To what extent has anyone here used that setup? I've tried an MLAG+STP+LACP core of four switches in EXOS 30.2.
Frankly, I have given up and hooked up our actual new gear's OOB mgmt to our old network. I've added serial consoles and even gave them a channel on our MUXes so they can talk to each other freely without impacting the rest. That way I can test the new topology for sure.
In the simulation using EXOS-VM and GNS3 (the VM), not even ARP seemed to have been working properly anymore in the end. It's frustrating when you can capture the incoming ARP using GNS's packet capture, but there simply is no reply although everything seems ok. I doubt EXOS-VM was at fault. Well I made it crash more or less consistently with null pointer dereferences in getTxPifFromLif [exvlan] and whatnot when playing with lags.
Do you use EXOS-VM (+GNS) for anything more than checking out the CLI and configuring a few VLANs maybe?