I've done a KB search (it's good to test the KB using others requests)
KB Search Search term: Sensor Behavior. (to begin with)
Standout article - KB56085 Expected packet loss when using the Sensor Fail Open mode.
KB Search Search term: Sensor Reboot Behavior.
Conclusion and tasks: Article contains word Reboots, search fails to recognise this. Will edit article to reflect question and improve search results, I will report search findings to the rest of the KB with a view to improving the search.
Let me know if the article answers your questions.
regards Jonathan Dyton
You may loss a couple of packets as the relay kicks in to switch to fail open - most traffic won't even notice it, things like web traffic will just continue as if anything was dropped it just retries. Same when the box comes back up.
I would say that the dropped traffic depends on the size of the sensor...
In my experience if it is a large sensor with an external fail-open kit then the drop tends to not be seen at all as the external FOK takes over
If it is a smaller device with an inbuilt FOK then there will be a loss of 2-3 pings (depending on network performance)