4 ms·

Just realised something; I've been developing web applications for a relatively long time now. Maybe in the last 10 years, I had my IP addresses stored in data

by eknkc 11y ago

Just realised something; I've been developing web applications for a relatively long time now. Maybe in the last 10 years, I had my IP addresses stored in databases etc in IPv6 aware types just in case we had an IPv6 deployment in future. Better be ready. Last month, I was working on something that needed to store IP logs. I packed them in 32 bit unsigned integers. Was not a well thought decision. I think I don't care anymore, just gave up. Anyone doing the opposite of that? Maybe I was naive to jump on the train that early and these are better times. Felt like that 5 years ago too though.

geocar 11y ago
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.
- IanCal 11y ago
  > 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/ http://preshing.com/20110504/hash-collision-probabilities/ Depends on your application as to whether this is a problem or not.
  - geocar 11y ago
    50% chance of one collision. Be careful with those maths!
    - IanCal 11y ago
      Yes, thanks for the clarification, it's what I meant with "a collision" but I realise that's ambiguous.
      - geocar 11y ago
        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.
    - nly 11y ago
      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).
      - geocar 11y ago
        You're absolutely right, but it won't let me edit it. Thanks!

by eknkc 11y ago

geocar 11y ago

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.

IanCal 11y ago
> 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/ http://preshing.com/20110504/hash-collision-probabilities/ Depends on your application as to whether this is a problem or not.
- geocar 11y ago
  50% chance of one collision. Be careful with those maths!
  - IanCal 11y ago
    Yes, thanks for the clarification, it's what I meant with "a collision" but I realise that's ambiguous.
    - geocar 11y ago
      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.
  - nly 11y ago
    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).
    - geocar 11y ago
      You're absolutely right, but it won't let me edit it. Thanks!