10Gtekfor Cisco QSFP-4SFP10G-CU5M, 40Gb/s QSFP+ to 4xSFP+ Direct Attach Breakout Cable, Passive, 5-Meter

Getting this cable was a good news/bad news situation for me. I have a Mikrotik CRS354-48G-4S+2Q+RM and a Mellanox ConnectX3 with a spare QSFP port and I was hoping to split that 40G port from the NIC into 4x10G SFP breakouts, mainly so I can have a dedicated connection other than my 40G fiber connection from the first QSFP port on the nic to a QSFP port on the switch. I was expecting the second port to show up as four separate nics with this cable, but that is not the case. Turns out the ConnectX 3 does not support breakout cables. However, the first cable of the four did work, so I was still able to get one 10G connection from the second NIC QSFP port to an SFP+ port on the switch, it's just that cable 2-4 are dead appendages.I was going to return the breakout cable and just focus on a single cable solution since I could only get one physical network connection out of that second NIC port anyway, but after pricing it out, this looks like it ended up being the cheapest way to get a 10G connection setup between that second port and the switch. This cable was only $35, and the next cheapest option involved a QSA adapter (QSFP->SFP+) for $50 and an SFP+ DAC cable for $10, so $60 total. It's not worth the hassle of returning and paying an additional $25 just to not have those 3 dead cables hanging there.So the cable works and I do have a solid 10G connection with it, but just one which is the fault of the NIC, not the cable.> iperf -c <IP> -w 1M -P 8...[SUM] 0.0000-10.0003 sec 11.0 GBytes 9.41 Gbits/sec

This worked in an older Cisco Datacenter Nexus switch taking the QSFP port and converting it to 4 separate 10GB direct attached ports. Plugged straight into my Dell R710 without issue. Proxmox recognized the connection without any special work around.

I have a couple mikrotik 100gbps switches for backhaul across our farm. Each end has one or two devices that support 100gbps, but this has been a life saver to connect to the switching infrastructure backhaul.Make sure you manually select / setup the link correctly in switchOS, these will show up as multiple connections. At the end of the day though, these were perfect and saved me from having to put even more equipment in already constrained installs.

I needed a DAC to bridge my main network with my new 100gig switch and this fit the bill as it could split a qsfp+ to sfp+. I am only using a fourth of the cable but it is allowing me to get 10gig back to the main network rather than the emergency 100meg management link I was using. I found turning off auto negotiation and manually setting it to 10g along with fsc to off waas the working combo for me.

QSFP port connected to a Microtik CRS504-4XQ-IN, ports configured for 10GBASE-CR, SFP+ connected to a Quanta LB6M with Brocade firmware. Linked up and passing traffic no issues.