If the MX does use automatically WAN2 when WAN1 goes down and you are connected to either a Cisco ASA or FTD. You can simply configure the tunnel on the ASA/FTD twice.   If WAN2 does not answer to the ASA/FTD as long as WAN1 is working only one tunnel is UP at a time.   You can setup a second tunnel is ASA/FTD as long as the destination public ip of the tunnel is diffrent. The SA of the tunnel can be the same. ... View more