This is the necessary cable. https://www.fs.com/de-en/products/30827.html
You can just connect a normal fiber between a 10G SFP and a 40G QSFP and let the 40G end auto negotiate to 10G. Fanout cables are better for density though.
Does 40G QSFP transponder be able to even communicate with 10G SFP? Do they even have the same encoding? OOK? QPSK?
Seems to work mostly fine: https://community.fs.com/blog/40g-qsfp-to-10g-sfp-configuration-guide.html
Considerations for QSFP+ to SFP+ Split
Usually, this split configuration is supported on most switches provided by different vendors regardless of standalone and stacked ones. Certainly, you still need to check this function in the instruction of your switch or consult your vendor, as it’s the most basic condition of splitting QSFP+ to SFP+ configuration. Sometimes, most ports on a switch support split, but some don’t. In other cases, when a switch is deployed as a leaf switch, some ports do not support the split. Or when the port is already used as a stack port, this may also limit split configuration. Thus the conditions can be quite different based on your applications.
Yeah they would need a breakout cable. And there’s no way in hell they can have a link of 40G via SFP+ to a 10G appliance.
Agreed that they can’t get a 40G link when attaching to a 10G device, but the 40G QSFP can be split into 4 10G SFP+ connections instead
