Currently we have a Cisco ISR router that we have a PRI coming into today. We are in the process of migrating to a new carrier for MPLS and plan on retaining the existing PRI until we can move to a cloud based solution for VoiP. As a result, we have to disconnect our old MPLS circuit which comes into the ISR router today, and bring the now MPLS circuit into the MX device, connect the ISR to a LAN port on the MX, then have a meraki switch connected to the ISR. So my question is what is the best way ensure that we have the ISR router to the MX65? Should I configure private ip on a interface in the ISR, and point a static route from the MX to the ISR?