I am having the same problem with the CSS326-24G-2S+ on the SFP+ ports. I am connecting a workstation with an Intel X520 10Gb card and Fiberstore Cisco SFP-10G-SR SFP+ modules. My Linux dmesg is full of this: ixgbe 0000:42:00.1 enp66s0f1: NIC Link is Down ixgbe 0000:42:00.1 enp66s0f1: NIC Link is Up...