:format(webp))
An ASN (Autonomous System Number) identifies which network operator — an ISP, a hosting company, a mobile carrier — a given IP address belongs to. Anti-bot systems check the ASN before almost anything else, because it instantly reveals whether traffic is coming from an ordinary home connection or a known hosting provider, regardless of how the rest of the request looks. That single lookup is why datacenter IPs get flagged categorically and residential IPs generally don't.
What an ASN actually is
An Autonomous System Number identifies a distinct network on the internet — a collection of IP address ranges under the control of one organization, with its own routing policy. Every ISP, mobile carrier, cloud provider, and large company running its own network has at least one ASN, assigned by a regional internet registry. When your traffic reaches a website, the site doesn't just see your IP address; a quick lookup also reveals which ASN that IP belongs to, which is effectively an answer to "whose network is this."
Why this is the first thing anti-bot systems check
An ASN lookup is fast, cheap, and doesn't require analyzing any behavior at all — which is exactly why it's usually the first filter a detection system applies, before looking at headers, request patterns, or anything else. Datacenter and hosting-provider ASNs are well documented and easy to maintain a blocklist against, since legitimate residential internet traffic essentially never originates from them. An IP sitting in a known hosting range gets treated with suspicion immediately, independent of how well-crafted the rest of the request is.
Residential and mobile IPs sit in ASNs registered to actual internet service providers and mobile carriers — the same networks real home and phone connections use. That's the structural reason residential proxies clear this first checkpoint that datacenter IPs don't: the ASN itself looks exactly like the ordinary consumer traffic a site expects to see.
Where "mislabeling" comes from
Some providers label an IP "mobile" or "residential" based on marketing rather than what an ASN lookup actually shows. A quick ASN check reveals the real story — an IP claimed to be mobile but sitting in a datacenter ASN isn't providing the detection resistance genuine mobile routing does. This is worth checking directly rather than taking a label at face value; it's covered in more depth in 10 Proxy Myths, Debunked.
Targeting by ASN directly
Because ASNs map to specific network operators, they're also directly useful beyond detection avoidance — mainly for testing how a site or app behaves on a specific ISP's network, which matters for things like CDN routing, ISP-level throttling, or regional network quirks that vary carrier to carrier.
bash
# Chicago, pinned to a specific ISP (AT&T, ASN 7018)
curl -x "http://login:country-us-city-chicago-asn-7018@ip.simplynode.io:9003" \
"https://target.example.com/page"Combining city and ASN targeting is useful when a site's behavior depends on both location and carrier — some content delivery and rate-limiting decisions are made per-ISP, not just per-region, so testing from the right city on the wrong ISP can still miss the specific case you're checking for.
What this means practically
You don't need to think about ASNs for most day-to-day proxy use — pick residential or mobile, set a country, and the ASN-level advantage is already built in. It matters when: you're troubleshooting why a datacenter proxy gets blocked instantly while a residential one on the same request doesn't; you're verifying a provider's "mobile" claim is real; or you specifically need to test from a named ISP rather than just a named country.
FAQ
What's the difference between an IP address and an ASN? An IP address is a single address; an ASN identifies the entire network — the ISP, hosting company, or carrier — that IP address belongs to. Millions of IPs can share the same ASN.
Why do datacenter proxies get blocked more than residential ones? Detection systems check the ASN an IP belongs to before evaluating anything else. Datacenter and hosting-provider ASNs are well-documented and easy to flag categorically; residential ISP ASNs carry the same profile as ordinary consumer internet traffic.
Can I target a proxy by ASN directly? Yes, where a provider supports it — you can specify an ASN alongside country and city parameters to test from a specific ISP's network rather than just a general region.
How can I tell if a "mobile" proxy is actually routing through a mobile network? An ASN lookup on the IP reveals the actual network it belongs to. If it resolves to a datacenter or hosting ASN rather than a mobile carrier's ASN, it isn't providing genuine mobile-network routing regardless of how it's labeled.