Hi, TL;DR it works.   I have tested it with a Fortigate 100F and a Meraki MS425 now. I connected the Fortigate via x1 to Port 31 on the MS425 via 10G SFP+ modules. I mirrored the traffic to port 3 (1G copper sfp) on the MS425. I connected my laptop to port 3 and 5 (also 1G copper sfp) on the MS425 and started pinging the firewall via port 5. I opened up wireshark and captured the traffic from port3. I was able to see the icmp packets from port 5 to the firewall via port 31.   I did not test it with a stack though. It was just a single MS425.   Hope this helps someone.   @Merakiyou might want to add this information to the documentation. ... View more