US Patent 10237172 Using headerspace analysis to identify flow entry reachability

Some embodiments provide a method that uses headerspace analysis. The method receives several flow entries for distribution to a set of forwarding elements that implement a logical network. The method models each of the flow entries as a function that operates on a representation of a packet header. The method uses the modeled functions to identify a set of paths from a packet source to a packet destination. For each particular path of the identified paths, the method uses inverses of the modeled functions to determine a set of packet headers. Packets sent from the packet source with any packet header in the set of packet headers follow the particular path through the flow entries.