In case anyone wants the answer to this... this type of cable is meant to be used with the 100GbE end on the switch, and the 25 GbE ends on hosts. A 100 GbE port is simply 4 25Gb channels combined into one fat port. The hardware on the switch backplane takes care of combining the channels so that the packets are received and transmitted in order, when it's connected to another 100GbE port.  The splitter simply lets you use each 25Gb lane separately.  Now if you do connect the 100GbE end to a host NIC, and then plug the 25GbE side into the switch, the #1 cable (of the 4 25Gb cables) will pass traffic at 25 Gbps, because the NIC doesn't know what to do with the other 3 lanes. So in a pinch, you could at least use it for an emergency.
Hi, We would like to use a breakout cable where: - the 100GbE QSFP28 end goes to a Mellanox ConnectX-5 EX nic on a PER640 - the 4x 25GbE SFP28 ends go to a S5248F-ON switch Could you point me to the relevant documentation, please? Thanks.
Using 100GbE to 4x25GbE breakout cables on S5248F-ON switches