The "Net Load Class" of a PROFINET device certifies its robustness against intense network traffic (flooding, broadcast storm), with three levels (NL Class 1, 2, 3) guaranteeing that the device continues to respond correctly under real-time conditions.

Net Load Robustness is a certification of the device's ability to tolerate "noisy" Ethernet traffic without losing its PROFINET response times. It is particularly important on mixed IT/OT networks or under a DoS attack. The classes are: NL Class 1 (minimum robustness, around 5 Mbit/s of broadcast); NL Class 2 (standard level, around 50 Mbit/s); NL Class 3 (high level, up to 100 % of the link bandwidth). The NL Class of a device should be checked whenever it is integrated on a shared network.

If you plan to share the same physical Ethernet between PROFINET and general IT traffic, target devices certified at NL Class 2 or above; NL Class 1 hardware can stop responding under a moderate broadcast storm.