I have Intrushield 3000 appliance.I have also fail open kit.How to configure IPS with fail open kit (physical cable connection with IPS-fail open kit and system configuration in Intrushield 3000 for fail open.
Besides the KB that Bruno refers, I will tell you my personal experience with FOK:
1) If you are working with Gigabit speeds please read attached KB, Gigabit and Fail Open Considerations item.
2) In FOK there is a white LED that indicates comunication between sensor and FOK. That LED won´t turn on until you put ports in "Enable".