In an environment where FlowVisor is implemented, flows in each slice of the topology must be confined to their respective flowspaces. Message rewriting is the technique used by FlowVisor to ensure that flows in one slice do not interfere with those in other slices. There are instances where the rules cannot be rewritten to suite a particular slice; such occurrences lead to the FlowVisor sending an error message to the controller that such a flow entry cannot be injected into the flowspace.