I'm designing a network using the MS450-12 as the core, and trying to find out how to connect the MX-250 for the gateway connection (they want a 40gig core network for high speed east-west).
According to Cisco - the CVR-QSFP-SFP10G is in the transceiver matrix, so that I can convert a QSFP port to an SFP port, and connect the MX-250 that way. I'm just confirming if anyone has tried this successfully.
Yes I believe this will work fine, the 40G ports cannot natively downshift to 10G, and the 4x10 "octopus" breakout cables are not supported I believe, but I believe you're asking about using CVR-QSFP-SFP10G to step-down from 40G to 10G and then perhaps use a 10G TwinAx cable from the MS450 to the MX250 and I'd expect that to work. Let me know if I misunderstood.
I see, according to the Cisco documentation you could use the adapter.
However if you're doing a pure layered design where distribution switches only connect to access layer switches you actually connect the MX'es to an access stack instead of directly on the distribution layer. But that is of course if you want to be nitpicky in the design.