I do not know if this is documented anywhere, but I can tell you what I do. As long as the IPS 4200 has power, with the right software settings, the unit can fail such that it will pass traffic. Should the unit loose power, it does stop all traffic. I run a patch cable in parallel with the in line IPS unit, in the same VLAN, with a higher STP cost. Thus all traffic will traverse the IPS unit when possible, but should something happen to it, a $10 patch cable takes over.

Mike