Chapter 8 Hardware Acceleration : NP6 Acceleration : NP6 session fast path requirements : Mixing fast path and non-fast path traffic
  
Mixing fast path and non-fast path traffic
If packet requirements are not met, an individual packet will be processed by the FortiGate CPU regardless of whether other packets in the session are offloaded to the NP6.
Also, in some cases, a protocol’s session(s) may receive a mixture of offloaded and non-offloaded processing. For example, VoIP control packets may not be offloaded but VoIP data packets (voice packets) may be offloaded.