+1 I believe it's supported/implemented but not documented. That being said, there's at least one instance in the community where a crossover cable was required between and MX WAN port and the ISP device - Solved: MX64 Internet port link drops at 100/full (okay on auto / auto) - The Meraki Community. However, it seems likely that it was the ISP device that didn't support auto MDI.
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