We accidentally ordered a load of “Generic brand” 100G QSFP from FS. Everything worked and appeared fine from the perspective of the switch and cards, reported OK status for everything, _except_ the lasers never turned on. Switching to an Extreme switch made the switch end work fine, but not the server.

Turns out Mellanox/NVIDIA hardware are _really_ picky about their cards. We bought a box from FS that reprogrammed the compatibility firmware and they worked instantly (FS also offered to return and reprogram but we needed it fast).

This was a big shock after dealing with nothing but CAT5/6/RJ45 that has been stable and common for decades (?).