If you've ever wondered how a website decides, in the few milliseconds before it even reads your request, that you're a bot — a big part of the answer is the ASN. It's one of those pieces of internet plumbing nobody mentions until it's the reason your traffic is getting blocked.

So here's the plain-English version.

The internet is a network of networks

An Autonomous System is just a network under one administrative roof — an ISP, a cloud provider, a university, a big company. Each one gets a number, the ASN, and announces "these blocks of IP addresses belong to me" so the rest of the internet knows where to route traffic.

That's the part that matters for you: an ASN is public. Anyone can look up which network owns any IP, and what kind of network it is. AS16509 is Amazon. AS15169 is Google. AS13335 is Cloudflare. When a request lands from an address inside one of those, the destination already knows it came from a cloud network before a single header is parsed.

Why that's the whole ballgame for detection

Think about who actually sits behind each type of ASN:

• A hosting ASN (AWS, OVH, Hetzner) is full of servers. Servers scrape, servers spam, servers run bots. So traffic from there starts with a trust deficit.
• A mobile carrier ASN is full of phones — thousands of real people per IP. Blocking it means blocking customers, so sites are far more forgiving.
• A residential ISP ASN is somewhere in between: real households, harder to ban wholesale.

None of this is about your behaviour yet. It's pure reputation-by-association, decided by the name tag your IP's network is wearing. That's why swapping to a bigger pool of cloud IPs never fixes a block — they all carry the same hosting ASN, so they all inherit the same suspicion.

How to find the ASN of an IP

You don't need special access — it's public routing data. The quickest way is to paste an IP or an ASN into an ASN lookup; you'll get the owning organisation, country, registry, and whether it reads as datacenter, mobile or residential. If you just want to know what your own exit looks like right now, what-is-my-IP shows the same thing for your current connection.

On the command line, whois against Team Cymru's service does it too:

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

It'll come back telling you that 8.8.8.8 belongs to AS15169, Google. Same data, different front door.

What to do with that knowledge

Once you've internalised that the ASN is doing most of the talking, the strategy gets simple. Stop trying to out-rotate a bad category. If your exit sits in a hosting ASN, that's the problem — not your request rate, not your headers (yet). Move to a network whose ASN carries the reputation you actually want.

That's the entire reason real mobile proxies hold up: the traffic exits through a genuine carrier's ASN, so to the destination it's indistinguishable from an ordinary phone on that network. The name tag reads "real mobile user," and that changes the conversation before it starts.