Okay ... i really thought that enforcing a certain brand of cables was a thing of the past. Apparently not as reported by @randybias on his Twitter timeline:

This is really a common problem as shown here or here. Especially the later one is showing the pain you could experience when you use those 10GbE direct attach cables . You have to think about this DAC like two hardwired transceivers). As both ends contain the transceiver logic it's easy to implement an ID rom in that cable and check it before bringing up the link.

I should note, that there is a standard for the interface that connects those DACs to the switches/NICs. It's called SFF 8431. But now lets look into reality: The Intel card of the user in the second links doesn't support the DAC cables from HP. HP seems to just support HP cables, not allowing anyone to use other cables by software. Switches from HP are equally rigid, they just support HP branded DACs and nothing else. Cisco Nexus switches seems to have at least a mechanism to allow unsupported DACs to work to get HP cables running . Randy wasn't able to use Arista DACs with HP Flex 10.

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