Subnet ban

A subnet ban is a block applied to an entire range of IP addresses at once, so every address in that range is refused — not only the address that misbehaved. It is a blunt instrument, and sites use it because chasing individual addresses one at a time does not scale.

How wide a range is

Ranges are written in slash notation. A /24 covers 256 consecutive addresses; a /16 covers roughly 65,000. A site that bans a /24 has taken out everything from x.x.x.0 to x.x.x.255 in one move, whether or not those addresses ever sent it a request.

Why it matters when you buy proxies

Cheap proxies are sold out of contiguous blocks. When a provider leases a /24 and rents the addresses to a hundred customers, one of those customers hammering a target can get the whole block refused — and you find out when your proxy stops working for no reason you can trace. Checking the ASN and the block a provider's addresses sit in tells you how exposed you are.

A concrete example

You buy ten datacenter proxies and they arrive as .11 through .20 of the same /24. To the target site that is not ten identities, it is one neighborhood — and one ban ends all ten at the same instant. Carrier addresses behave differently, because the range you sit in is full of real subscribers rather than other proxy customers.