Hi,
That's kind of strange cause I got the opposite answer from the support yesterday.
As they mentioned that is not recommended, but it work.
Here is the support answer:
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A new comment has been made on case 05476938:
Hello,
Thank you for contacting Cisco Meraki.
While it is possible to use a mix of 40G DAC and 10G SFP links, we do not recommend implementing this topology.
Regards,
Vijul Bhalla