In enterprise networks, policies (e.g., QoS or security) are often defined based on the categorization of hosts along dimensions such as the organizational role of the host (faculty vs. student), and department (engineering vs. sales). While current best practices (VLANs) help when hosts are categorized along a single dimension, policy may often need to be expressed along multiple orthogonal dimensions. In this paper, we make three contributions. First, we argue for Attribute-Carrying IPs (ACIPs), where the IP address allocation process in enterprises considers attributes of a host along all policy dimensions. ACIPs enable flexible policy specification in a manner that may not otherwise be feasible owing to the limited size of switch rule-tables. Second, we present Alpaca, algorithms for realizing ACIPs under practical constraints of limited-length IP addresses. Our algorithms can be applied to different switch architectures, and we provide bounds on their performance. Third, we demonstrate the importance and viability of ACIPs on data collected from real campus networks.