Which interface type connects the control and forwarding planes on an MX Series device?

On MX Series and other Juniper devices, the fxp1 interface is a dedicated, internal out-of-band management interface used for communication between the Routing Engine (control plane) and the Packet Forwarding Engine (forwarding plane) and other line cards. This separation ensures management traffic does not contend with data plane traffic.

fxp0 is the default out-of-band management interface, primarily for external management access to the Routing Engine, not for internal control/forwarding plane communication.

me0 is the management Ethernet interface on EX Series switches, not MX Series, and it serves for external management access.

ae interfaces are aggregate Ethernet bundles used for combining multiple physical interfaces for increased bandwidth and redundancy in the data plane.