear on the public internet.
• One organisation can hold many. Large providers run separate ASNs for regions, acquisitions or product lines, so "which company" and "which ASN" are not a one-to-one match.

#Who assigns ASNs: IANA and the five RIRs

IANA hands blocks of ASNs and IP addresses to five regional internet registries, and the registries assign them to networks in their region:

Each registry keeps a public record of who holds what, queryable over whois and its modern replacement, RDAP. That record is the raw material every IP intelligence service builds on.

#How to do an ASN lookup

Four free lookups, each run on 8.8.8.8 (Google's public DNS resolver) on 2026-09-29. Swap in any public IP.

#ipinfo: ASN and name in one line

curl -s https://ipinfo.io/8.8.8.8/org

AS15169 Google LLC

The fastest check, with no account needed for occasional lookups. Drop /org from the URL for the JSON record with location as well.

#Team Cymru over whois

Team Cymru's IP-to-ASN service adds the announced prefix, the registry and the allocation date:

whois -h whois.cymru.com " -v 8.8.8.8"

AS      | IP               | BGP Prefix          | CC | Registry | Allocated  | AS Name
15169   | 8.8.8.8          | 8.8.8.0/24          | US | arin     | 2023-12-28 | GOOGLE - Google LLC, US

We sent the query to port 43 directly, which is all the whois client does; the command above is the equivalent. It also accepts a whole list in bulk mode, which matters when you are checking a batch of proxies.

#Team Cymru over DNS

If you have dig but no whois, ask over DNS. The IP goes in with its octets reversed (8.8.8.8 reads the same both ways; 203.0.113.10 becomes 10.113.0.203):

dig +short TXT 8.8.8.8.origin.asn.cymru.com
dig +short TXT AS15169.asn.cymru.com

"15169 | 8.8.8.0/24 | US | arin | 2023-12-28"
"15169 | US | arin | 2000-03-30 | GOOGLE - Google LLC, US"

The first line maps the IP to its ASN and prefix, the second names the ASN.

#RDAP: the registry's own record

RDAP returns the registry entry as JSON. rdap.org redirects each query to the right registry:

curl -sL https://rdap.org/ip/8.8.8.8 | jq '{handle, name, startAddress, endAddress, type}'

{
  "handle": "NET-8-8-8-0-2",
  "name": "GOGL",
  "startAddress": "8.8.8.0",
  "endAddress": "8.8.8.255",
  "type": "DIRECT ALLOCATION"
}

That is who the address is registered to, which is not always the same network that announces it. When the two disagree, the difference is worth understanding before you trust either.

#IP ASN types: ISP, hosting, business, education

The lookups above name the network. They do not say what kind of network it is. IP intelligence vendors add that label by classifying every ASN; ipinfo's ASN API uses five types:

Mobile carriers usually appear as ISP, and some vendors flag mobile traffic separately.

Two cautions. First, the type is a vendor's judgement, and vendors disagree at the edges. Networks also describe themselves in PeeringDB, the directory operators use to arrange interconnection, and on 2026-09-29 its API listed Comcast as "Cable/DSL/ISP", Google and Hetzner as "Content", and Amazon.com as "Enterprise". Self-description is not what a bot-protection product scores. Second, classification happens per ASN and sometimes per range, so a provider that runs both consumer access and hosting can have ranges labelled differently.

#Why websites score traffic by ASN

Bot protection has to decide in milliseconds whether a request is worth trusting, before it has seen any behaviour. The network is the cheapest signal available:

• Base rates. Most traffic from consumer ISPs is people. Most traffic from hosting networks is automated: crawlers, monitors, scripts. Starting from the ASN type gets a site most of the way on the first request.
• It costs the site almost nothing. An ASN lookup is a local database read, with no challenge, no JavaScript and no delay for real visitors.
• Reputation is collected per network. Abuse reports, spam lists and a site's own block history roll up by ASN and range, so a network with a bad record drags down every address on it.

The ASN is the first layer, not the whole score. IP history, request rate, TLS and browser fingerprint, and behaviour all follow. A clean consumer ASN will not rescue a scraper that sends fifty requests a second with a default library user agent; how to avoid getting blocked while scraping covers the layers after this one.

#ISP proxies vs datacenter proxies by ASN

Both ISP and datacenter proxies run on servers in data centres, and both are static. The ASN is what separates them:

That label is what you pay for with an ISP proxy, and many vendors charge more for it than for a datacenter IP (ProxyHive sells the two on one rate card). Either way, it only earns its keep when the target penalises hosting ASNs. If it does not, a datacenter proxy does the same job. Residential proxies also return consumer ASNs, but from rotating home connections rather than fixed server addresses; the pillar guide on residential vs ISP vs datacenter proxies compares all three.

#Check your own proxy's ASN

You do not have to take any vendor's word for what an address is. Find the exit IP through the proxy, then look it up:

EXIT=$(curl -s -x "http://USERNAME:PASSWORD@HOST:PORT" https://api.ipify.org)
curl -s "https://ipinfo.io/$EXIT/org"

Copy the host, port, username and password from your order in the dashboard at app.proxyhive.io. Then read the result:

• An ISP proxy should return the carrier the vendor named. ProxyHive ISP IPs are ordered by country, region, city and carrier, so the carrier is on the order before you pay, and this lookup confirms it.
• A hosting company's name means a datacenter address, whatever the product page called it.
• The right network in the wrong country means registry data and geolocation disagree; check where your target thinks you are before relying on it.

ProxyHive ISP proxies start at $3.20/IP a month for a single IP, and datacenter proxies at $3.20/IP, so checking an ASN on one address before you commit to more costs very little.