In Bitcoin Wiki Weaknesses: Sybil attack they mention that:

"Bitcoin makes these attacks more difficult by only making an outbound connection to one IP address per /16 (x.y.0.0)".

Why would this make a Sybil attack more difficult? Is there a reason for choosing a /16 subnet or is it randomly chosen by the developers with no background? Wouldn't it be more secure to choose a smaller subnet?

1 Answer 1


When you are buying servers you can order multiple IP per one server, typically in the same /8 or /16 subnet. So 1 server can serve as 100 or even 1000 Bitcoin nodes.

Ordering lots of IPs in lots of different /16 subnets is rarely possible for the same server.

Hence this change makes it harder/more expensive to launch 1000's of rogue Bitcoin nodes - you will have to distribute them across large number of servers in different datacenters.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.