QSFP functionality & compatibility

[nixcraft]

Up to now I've only dealt with SFP & SFP+ ports and I'm not familiar with QSFP yet. So a few questions.

• If connecting a QSFP port to a 10 Gb device with a breakout cable, can a lane be bonded with LACP with another lane and port from a different switch in the stack?
• Are all the lanes usable as separate ports for separate devices, or will for example the LACP bond reserve all the lanes. Are there any limitations or do the lanes behave like any traditional switch port?
• Would an adapter like QSFP-SFPP-ADPT be better for connecting 10 Gb devices and forming LAGs? At least it costs less if the other lanes are not needed.
• Are the Extreme DAC cables compatible with generic server hardware or is it better to use optical modules certified for the specific hardware and skip DAC's unless connecting to other Extreme gear?

I'm looking at the X870 series as a future proofed server rack switch for hardware that is currently 10 Gb but could be upgraded to 25 Gb, 40 Gb or 100 Gb in the future.

[FredrikB-NN2]

What I mean is that if you use only one lane out of four, the three remaining are wasted. With a QSFP suitable for breakout they could be used. I was merely trying to point out (for OP that claims not to be so familiar with QSFPs) that it may be a good idea to investigate breakout options if lots of ports need SFP+/SFP28. Having said that, I have a customer that has a 24 port QSFP+ switch with only QSFP/SFP adapters in it except for uplink, so there are certainly cases where this is the most economical option.

Also, sometimes breakout is not possible, as with CWDM plugs or LR for more than 2 km with supported optics, and then you have to "waste" those three lanes.