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How to blacklist the "prefix" of IPv6

id flag

With IPv4 it is pretty easy to blacklist IPs since it's not cheap to get new IPs and they are limited. However, with IPv6 it's pretty easy/free to generate a huge amount of unique IPs and it's pretty hard to blacklist some user based on his/her IPv6.

After researching about this, I discovered that there is some part in the IPv6 that is not very easy to the user to change (/64) and there is some part in the IPv6 that IS easy to change (/64) = 64 + 64 = 128 bits.

So I assume, half of the address can be changed easily and half cannot, right? So take this IPv6 example:

  2001:0db8:85a3:0000:0000:8a2e:0370:7334

If I want to block this user, should I block all the IPs starting with "2001:0db8:85a3:0000" or the ones ending with "0000:8a2e:0370:7334"? Which part is the hard to change and which one is the easy?

In case I am talking some nonsense here, please correct me! I am completely new to this IP stuff :)

djdomi avatar
za flag
just block 2001:0db8:85a3::/64
djdomi avatar
za flag
Does this answer your question? [How does IPv6 subnetting work and how does it differ from IPv4 subnetting?](https://serverfault.com/questions/426183/how-does-ipv6-subnetting-work-and-how-does-it-differ-from-ipv4-subnetting)
id flag
@djdomi I need to work with substrings in the blacklist. So you say I should block "2001:0db8:85a3:0000"? Blocking all the IPs the match the first 64 bits? If you post a simple answer I will be glad to accept it. I read the link you provided, is very clear but there is no place where it says what part explicitly of the IPv6 the user can freely change.
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