Some embodiments of the present invention provide a system for packet classification and spreading in a virtualized system. The system can use information in a packet's header to determine a destination system-image in the virtualized system, and a packet-spreading policy for the destination system-image. The system can determine a key using the information in a packet's header. Alternatively, the system can hash the information in the packet's header to obtain an index value. Next, the system can use the key or the index value to perform a lookup in a table which associates keys or index values with system images and/or packet-spreading policies. Once the destination system-image and the packet-spreading policy are determined, the system can deliver the packet to a thread on the destination system-image according to the packet-spreading policy.