The recommended topologies are shown in this document, https://documentation.meraki.com/MX/Deployment_Guides/MX_Warm_Spare_-_High_Availability_Pair. However these don't cover the scenario with only a single LAN switch. I would suggest that you have two links from the switch to each of the MX, that way the failure of a single link won't cause a dual active scenario. You will need to ensure your LAN switch supports Spanning-Tree Protocol (STP) so that you don't end up with a Layer 2 loop. ... View more