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I think a 32-bit hash of an IPv6 address will be fine for a long time, and remain much faster to search/sort than a 128-bit value.

I also think that if you can't upgrade your database you're going to have other problems as well.



> I think a 32-bit hash of an IPv6 address will be fine for a long time

Be careful with this, a 32 bit hash can see collisions with remarkably low numbers. A 50% chance of a collision is seen with ~75k entries: http://preshing.com/20110504/hash-collision-probabilities/

Depends on your application as to whether this is a problem or not.


50% chance of one collision. Be careful with those maths!


Yes, thanks for the clarification, it's what I meant with "a collision" but I realise that's ambiguous.


No worries, and you're absolutely right that it depends on your application whether this is a problem or not!

Estimating population sizes? "Unrecognised IP addresses?" Probably fine.

Interning the hash and using the real IP address in a database someplace? Probably not.


No, it's a 50% probability of there being at least one collision (or, put another way, a 50% chance of there being no collisions).


You're absolutely right, but it won't let me edit it.

Thanks!




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