An example system includes: at least one memory; programmable circuitry; and instructions to cause the programmable circuitry to: cache a first ordered list of internet protocol (IP) addresses in a domain name system (DNS) cache; cache a second ordered list of IP addresses in the DNS cache; access a first server identifier from a first server associated with the first ordered set of IP addresses; access a second server identifier from a second server associated with the second ordered list of IP addresses; hash the first and second server identifiers to generate a user identifier; and store the user identifier as a cookie.