I seem to have lost of first reply, so here goes again.  I'm going to assume your MX84 WAN interface is statically addressed rather than using something like PPPoE.   Your options include: Get a spare switch.  Plug your Internet circuit, MX WAN port and the router into it. Use an existing managed switch.  Created a new VLAN.  Put three ports into it in access mode.  Plug your MX WAN port, Internet circuit and router into it. Ugly.  On your MX create a new VLAN.  Assign it a random subnet that is not in use.  Put three LAN ports of your MX into this VLAN in access mode.  Plug your MX WAN port into one of these MX LAN ports.  Plug the Internet circuit and router into the other two ports. ... View more