request an adjacent fbcs to bypass fbcs x for future packets corresponding to flow f and send traffic to an ordered set of network functions x u2032 instead this bypass request is substituting the network function chain entry corresponding to fbcs x for a new ordered set of network function chain entries corresponding to network functions x u2032 for flow f fbcs x makes the request through the network controller that validates the request and translates the request from the abstract topology into the non abstracted topology then the network controller updates the adjacent fbcss with the substitution of network function entries associated with x u2032 for x for flow f in the case where no abstraction was provided fbcs x may send the request directly to adjacent fbcss i e bypassing the network controller for faster response at the expense of the policy validation performed by the controller fbcss maintain sub flow tables that perform the substitutions as they create the ordered set of network functions for each flow sub flow fig1 illustrates network topology of an example packet based network 10 that is referred to throughout this disclosure to help illustrate various embodiments of this disclosure fig1 shows a function chain network controller 12 a plurality of fbcss 14 that are specialized nfs that are configured to modify network function chains and other nfs 16 that do not modify network function chains as well as virtual nfs vnfs 18 that are composed of multiple network functions some of which may be a fbcs including load balancing lb functions or other functions such as deep packet inspection dpi or other fbcs functions fig1 also shows packet flows 20 before.