If you have two links on an MX at one site and two at another site, the SD-WAN will build over both (at least when they are MPLS links) and you get the combined bandwidth, not for a single stream, but for the traffic as a whole. The links can all be unequal as long as you tell the MX what each one is. You can also control to a degree how much traffic goes over each link depending on latency, packet loss etc. so it is 'smart'
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