ASN
Autonomous System Number — the identifier of the network that owns an IP range, and a primary classification signal.
An Autonomous System Number identifies a network that controls a block of IP addresses and announces routes for it. Every public address belongs to an autonomous system, and that ownership is public information.
#Why it decides how you are treated
Classification of an address usually starts with its ASN. An address announced by a residential broadband operator is treated as consumer traffic; one announced by a cloud platform is treated as infrastructure. This single lookup is what separates residential from datacenter in practice — not the physical location of the hardware.
#What ASN targeting gives you
Some providers let you select exits by ASN rather than only by country. That is useful when a target behaves differently per carrier, when you need to reproduce a specific network’s view of a service, or when one operator in a country performs noticeably better than the rest.
#Checking an address
Any IP lookup service reports the ASN, usually formatted as AS3320 followed by the operator name. It is the first thing to check when a supposedly residential address behaves as though it were flagged.
#What the number actually identifies
An autonomous system number identifies a network under one routing policy, not a company and not a place. One organisation may hold many, and a single number may cover addresses in several countries. RFC 6793 extended the space to four octets because the original two-octet space ran out.
For proxy work the number matters because it is the coarsest and cheapest classification available. A defence can decide how to treat an address from its ASN alone, before observing any behaviour. This is why a whole category of addresses can be refused at once.
#Checking an address
# Which network announces this address, and who holds it?
whois -h whois.cymru.com " -v 203.0.113.10"Read two fields. The organisation name tells you whether the range belongs to a consumer ISP or a hosting company, which decides how it is classified. The number itself tells you how much of a pool is really independent.
#Why network diversity beats address count
| Pool shape | Effect of one classification decision |
|---|---|
| Many addresses, few networks | Most of the pool is removed at once |
| Fewer addresses, many networks | A single decision removes a small share |
Count distinct networks, not distinct addresses, when you assess a pool. The second number is the one that predicts how it fails.