Distributed virtual security appliance and flow-based forwarding system using virtual machines

A method performed by a network system having a plurality of processing units implemented using a plurality of respective virtual machines, includes: receiving a first packet at a first virtual machine of the plurality of virtual machines, wherein the first virtual machine is configured to receive the first packet from a network through an interface and has session processing capability; calculating a first value using a mathematical algorithm based on one or more information regarding the first packet; and using the calculated first value to identify a second virtual machine of the plurality of virtual machines in the network system.