Best way to hang ISR off of MX65

[SmartWater1010]

Hello, 

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?

 

[PhilipDAth]

I don't see any point in running all traffic through the ISR when the only thing it is processing is PRI voice traffic.  I would plug it into the Meraki switch using a single Ethernet interface.

You could even put the ISR and all the phones into a separate voice VLAN.