This cable turns a 40Gbps port into four 10Gbps ports

As part of a core refresh, I had a pair of shiny new Nexus 93108TC-EX switches. I needed to connect them to the old core switches using a QSFP to SFP+ breakout cable because the old switch didn’t have any 40Gb ports. I patched everything in and the transceivers looked fine, but when I turned up one of the 10Gb ports connected to the 40Gb ports it just started flapping. The port on the 40Gb side just says the bandwidth was 40000000 and it wasn’t breaking out the channels. I was not able to find any commands for it that were obvious in the CLI, so I start the Googling for the documentation. it took a bit longer to find than I thought it should, so thought I’d share it here to save you some time.

So, turned out I was doing it wrong. Yeah, I know we already figured that out.
The Nexus 3000/9000: Consolidated Interface Breakout configuration document has the instructions for various platforms, but it’s pretty simple:

(config)# interface breakout module 1 port 53 map ?
10g-4x Breaks out a 40G high BW front panel port into four 10G ports
25g-4x Breaks out a 100G high BW front panel port into four 25G ports
50g-2x Breaks out a 100G high BW front panel port into two 50G ports

9k(config)# interface breakout module 1 port 53 map 10g-4x
2017 Jan 20 15:10:39 9k %ETHPORT-5-IF_DOWN_INTERFACE_REMOVED: Interface Ethernet1/53 is down (Interface removed)
2017 Jan 20 15:10:39 9k %VDC_MGR-5-VDC_STATE_CHANGE: vdc 1 state changed to updating
2017 Jan 20 15:10:39 9k %VDC_MGR-5-VDC_STATE_CHANGE: vdc 1 state changed to active
2017 Jan 20 15:10:39 9k %VDC_MGR-5-VDC_MEMBERSHIP_ADD: vdc_mgr: Interface Ethernet1/53/1 has been added to this vdc
2017 Jan 20 15:10:39 9k %VDC_MGR-5-VDC_MEMBERSHIP_ADD: vdc_mgr: Interface Ethernet1/53/2 has been added to this vdc
2017 Jan 20 15:10:39 9k %VDC_MGR-5-VDC_MEMBERSHIP_ADD: vdc_mgr: Interface Ethernet1/53/3 has been added to this vdc
2017 Jan 20 15:10:39 9k %VDC_MGR-5-VDC_MEMBERSHIP_ADD: vdc_mgr: Interface Ethernet1/53/4 has been added to this vdc
2017 Jan 20 15:10:40 9k %ETHPORT-5-IF_DOWN_ADMIN_DOWN: Interface Ethernet1/53/1 is down (Administratively down)
2017 Jan 20 15:10:40 9k %ETHPORT-5-IF_DOWN_ADMIN_DOWN: Interface Ethernet1/53/2 is down (Administratively down)
2017 Jan 20 15:10:40 9k %ETHPORT-5-IF_DOWN_ADMIN_DOWN: Interface Ethernet1/53/3 is down (Administratively down)
2017 Jan 20 15:10:40 9k %ETHPORT-5-IF_DOWN_ADMIN_DOWN: Interface Ethernet1/53/4 is down (Administratively down)

So there you go. In this case, Ethernet 1/53 disappears and is replaced with Ethernet1/53/1 – 4. I hadn’t expected that parameter to be in the global config and had been expecting to find it in the interface configuration. You may now enjoy the full benefit of your breakout cables.

FIN