I take it your DC MX is also a Hub?   I'd raise a case with Meraki Support - one of the first things they will likely check is whether the back end option to prevent Hubs forming tunnels / exchanging routes with other Hubs is enabled.   This is often done in environments with multiple DCs or active-active Hubs in the same DC, to prevent routing loops. In the first instance, running some pcaps on the MXs at each end should reveal whether the MXs are sending out the appropriate packets to the remote destination - also what packets (if any) are being received at the far end.  You should be able to compare the dynamic ports for match and whether they're being received as expected (i.e. via any upstream NATs  PATs) ... View more