How to find which ISP and ASN an IP address belongs to

What is an ASN, and why does it matter for ISP proxies?

An autonomous system number (ASN) identifies a network that announces blocks of IP addresses to the rest of the internet. Every public IP is announced by at least one AS, and the AS has a registered holder, such as "AT&T Enterprises" for AS7018 or "Comcast Cable Communications" for AS7922.

Websites and IP-type databases use that holder to classify an address as a consumer provider, a business network or a hosting company. An ISP proxy is valuable because its AS holder is a consumer provider; you can verify that yourself in a minute.

Way 1: the RIPEstat API (any IP, any region)

RIPEstat is run by RIPE NCC and covers the whole internet, not only Europe. Its network-info call returns the announcing AS for an IP, and as-overview returns the holder name:

curl -s "https://stat.ripe.net/data/network-info/data.json?resource=203.0.113.10"
curl -s "https://stat.ripe.net/data/as-overview/data.json?resource=AS7018"

Way 2: whois (who registered the block)

whois asks the regional registry (ARIN for most US addresses) who registered the block. The answer can name the provider, or a business customer the provider assigned the block to. Run whois 203.0.113.10 on macOS or Linux, or use ARIN’s web search at search.arin.net. When whois and the routing data disagree, the routing data (Way 1) is what most websites use.

Way 3: one script for many IPs

If you rent 10 or 100 IPs, check them in one pass. This Node.js script (version 18 or later, no packages) prints the announcing AS and holder for each address in a list:

const ips = ['203.0.113.10', '203.0.113.11'];

async function lookup(ip) {
  const net = await (await fetch(`https://stat.ripe.net/data/network-info/data.json?resource=${ip}`)).json();
  const asn = net.data.asns[0];
  if (!asn) return `${ip}\tnot announced`;
  const ov = await (await fetch(`https://stat.ripe.net/data/as-overview/data.json?resource=AS${asn}`)).json();
  return `${ip}\tAS${asn}\t${ov.data.holder}`;
}

(async () => {
  for (const ip of ips) console.log(await lookup(ip));
})();

Which AS numbers do the main US providers use?

Our provider pages list them with their IPv4 counts (RIPEstat, October 18, 2026). The main ones: AT&T AS7018, Comcast AS7922, Verizon AS701, Spectrum AS20115 and regional networks, Cox AS22773, Frontier AS5650, Lumen (CenturyLink) AS209, Windstream AS7029 and Astound (RCN) AS6079.