I have implemented this on my MX85 and it is working fine, now. I inserted the Copper SFP in Ports #1 and #2, rebooted the firewall and moved the ethernet connections over to the SFP ports. Once I verified those were working again, then I switched over to Multi-WAN and connected my MG51 to Port #4. The MX was able to pull an IPV4 address from the MG51 NAT Pool. I tried disconnected the ethernet cables from both SFP modules and the firewall did not switch over to WAN3. The firewall completely dropped off the internet and the dashboard. I connected both internet ethernet cables back to the MX and once those came back up and the MX was visible on the dashboard, I rebooted the MX again. Once the MX came up, I tried again to unplug both internet ethernet cables and this time the firewall did switch over to WAN3. It also sent an email alert stating that it had switched over to the cellular port. In this case that is correct, but I think the alert should say WAN3 and not the cellular port. I connected the two internet ethernet ports back to the MX and it immediately started using them again. So a second reboot of the firewall after switching to Multi-WAN seems necessary for the failover to WAN3 to work correctly. One bug that I see is that even though IPV6 is enabled on WAN3, the MX is not pulling an IPV6 address from my MG51, which is getting an IPV6 address from the cellular carrier and is enabled to pass IPV6 through to the MX. Overall, the implementation of Multi-WAN is not too bad, but finding out that a second reboot of the firewall is necessary for the failover to work was a nasty surprise that will likely impact many customers that choose this feature. Maybe this is also a bug that will be fixed in future firmware versions?
... View more