Are you referring to a local instance, or are trying to check if people access your website/content are doing so from dynamic ips? By dynamic ips, are you really wondering as to whether they are DHCP, or something else? Maybe some more information on what the intended goal would help, as you are going to have a difficult time just trying to figure out if they are bots or fake clients without more information to go on. But to help a bit with what is provided, you could utilize cookies and see if a cookie exists for a client, but with a new ip. If that is the case, and it is on a similar net, then you would know that the client is likely assigning a new ip address from the same computer.