One of the reasons the idea of terminating at the "core" stuck with me is because eventually (hopefully), i'll be deploying a second MX250 as a warm spare and I wanted to build a foundation/standards for the way we'll be doing WAN links. Yeah it's a very common approach, good to put some forethought into it now. Also yes, totally forgot the MX250 has SFP+ WANs so you'll need to convert the media. At this point, I should have 2 direct routes, both default, from each of the ISP's and another direct route from the LAN interface(granted there is only a single flat VLAN for local) In order to be able to manipulate traffic, I believe I would modify the Primary WAN option within the MX interface to change the metric for which route traffic would be going out of. Do I need to setup any static routes? How do I specify the default route config or is that automatic and handled by the MX? Not sure I entirely follow, but let me just over answer it and hope I cover your questions. The core switch if it's L2 will just use the trunk up to the MX where the MX will hold the gateway for all the VLANs you've created. If the core switch is L3 you'd probably have one transit VLAN between the MX and the Core and you'd put a 0.0.0.0/0 route on the core up to the other end (MX) of the transit VLAN, so that all traffic goes back to the MX. You'd have no routes configured on the MS250 if you're running it in L2 mode, and only one configured if you ran it in L3 mode (route to the MX). The MX then would have it's two WAN links which come through the MS250. The MX will NAT the traffic for any private addresses into the two public addresses from each ISP by default. The MX by default is going to not load balance those links, but make WAN1 it's primary. Within Security Appliance > Traffic Shaping in dashboard you're able to turn on load balancing if you want the MX to utilize both internet links, you can make WAN 2 primary, or you could even define certain local VLANs take different internet links based on source or destination. But no default route configuration on the MX is required, by default it will send any traffic it doesn't know about out the WAN interfaces.
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