Methods, systems, and apparatus, include computer programs encoded on a computer-readable storage medium, and include a method for providing content. The method includes receiving a request for content from a requesting device that includes an associated IP address and determining that the received request is appropriate for clustering based on the IP address. The method further includes determining whether the received request is already associated with a cluster including, and when not, returning a cluster cookie to the requesting device and storing cluster information including the IP address associated with the requesting device; otherwise creating a cluster including returning a cluster cookie to the requesting device and storing in a data set associated with the cluster information including the IP address associated with the requesting device. The method further includes providing a response to the received request based on the data set for an associated cluster.