Prevent Unauthenticated Users to vote like multiple times in ASP.Net

Hi, How can we prevent non ahuthenticated users from like and dislike multiple times? one way : save Ip address in a cookie but theres's two problem 1. I heard Ip address isn't unique and changes frequently 2. cookie can be deleted by user I'd like know what's your suggestion and what's the common method for it? thanks a lot