To start, the CMSS is a Cisco "specialist" level certification, whereas the CCNA is an "associate" level certification. Both of these last 3 years when you obtain it for the first time.
Recertification requirements for Cisco certifications across all levels can be found on the following official Cisco page: https://www.cisco.com/c/en/us/training-events/training-certifications/recertification-policy.html#~r...
As clearly outlined, the "associate" level certifications can be recertified a handful of different ways, such as by passing any one associate exam or professional concentration exam. Unfortunately, passing a specialist level exam, such as the ECMS exam that grants the CMSS certification, is NOT one of those ways. We have also posted this information on the "CMSS FAQ" page in the Meraki Community:
https://community.meraki.com/t5/FAQ-and-other-resources/CMSS-FAQ/ba-p/98529
It was not part of the original question but a specialist certification such as the CMSS can itself be recertified through a number of different ways, such as passing a professional concentration exam or passing a technology core exam. It is entirely possible/viable for someone to recertify their CMSS certification and CCNA certification simultaneously by passing an exam that has overlap between the two (e.g. passing an expert-level written exam).
