How about this: Server-wide salt. Randomly generated every 24h or server reboot (whichever is sooner). The salt is not saved alongside the hashed IP, it is no

How about this: Server-wide salt. Randomly generated every 24h or server reboot (whichever is sooner). The salt is not saved alongside the hashed IP, it is not saved anywhere whatsoever. There is no log of previous salts. You can still track a user session across multiple page calls, but the hash can not track them across different sites.